The latest Flownex® 2022 release brings you a new transient solver, new mixture capabilities, our machine learning-powered reduced order model (ROM) builder and more!  Read our detailed release notes here.

The new transient solver is a non-iterative solver that can be selected on the fly and provides the capability of solving transient simulations up to 10 times faster. It is also now possible to create mixtures of mixtures specifically that a liquid and gas mixture can now be defined as consisting of a mixture of gases and a mixture of liquids. Through a new machine learning module, users can now create a ROM of their network which can be exported as an FMU. A built-in video recorder can now be used to record graphs and the screen synchronized with transient solving. Other enhancements include updates to the two-phase heat transfer correlations thereby improving the accuracy of two-phase heat transfer simulations. The latest Flownex® is also natively 4K compatible with an enhanced user experience related to graphs, scripts and other features.



New Non-Iterative Transient Solver

A new non-iterative transient solver has been implemented in Flownex®. Compared to the customary iterative solver, the non-iterative transient solver increases solve speed substantially during transient events by eliminating the need to iterate within time steps. This becomes very advantageous for networks of all sizes, but especially where large systems need to be modelled over a prolonged time span.

The user can switch between the iterative transient solver and the non-iterative transient solver via the dropdown provided in the Transient solver settings category on the Flow Solver input dialogue. For easy access, a direct toggle between the solvers was added as a tab to the Home ribbon as well.

Fig. 1 - Non-Iterative Transient Solver Toggle on the Home Ribbon.
Fig. 2 - Non-Iterative Transient Solver Selection Option in the Flow Solver.

The non-iterative transient solver retains the implicit pressure-velocity coupling in use for the iterative solver, thereby maximizing numerical stability in typical flow systems. Since the pressure-flow solution is not iterated with respect to the enthalpy solution, the method may be classified as semi-implicit.

Instead of using successive iteration with underrelaxation to obtain a converged solution, all governing equations are fully linearized with respect to the primary variables as well as the temporal variable, using exact and accurate gradients and derivatives without any relaxation. For this reason, all inputs within the Convergence, Relaxation Parameter as well as the Iterations categories become redundant when using the non-iterative transient solver option.

Mixture Generalization

The capability to create a mixture of fluids has been expanded to create mixtures of mixtures for all fluid types, with the exception of two-phase fluids. When a fluid mixture is created, the user now has the option to select more than one liquid and more than one gas when creating mixtures for each of those phases. The below figure shows a Gas and Liquid Mixture, where the user can create a liquid mixture and a gas mixture that consists of multiple liquids and gases within the liquid-gas mixture.

Fig. 3 - Example of a Gas and Liquid Mixture with a Mixture of Gases and a Mixture of Liquids.

Mixing rules for transport properties are applied to the individual phases separately and in the case of a liquid-gas mixture, additional liquid-gas mixing rules are applied when determining the transport properties of the liquid-gas mixture-of-mixtures.

To use the new capability a mixture is configured in the Fluid mixture specification dialog.  The remaining user interface experience has not changed.  Mixture mass fraction boundary conditions are specified as before, with the list of fluid components expanded to include all of the components of the mixture.

Fig. 4 - Specifying Mass Fractions of a Liquid-Gas Mixture which Contains a Liquid Mixture and Gas Mixture.

Similarly, the result property displays the fluid component mass fraction results for the expanded mixture of mixtures, as seen in Figure 5.

Fig. 5 - Mass Fraction Results of a Liquid-Gas Mixture which Contains a Liquid Mixture and Gas Mixture.

As phase transitions in two-phase fluids are significantly impacted by the presence of other two-phase fluids, the new mixture capability does not currently include the possibility to create a mixture of two-phase fluids.  It is however possible to create a Two-Phase Fluid and Gas Mixture where a mixture of gasses can be specified with a single two-phase fluid, as seen in Figure 6.

Fig. 6 - Two-Phase Fluid and Gas Mixture.

ROM Builder

The Flownex® ROM (Reduced Order Model) Builder generates a multi-platform enabled FMU (Functional Mock-up Unit) containing a Neural Network that was trained on sensitivity analysis data. The user is guided from specifying the input and result properties, creating sample data in a sensitivity analysis, specifying the Neural Network hyperparameters, evaluating the trained Neural Network to exporting the FMU ROM using one convenient dialog. The ROM Builder Configuration dialog can be seen in the image below:

Fig. 7 - ROM Builder Configuration.
Fig. 8 - ROM Builder training a Neural Network

Video Recorder

The capability has been added to record graphs and the screen synchronized with transient solving. The video recording options are added to the properties of each graph. When “Record graph as video” is set to “Yes”, a new video is recorded for each transient run. From the Video Recorder task properties (under Solvers), Flownex® can be configured to record the whole screen.

Fig. 9 - Recording a graph to the Videos folder.

Two Phase Flow Heat Transfer

The two-phase fluid generator has been updated to include Steiner and Taborek normalized coefficients and includes an updated radiation model specification. In previous versions the Steiner and Taborek normalized coefficients were effectively hardcoded and were only available for a limited number of two-phase fluids.  These coefficients have now been moved to the two-phase fluid data files and the fluid generator therefore required updating to allow the user to provide the appropriate values for generated fluids.  The latest two-phase data file format also provides for the selection of the radiation participation model to be used for the generated fluid.

Fig. 10 - Two-Phase Fluid Importer with Saturated Boiling and Radiation Model Specification.


User Interface Framework

Higher resolution (4K) compatibility has been added to the Graphical User Interface.


The capability to specify a Ramp action has been added. When a Ramp action is created, the user can specify the duration and final value for the action rather than the coefficients for a straight line.

Fig. 11 - Ramp Action.


  • The mils unit has been added that is used for vibration.
  • Added the capability for a user to reset the unit of a property to the current selected unit system default. This option is available on the context menu on a property, as seen below.
Fig. 12 - Reset Unit Option.


  • Added a property to change point symbols to be solid or hollow.
  • Added a ThinCross symbol type.
Fig. 13 - ThinCross Symbol Type and Solid Symbol Option Properties added to Graphs.
  • Grouping line items with the same unit group onto one Y-axis is now possible. The “Display multiple Y-Axis” property has been replaced with ”Axes displayed” property.
Fig. 14 - Axes Displayed Property.
Fig. 15 -Axes Displayed Property.

Component Characteristic Graphs

  • An option to view all Angles on Compressor Component Characteristic Graph has been added.
  • Angles are now available to be checked/unchecked from the graph legend.
  • All four dimension’s values of the chart are displayed in the chart tooltip.
  • Only plotting the closest lines functionality is still available by setting a new property: “Show closest background lines” to “Yes”. Property is below “Background lines”.
  • By default, all lines with check boxes will be displayed for new graphs and graphs from older projects.


  • The Script component has been updated such that the “Initialise” function is called only once before Steady State and “Cleanup” is called once after Steady State. This is done if any or all of the options are active for Before, During and After Steady State. Previously it was called multiple times during Steady State if more than one of the options were active.
  • The Iterative Script’s “Initialise” and “Cleanup” functions now works similar to a normal Script and is called before and after every steady state and called before and after every transient.
  • The font of the code editor was changed to a monotype font in order for spacing to align better.
  • A repository was added that allows for easy sharing of values between scripts. The repository of values can also be loaded and saved as needed.
    • The repository is used in the following manner:
      • To add or change a value:

IPS.Scripting.SharedValueRepository.AddOrUpdateDoubleValue(“MyVal”, 10.0);

      • To access a value from a different script:

double val = IPS.Scripting.SharedValueRepository.GetDoubleValue(“MyVal”);

    • The repository supports the following functions:
      • void AddOrUpdateDoubleValue(string Name, double Value);
      • void AddOrUpdateIntegerValue(string Name, int Value);
      • void AddOrUpdateBooleanValue(string Name, bool Value);
      • void AddOrUpdateStringValue(string Name, string Value);
      • void AddOrUpdateValue(string Name, System::Object^ Value);
      • double GetDoubleValue(string Name);
      • int GetIntegerValue(string Name);
      • bool GetBooleanValue(string Name);
      • string GetStringValue(string Name);
      • System::Object^ GetValue(string Name);
      • bool HasValue(string Name);
      • void SaveRepository(string FileName);
      • void LoadRepository(string FileName);


  • An application setting has been added so that new pages have the viewport in the middle of the page. This setting is false by default.
Fig. 16 - Viewpoint in Center for New Pages Setting.


  • Added an application wide setting: “Turn snap before run on by default”. This option is false by default, but a user can make it true, then it will be on for all new projects.
Fig. 17 - Turn Snap Before Run on by Default Option.

PCF Importing

  • Added a default import mapping that imports components other than only pipes as applicable.
Fig. 18 - Import Configuration Dialog.

Data Transfer Links

  • Implemented bi-directional data transfer capability for Data Transfer Links. The user can drag and drop from the left or the right side of the Data Transfer Link Setup dialog. The direction of the transfer is indicated by the arrows. Bi-directional transfers show arrows at both sides, as seen below.
Fig. 19 - Bi-Directional Data Transfer Capability for Data Transfer Links.
  • The letters F and C are displayed on a Data Transfer Link when a factor (F) or constant (C) is used.
Fig. 20 - F and C Displayed on Drawing Page.

Flow Path Graphs

  • Added the ability to plot Flow Path Graphs along the Rotating Annular Gap length and length increments of the Rotating Channel.

Two Phase Pressure Loss

  • Added output for Lockhart-Martinelli two-phase pressure loss calculations and the parameters that are used in its calculation as results.

Heat Transfer

  • Reynolds and Prandtl Number results have been added to convective subdivision element results.
  • Errors have been implemented to prevent Composite Heat Transfer element to Composite Heat Transfer element connection via a solid Node with non-adiabatic boundary conditions, since these are non-physical configurations.

Relap Coupling

  • Added an option to Relap simulation to save every transient step’s output file.
  • Fixed the problem where the minor edits were deleted in Relap files.
  • Allow users to add additional inputs or outputs to the Flow solver coupling. This is especially useful to extract additional results from the Relap simulation.

Command Logging

  • Flownex® logs many of the user actions now to a file. This log is useful to keep track of what was changed in a project and when.
  • The command log files are located in the project folder in the sub folder CmdRec\Logs.
  • Each new Flownex® session starts a new log with the date and time of the session. The user, operating system and computer name are recorded at the top of each file.
  • The following user actions are recorded to the file:
    • Interaction with the drawing canvas (e.g. adding, deleting, selecting components).
    • Interaction with pages (opening, closing, selecting pages).
    • Interaction with snaps (saving, loading).
    • Setting component inputs.
    • Solving commands (solve steady state, transient, stopping etc.).
Fig. 21 - Command Logging Text File.


  • Exported Flownex® FMUs now launch a separate console that communicates with the Flownex® instance that is launched. This is done to enable the FMU binary to be unloaded by the master simulator. The binary was previously locked until the master simulator process shuts down due to the CLR being loaded as part of the binary. All CLR code is now loaded in the separate console process.
  • The locked binary gave a warning or error when the FMU was unloaded, even though the FMU functioned correctly.

NIST Importer

  • The NIST fluid importer was updated to list all the available fluids and mixtures in NIST.


Result Layers

  • Fixed the bug where Result Layers did not update during transient in 3D view.
  • Result Layers are now updated after a Snap is loaded.
  • Fixed absolute value usage in Result Layers.
  • Changed mass flow, volume flow and velocity built in Result Layers to use absolute values.

Velocity PID

  • Fixed the bug where state of the PID was not saved to Snaps.

Drawing Texts

  • Fixed the problem when pressing the Cancel button when changing settings for the drawing texts, the operation was not fully cancelled.

Excel Component

  • Fixed bug where Snaps were not correctly loaded for Excel component if an editor wasn’t opened previously or network wasn’t solved previously.

Results Overview

  • Fixed the bug where the Solving On/Off state was not saved with the project. This meant that the user had to turn it off again every time the user opened a project.


  • Fixed a bug where an exception in the user interface was sometimes shown when using the API. This happened when using the API with a network with open graphs.


  • Added tooltip results for all Junction component types.

Positive Displacement Pump

  • Fixed the unit for NPSH in the characteristic chart.

Excess Flow Valve

  • Added tooltip results for the Excess Flow Valve.


  • Fixed the error where a user could connect multiple views of a node or element to a fiber that should only allow a single connection. This caused an error in the solver that was not very descriptive and hard to trace.

Warnings and Errors

  • Updated MATRIX_NOT_POSITIVE_DEFINITE error to also show the Node related to the error.
  • Added a warning when a large non-normalized energy residual is detected at a node and the energy equations may not have converged.

Neutronics Script

  • Implemented Total power result and Transient Fix power option correctly for the Neutronics Script.
  • Initialisation was not correctly called for the Neutronics Script and a Cleanup function has been added.

Boundary Conditions

  • If Mass source fraction is disabled after being specified, the mass fraction did not reset to 1 and 0, as with the normal mass fraction specification.
  • Fixed the problem where a Data Transfer Link could write and change the temperature of a Boundary Condition even if the option to specify temperature is not turned on.

Heat Transfer

  • Addressed Conduction results that went out of sync when changing from upstream Convection results to Conduction element results after an increment other than 1 is selected for the upstream Convection results.

Two Phase Flow Heat Transfer

  • The Steiner and Taborek reference coefficients are now specified in the two-phase fluid specification file and are no longer hard coded. Approximations have been provided for Flownex® fluids that are not featured in the original Steiner and Taborek paper, and a warning is issued.
  • The heat flux at the critical heat flux conditions is used when the wall temperature commensurate with the critical heat flux that is calculated. Previously the current heat flux result was used in the wall temperature calculation.
  • Updated the Groeneveld critical heat flux and film boiling lookup tables to the latest versions.


  • The Validation Runner was renamed to Verification Runner. The Verification Runner is now included in the Nuclear module and uses the normal Nuclear license and does not require a separate license anymore.


  • Fixed the problem where actions wrongly set integer values at the start of an action. The initial value of the integer property was always added as an offset. This was reported as a multiplexer problem but is a general problem.

FLOWNEX SE 8.12.8 (2021 – UPDATE 1)

FLOWNEX SE 8.12.8 (2021 – UPDATE 1)
The latest Flownex® 2021 update brings you new components, more flexibility and increased user-friendliness as well as bug fixes.
Enhancements include a new Velocity PID component added to the Distributed Control System (DCS) library and improved steady-state solving. Components can now be managed with ease thanks to new features allowing search, multi-select description editing and link display. The Reactor Builder Script and associated Runtime Neutronic Script functionality have also been expanded to include TRISO particle modelling and the effect of Xenon poisoning during reactor transients.



Distributed Control System (DCS)

  • Added a Velocity based PID controller. The goal of the Velocity PID controller is to have a PID that calculates the change of output variables instead of the output itself. This way different controllers can easily be used to control the same variable and switching between them does not cause spikes in the output.
Fig. 10 - Two-Phase Fluid Importer with Saturated Boiling and Radiation Model Specification.
  • Added steady state operation for DCS components. The DCS components can propagate their inputs before or after steady state. The Execute before steady state option ensures that the control system values are initialised and passed to the flow components before the steady state solution is calculated. This results in a smooth change in controlled values when the transient solution starts. The DCS components can also be executed during steady state. In this case, the DCS components will execute as if a transient is being executed using the time step specified in the Scheduler (or Time Step settings). The Steady State behaviour settings for the DCS can be found on the DCS Solver, as seen in Figure 2. By default, the Execute before steady state option will be enabled for new projects and it will be disabled for older projects.
Fig. 2 - DCS Solver Steady State Behaviour Settings.


Component Inputs

  • The handling of structural only rigids with the CAESAR II importer has been improved. They are now ignored and not imported at all.
Fig. 3 - Multi-Editing Component Descriptions and Using the Description to Search for Components using the Find Dialog.
  • A Search feature on the Component Selection dialog has been enabled. Input fields where users select a certain component as input, now shows a dialog with more filters to enable easier location of components in a large network. This works similar to the Find dialog.
Fig. 4 - New Search Feature for the Component Selection Dialog.Figure 4: New Search Feature for the Component Selection Dialog.


  • The component connectivity can be shown by right clicking on any component and choosing “Display Links/Connections” from the context menu. This dialog has been updated to make it easier to understand and now also shows the port and hub names in the connections. The displayed port, fiber and hub names are useful when a user wants to determine which names to use when making connections to specific ports, fibers or hubs using the API.
Fig. 11 - Ramp Action.


  • The ability to specify port names when linking components using the network builder has been added. This is useful for linking components that contain many ports like the DCS controller components.
  • The ability to specify a hub name when connecting components using the API was added. This is useful for linking components that contain several hubs. Details of the new function can be found in the API Help manual.
  • Communication through the API with existing open Flownex instances has been improved. The same functions can now be used to control instances that have been launched by the API or other existing instances. This makes the code simpler, for instance the same Python functions can now be used with both.

Flow Solver

  • Added humid air fluid functions (psychrometric fluid functions) to Material Scripts that enables the calculation of mixture mass fractions from the following three input combinations:
    • Pressure, dry bulb temperature and relative humidity.
    • Pressure, dry bulb temperature and wet bulb temperature.
    • Humidity ratio.
  • Added an error for non-physical user-specified constant convection coefficients. The solver will not run when a negative heat transfer coefficient is specified.
  • Added an option to select between Effective area and Conduction shape factor specification for the Composite Conductivity element.
Fig. 6 - Effective area and Conduction shape factor options.


Compiler warnings were not shown when compiling Scripts. For Script components, the warnings are now shown when using the Debug button. This provides users the opportunity to address any warnings that the Scripts may issue during compilation.

Installation Verification Tool

The installation verification tool has been updated to allow it to run several Flownex instances in parallel. This aids in both increased stability and speed. The user can select the number of parallel instances to use on the user interface. By default, it is set to half the number of available logical processors.

Nuclear Scripts

Reactor Builder Script Changes

  • Cavity flow paths have been updated to:
    • Allow for adjacent vertical cavities to generate separate vertical flow paths.
    • Allow for adjacent horizontal cavities to generate separate horizontal flow paths.
    • Allow the user to specify that adjacent single cavities must remain distinct. This feature can be used in conjunction with the above options, to allow separate connections to flow elements outside of the generated reactor network.
  • Implemented the associations between Ports and Node connection as a list to facilitate removing the previously hardcoded limit of 20 ports.
  • Changed the folder structure and location of feedback files from the project folder to a sub-folder \point_kinetics_inputs\<Reactor drawing page>. The point kinetic input files for a network shown in a page specified in the Reactor drawing page, are now located in the same sub-folder.
    • When the network is generated the first time the default point kinetics input files are copied to this subfolder. A new file, nominal_conditions.txt will be added to the existing list of input files. It will have the nominal power (in kW) as input with the rest of the file consisting of comments lines for the user to specify the nominal conditions associated with the set of point kinetic inputs contained in this sub-folder.
  • Removed the discretization options for the sphere; the option is now always equally spaced. This was done since internal grid independence studies showed superior grid independence for the equally spaced option.
  • A Tri-structural Isotropic (TRISO) model option was added, consisting of one node per fuel kernel, one node per composite coating, and a node on the interface between the fuel and composite coating (for a total of three nodes per TRISO particle). The discretization for this feature is described in the Reactor Builder Script and Runtime Neutronics Script User Manual in Appendix B, Section 5.2.
  • Feedback groups:
    • Removed spurious warning messages when generating a network with general fuel zone specified, that nodes have already been added to a feedback group.
    • Allow for numbered (arbitrary) feedback groups in addition to the named feedback groups.
    • Allow for an unlimited number of materials to be specified per feedback group.

Reactor Result Script Changes

  • Added a feature to specify a period for results file generation during a transient simulation.
  • Added tabular output for newly added TRISO particle results.
  • Added Pebble Wall Node results to Secondary Node result tables.
  • Addressed error in the flow element indexing that resulted in partial table printouts.

Runtime Neutronics Script Changes

  • Runtime Neutronics Script was updated to accommodate the generic/numbered reactivity feedback groups. When the numbered feedback group option is selected then:
    • The number of groups that are active needs to be specified by the user,
    • The feedback group that is associated with the moderator needs to be selected by the user.
  • Updated and properly documented comment lines in all sample point kinetics input files:
    • Added nominal_condition.txt file.
    • Updated comment in heat_distribution.txt to clearly indicate that the first two lines refer to the boundary of the zones and not the zone increments.
  • Added Xenon modelling capability—the model is described in the Reactor Builder Script and Runtime Neutronics Script User Manual in Section 3.2.
    • Xenon parameters are provided in a xenon_transient.txt input file.
    • The reactivity associated with the Xenon along with the normalized Xenon and Iodine concentrations is provided as transient outputs.
  • Nominal power is now read from the nominal_condition.txt input file and shown on the property page for ease of reference after the script has executed once.
  • The “update reference temperature” option has been changed to “Calculation mode” with two options:
    • Initialize/Nominal conditions: This option will update the reference temperature for the feedback groups and set the control rod reactivity to zero.
    • Off-nominal conditions: When this option is selected, the steady state power will become available as input and will be used in the steady state run. The reference temperatures will remain unchanged, and the control rod depth will be adjusted to offset the fuel/moderator/reflector reactivity that resulted from the non-nominal operation.
  • Moved displayed modelling parameters that are read from the point kinetics input files to a separate category (“Read from files in point_kinetic_input folder”) to clearly differentiate them from inputs that should be provided on the property page.

Select Flow Circuit

Added the ability to select all components on the drawing canvas that are part of a specific Flow Circuit (components that are connected and have the same assigned fluid).
This feature can be used by right-clicking on any component in the Flow Circuit and selecting “Select Flow Circuit”. All components in that Flow Circuit will then be selected and their common properties are displayed on the property grid.

Fig. 7 - Select Flow Circuit.


Compound Components

  • Fixed the problem where lists could not be exposed in compounds.
  • Fixed the problem where the result layers were not displayed for some compound components. These included components such as the Gradual Pipe Transition, Orifice in Pipe Transition, Abrupt Contraction and Expansion and Long Orifice. 
  • Fixed the problem where any fiber could connect to an exposed hub from a compound component. This caused a problem where invalid component connections could be made to the Angle Valve, Gate Valve, Globe Valve, Sharp Edge Diaphragm Valve, Sluice Valve, Smooth Diaphragm Valve and Y-Valve.
  • Fixed the problem where a large number of items in the Reactor Chart got duplicated when a user pressed Cancel and the chart was reloaded. This caused the chart file to increase in size every time a user pressed Cancel and kept many unused items in the lists.

Flow Solver Components

  • Removed the incorrect reporting of negative values being calculated for specific heat. This happened when the specific heat polynomial option was used for defining the enthalpy of the fluid, the latter which may be negative.
  • Added a warning when the static pressure of a two-phase fluid at inlet to an ANSI standard based Valve exceeds the critical pressure of the fluid. Under these conditions Flownex® applies the gas-phase equations, not the liquid phase equations.
  • Fixed the reporting of incremental areas on the Rotor disk of the Rotor-Stator component that erroneously reported the outer radius instead of the area.
  • Limited the participating gas partial pressure emissivity correction in the Leckner correlation for gas to surface radiation to zero in order to prevent calculating undefined numerical values.
  • A relaxation parameter was applied to the friction factor for very small non-condensable mass fractions that resulted in non-physical friction factors being calculated. The problem was addressed by removing the relaxation calculation.
  • The incorrect vapor mass fraction approximation was used for determining the specific heat for a two-phase fluid with non-condensable gas during the critical mass flow and static pressure calculation.
  • Addressed issue with Composite Heat Transfer (CHT) convection script indexing for CHT connected to flow nodes by adding an index indicating which index in the parallel path a convection element is associated with. This allows for correct indexing of the associated flow nodes in CHT element convection scripts.
  • When a CHT element is connected to a Node on one side and a sub-divided Pipe on the other, two convective elements were created per increment on the side connected to the Node. This resulted in the subdivided results being displayed incorrectly.
  • Fixed the problem where the Adiabatic Flame element added combustion product species that were not available in the gas mixture list to first fluid in list and not into background fluid.
  • Addressed the incorrect reporting of the pressure difference excluding elevation change result for the Primary side of the Shell and Tube Heat Exchanger. This pressure difference was incorrectly divided by the number of gas passes.
  • Removed the limitation that the CHT element can only be connected between two subdivided elements. CHT elements may now also be connected between a sub-divided element and a single node. The convection heat transfer to a flow Node and the conduction heat transfer to a solid Node is now correctly accounted for. Previously a warning was issued that this topology was not permitted, but the simulation was not stopped and non-physical results were reported.
  • Addressed the incorrect treatment of loss coefficients for sub-divided reactor zones. The user specified loss coefficients were assigned to each element associated with a sub-divided zone, whereas the inlet and outlet loss coefficients are now only applied to the first and last element in a sub-divided string of elements.
  • Fixed problem where two-phase tank level was temporarily set to zero when loading a snap.
  • Fixed precursor equation in solid and liquid fuel nuclear example scripts.

Excel Input Sheets

  • Fixed the problem where data was lost when a user performed a save-as operation on a project after editing Excel input sheets.


  • Fixed the problem where some example Script components were available for use in the Basic Thermal Fluid module.

GIS Importing

  • When importing GIS files, the generation of background maps using some online sources did not function correctly anymore. The importing was updated to remove sources that do not work anymore and the speed of importing was significantly improved.

Initialize Steady State from Snap Files

  • The problem was fixed where the fixed mass flow value was used from the snap file and not from the user interface specification when initializing a steady state from a snap file.The problem was fixed where the fixed mass flow value was used from the snap file and not from the user interface specification when initializing a steady state from a snap file.

FLOWNEX SE 8.12.7 (2021)

FLOWNEX SE 8.12.7 (2021)

The latest release of Flownex® for 2021 comes with much anticipated enhancements and fixes to ensure that you can do even more with real world systems simulation.

Some of these include the option to initialise the steady state solver from a previously saved snap, specifying transient actions through tables, python link functionality. With the support of Adobe Flash having come to an end we have updated our video tutorials to now work with HTML5.



Start Steady State from Previous Conditions

A steady state solve can now be initialised from conditions from any saved snap. The user can use this to initialise a steady state solution from a previous steady state solution or from a transient run.

The setting can be activated on the Flow Solver Properties Inputs window, where the related snap can be selected, as seen in Figure 1.

Fig. 1 - Initialise Steady State from Snap Option in Flow Solver Inputs

Action Specifications via Tables

A table can now be used to specify the value of an input at a specified time in an action. The table allows the user to copy and paste data from Excel. Values will be extrapolated if the time values fall outside the range specified in the table.

Fig. 2 - Table Input Option in Actions

Video Tutorials

The video tutorials in the Flownex® startup page that used Adobe Flash has been replaced by HTML5 videos. This was necessitated by Adobe not supporting Flash since 1 January 2021.
Fig. 3 - Flownex Video Tutorials


Caesar II Link

  • The handling of structural only rigids with the CAESAR II importer has been improved. They are now ignored and not imported at all.

Global Parameters

  • The way global parameters are handled with snaps has been improved. The values will be read in from a snap. The number of parameters and the number of associated properties (as well as which properties are associated) will not be changed when reading in a snap.

Python Link

  • The Python API files now contains a function that allows the user to run the Flownex® Designer using Python.

Finned Tube Heat Exchanger

  • Added an improved default Finned Tube Heat Transfer calculation example script for the Finned Tube Heat Exchanger – Fin Side.
  • The description of the input “Tube pass length” has been changed to clarify that this input represents the total primary flow path length.

License Borrowing

  • The maximum number of days a license can be borrowed, as specified in the server license file, is now indicated on the Borrow License dialog, rather than the default 28 days.
Fig. 4 - Number of Days to Borrow License from Server

Energy Solver Convergence Enhancement

  • The warnings associated with node temperature changes were enhanced to facilitate the identification of the non-converged node.
  • An option was added to the Flow Solver settings to exclude nodes with temperature changes as a result of very small mass flows in its associated flow element.
Fig. 5 - Apply Mass Flow Rate Threshold to Transient Temperature Change Residual


Excel Reporting

  • Fixed the problem where the option to “open in Excel” sometimes opened multiple copies of the Excel template.

Parameter Display

  • Fixed the problem where the parameter display did not work correctly during transient, which sometimes caused the application to terminate.

Heat Transfer Correlations

  • Fixed the problem where a warning was shown when the Gnielinski correlation was used that stated that the roughness used in the correlation is different from the Pipe roughness, even when the user specified the option that the roughness from the Pipe should be used.

Isentropic Head Compressor

  • Updated the maximum number of constant speed curves (61 to 101), data elements in a row (61 to 101) and constant blade angle maps (31 to 51) for the Isentropic Head Compressor Chart.

Variable Speed Pump

  • Fixed the pump shut down speed option that did not execute correctly.
  • Fixed the unit problem with pump shut down speed.

Slurry Flow

  • Fixed the vertical slurry frictional pressure drop calculation, which used the mixture density instead of fines density.


  • Changed the two-phase Bend gross secondary loss factor to display results without multiplication factors.

Flow Path Graph

  • Fixed the bug where the unit of a plotted line item is not removed when the Property is changed to a unitless property.

FLOWNEX SE 8.12.6 (2020 – UPDATE 2)

FLOWNEX SE 8.12.6 (2020 – UPDATE 2)

The second update of Flownex® SE for 2020 further expands the possibilities of simulating real-world systems.

Exciting features for this update are a reworked deep solver coupling with Ansys Mechanical for explicit transient co-simulation and automated Nuclear Reactor building script along with many minor enhancements described below.



Ansys Mechanical Coupling

The Ansys Mechanical Flow Solver Coupling component has been improved to allow the simulation of complex 3D conduction and stress in Ansys Mechanical coupled to a flow and heat transfer simulation in Flownex®. This enhancement includes the addition of a deep solver coupling between Flownex® and Ansys Mechanical, allowing data exchange between iterations, full transient co-simulation functionality and unit integration.
Figure 1: Ansys Mechanical Coupling

Nuclear Reactor Builder Scripts

Script Generated Reactor Results

Results in tabular form corresponding to the grid layout of the generated reactor network are written to a text file in the ScriptResults subfolder of the project folder. The tabular results are reported at the end of a steady state run as well as during user specified times and at the end of transient runs. A feature is provided to specify output variables that are reported at every time step. These results are written to a comma separated values (csv) file as a time series residing in the ScriptResults subfolder.

Reactor Generation Script

Various improvements were made to the geometric parameter calculations. Network topology generation for the transitions between different types of reactor zones was extended.

Figure 2: Reactor Generation Script Enhancements



The “Description”, “Minimum” and “Maximum” values have been added to the imported FMU variables. The description will be displayed if it is not blank. Minimum and maximum values will be displayed if they are specified in the FMU and the “Display variable information” property is turned on. A warning is given if the minimum or maximum values for inputs are exceeded.

Figure 3: Description, Minimum and Maximum Values added to Imported FMU’s


The License modules selection have been updated so that it can work for users that do not have write access to their ProgramData folders.


  • Functions to retrieve minimum and maximum temperatures and pressures, as well as critical temperatures and pressures from two-phase fluids via Scripts have been added.
  • Added the ability for Scripts to properly work with lists and Snaps – functions were added that get called in the Script before and after loading and saving Snaps. This gives users flexibility to implement their own Snap saving and loading code.

Composite Heat Transfer Component

The “Area multiplication factor” input for the Composite Heat Transfer (CHT) component has been moved to a separate category to indicate that the input is applied to all surfaces.

Figure 4: Area Multiplication Factor Moved to Separate Category



Fixed the problem where many of the modules were missing when using a borrowed license from the server.

Find Dialog

Fixed the problem where the Find dialog did not open the property page for components on closed pages (it appeared that multi edit did not work).


Line Graph: Removed trailing list separator from the ‘Save As CSV’ file rows.


  • Fixed the Solid Properties script, as the script did not compile correctly due to the enthalpy function that was removed.
  • Fixed the problem where properties for two-phase non condensable mixtures returned zero values as results in the Mixed Fluid Properties Script.

Solver Results

Fixed the problem where the Fluid volume and Fluid mass results in the Flow Solver Results window did not update when it was linked to an Action or displayed on the canvas.

Composite Heat Transfer Component

  • Fixed the problem where an error was issued when connecting the Composite Heat Transfer element to non-pipe flow elements because the roughness could not be determined when the Dittus-Boelter option was specified.
  • Fixed the Composite Heat Transfer element StPr chart option not allowing the user to specify the flow area.
  • Fixed the Reynolds number result on the Composite Heat Transfer element for StPr chart input option not displaying correctly.

FLOWNEX SE 8.12.5 (2020 – UPDATE 1)

FLOWNEX SE 8.12.5 (2020 – UPDATE 1)
The new Update to Flownex® SE for 2020 expands the possibilities of simulating real-world systems. Some exciting features included with this release include: built-in functionality to generate system resistance curves within seconds, force calculations for pipe sections, interfacing with CAESAR II for detailed pipe stress analyses, a co-simulation link to the latest version of 6SigmaDCX, along with many other improvements that are listed below.



System Resistance Graphs

The capability has been added to easily plot system resistance graphs. At the click of a button, a parametric run is automatically configured and executed providing the user with an accurate system resistance graph in seconds, as seen in Figure 4. The system resistance graph can be exported as a CSV file in a few clicks and sent to a manufacturer for pump selection. The system resistance graph can also be plotted on a pump chart allowing the user to quickly determine operating points at different pumps speeds.
Figure 3: System Resistance Graph added to Operating Point Plots.
Figure 4- System Resistance Curve and Pump Curve Plot

Force Calculations for Piping Sections

It is not possible to perform structural pipe analysis for water hammer scenarios in most real world systems using hand calculations due to the complex nature of the pressure wave reflections. Flownex® already provides the capabilities to simulate fast transients such as water hammer in these complex systems. In this release, enhancements have been made to the axial pipe force calculations to make them valid for all steady state and transient simulations. This allows users to easily simulate the pipe forces in Flownex® and export the results to structural codes such as ROHR 2 and CAESAR II. Pipe sections for net force calculations can also easily be defined in the “Force Calculation Piping Sections” dialog that is available under the Results menu.
Figure 5. Calculated Pipe Forces in Flownex
The enhanced force calculations are applicable to Pipes, Bends, Valves, the British Standard Orifice, Secondary Loss and the General Empirical Relationship components.

CAESAR II Integration

Flownex® provides a very easy to use interface to work with CAESAR II. By using this interface Flownex® can calculate dynamic loads for pipe stress simulations for water hammer cases or pressure waves. The interface allows a user to import the geometry for a piping system from CAESAR II directly into Flownex®. This saves a user time and also eliminates possible errors that could occur when users need to manually duplicate piping systems in Flownex®. Flownex® also provides an intuitive way to define the piping sections for which users wants the net forces to be calculated. These calculated forces can be automatically exported in a time series that is easily imported into CAESAR II.
Figure 5- Imported Pipeline and Calculated Pipe Forces in Flownex.
Figure 6- Forces Imported to CAESAR II.

6Sigma Link

6Sigma is a world leading tool for data centre simulation and a link to 6Sigma has been added. The link allows users to quickly setup combined simulations and allows both steady state and full transient simulations. Typically, a detailed model of the inside of a data centre can be connected to a complete external cooling model in Flownex®, where all the cooling towers, pumps, heat exchangers etc. is modelled in detail. This allows a complete system simulation that is not available in other software and opens up a whole new spectrum of possible efficiency improvements in both design and operation mythology.
Figure 7- 6Sigma Link Example.

Nuclear Reactor Building Scripts

The ability has been added to build a nuclear reactor using a script. This script reads information from a reactor geometry chart and builds a corresponding reactor. The reactor is built on a separate page in the user interface. Users have access to all of the elements and nodes that defines the reactor.

There are several advantages using this capability. The first advantage is that all the inputs to the elements and nodes that build the reactor can be verified. Furthermore, all internal results are available and finally, the internal connectivity and structure can be manually modified by users if needed.

 Example scripts are available on request. Some components have been added to aid in the reactor building, which include a Porous Flow Element and a Composite Conduction component. They are found in the Reactor Building Blocks category in the Nuclear library, as seen in Figure 9.

Figure 8- Generated Reactor using the Nuclear Reactor Building Scripts.
Figure 9- Composite Conductivity and Porous Flow Element added to Nuclear Library.

Relap Component

The Relap component has been updated to work with newer versions of Relap. Newly updated examples are available on request.

Angled T-Junctions and Y-Junctions

The existing junction functionality has been enhanced to include the ability to model angled T-junctions and Y-junctions, as seen in Figure 1.

Many of the junction losses as defined in “Internal Flow Systems, 2nd Edition” by D. S. Miller have been implemented, thereby extending the previous functionality from the limited perpendicular junction options. These junctions are available for selection from pre-defined junction types, as seen in Figure 2.

Figure 1: T-Junction and Y-Junction Components in Flownex®.
Figure 2: Junction Branch Angle Options for Converging T-Junctions.

Mathcad Component

A new Mathcad link has been added to work with Mathcad Prime version 4.0, 5.0 and 6.0.
Figure 10- Mathcad Prime Link

Graph Improvements

Graphs that have been disabled, now shows a red cross on them to easily identify disabled graphs, as seen in Figure 11. The “Save As CSV” option has been added to all graph types and is available on the context menu of a graph, as seen in Figure 12.
Figure 11-Disabled Graph in Flownex®.
Figure 12- “Save As CSV” Option added to Graphs.

Licensing System

The licensing system has been updated to Version 14. Subsequently all users using server licenses will need to install Version 14 of the license server. An installer that does the upgrade is available to download from our website or from Support. There are several fixes in the newer version of the license server. More information about the fixes is available on the RLM website.

Trace Elements

The trace element modelling capability has been significantly expanded. Previous versions only allowed for homogeneous mixing of trace elements on nodes, where users now have the following additional capabilities at their disposal:

  • The ability to filter trace elements from the network.
  • The ability to specify selective throughflow of trace elements between nodes, thus resulting in non-homogenous mixing of trace elements within nodes.
  • The ability to specify trace element sources and sinks on nodes without the precondition that they enter or leave the system via mass sources or sinks defined for the carrier fluid.
  • Modelling trace element decay during transients using the trace element decay constant.

Filtering and selective throughflow of trace elements are specified on flow element components and sources or sinks and decay are specified on node components, as seen in Figure 13.

Figure 13- New Trace Element Input Options on Nodes.

Isentropic Head Compressor

A new compressor type has been added specifically for modelling compressors operating near the critical point of the fluid with significant changes in fluid properties such as the specific heat, making the use of conventional gas flow dimensionless parameters less accurate. The Isentropic Head Compressor uses isentropic head vs. volume flow data at different speeds. Given the volume flow and speed, the isentropic head is interpolated from the characteristic curve, after which real gas entropy tables are used to find the corresponding pressure.
Figure 14- Isentropic Head Compressor in the Turbos and Pumps Library.


Video Tutorials

The video tutorials can now be played with a built-in player in Flownex® eliminating problems of browser compatibility. Adobe Flash player needs to be installed for the player to work.

Result Layers

For gradient result layers, components were not coloured when they had properties smaller than the minimum value or larger than the maximum value. A new option has been added namely: “Gradient <-[MinValue, MaxValue]->”, as seen in Figure 15. With this option the components with properties lower than the minimum value is painted the minimum colour and components with properties higher than the maximum is painted the maximum colour. This option is now set as the default option.
Figure 15- Gradient Option in Result Layers.

Property Grid

Disabled input properties did not allow users to change their units. This has been changed since these fields display valuable information which users may want to view in different units, as seen in Figure 16.
Figure 16- Units Can be Changed for Disabled Properties.
Figure 17- Toggle Button for Properties.

Screenshot Preview

The screenshot preview that displays in Windows Explorer when the preview pane view is activated, has been updated. In the past, the entire Flownex® window area was captured and sometimes it included overlapping windows. Now only the main item inside Flownex® is captured in order to show the most relevant view of the project, as seen in Figure 18. 

Figure 18- Screenshot Preview.

Psychrometric Boundary Condition

The “Not specified” option as a Boundary condition type, has been added to the Psychrometric Boundary Condition. This option has been added so that the specified condition can be unfixed during a transient simulation.
Figure 19- Not Specified Option for the Psychrometric Boundary Condition.

Heat Transfer

The following enhancements has been made to the heat transfer components:

  • Implemented the option to calculate conduction area from the circumference of the connected pipe.
  • Made Kugeler-Schulten correlation available for the Convection element.
  • Implemented second order convection calculation for a Convection element connected to a Node. This allows convection calculations to be done using the mass weighed average upstream temperature of the flow elements connected to the node that the convection calculation is performed on. This functionality should result in faster grid independence for subdivided flow fields such as those used in a reactor geometry.
  • Implemented dispersion for porous flow elements to account for the enhance heat transfer resulting from the disruption of flow in porous media. The dispersion is modelled as increased diffusion heat transfer within the fluid.
  • Implemented length over diameter warning for Dittus-Boelter and two-phase flow applications.
  • Added the Overall convection heat transfer coefficient and Convection coefficient as results for Convection elements.


The following enhancements has been made to the Nuclear components:

  • Second order convection can be specified in the reactor chart.
  • Dispersion can be turned on in the reactor chart.
  • An error will be given when not all reactor ports that are defined in the chart are connected.
  • Added gamma_f0, gamma_m0 and gamma_x0 to the fuel reactivity, moderator reactivity, and Xenon reactivity equations to allow the user to specify a constant offset independent of the prevailing temperatures. 
  • Changed “Cross section x neutron flux” input in die neutronics chart to “Xenon cross section x neutron flux” to clarify the use of the input.
  • Implemented warning that normalized control rod insertion depth when upper or lower limit has been reached.
  • Updated “Reactivity” result description to “Control rod reactivity” to clarify its meaning.
  • Added warning if neutronics parameters such as Normalized Power, Normalized concentrations of neutron precursor isotopes, Normalized concentrations of decay-heat producing isotopes, Iodine concentration or Xenon concentration go negative and are limited to zero.
  • Changed point kinetics error condition to be issued if fission power equal to zero and reactivity greater than the decay neutron fraction, Beta.
  • Updated Kugeler-Schulten calculations to interpolate between Nusselt numbers calculated at Reynolds number = 100 and Nusselt numbers of 4 (at Reynolds number = 0) for Reynolds numbers smaller than 100 to correctly reflect the documented range of applicability of the Kugeler-Schulten correlation.


Implemented the ability to specify a solid material volume for “Solid Nodes”, as seen in Figure 16. This provides the ability to account for the thermal mass of solid nodes in an all solid heat transfer network such as those generated by the nuclear reactor model generating script.
Figure 20- Specify Node Solid Volume


Exposed fluid mixture component count so that it can be used in a script.

Heat Exchanger Component

The Effectiveness input on the Heat Exchanger Primary component, as seen in Figure 21, is now a dynamic input and can be changed during transient simulations. An option has been added to change the two-phase region error that is given when the heat exchanger operates in the two-phase region to a warning, instead of an error. This allows users to use the heat exchanger in the two-phase region if required. The new option can be seen in Figure 22.
Figure 21- Effectiveness Input on Heat Exchanger Primary Component.
Figure 22- Treat Heat-Exchanger in Two-Phase Errors as Warnings Option in Flow Solver.


Turbine chart scaling factors are now a value of 1.0 by default on new charts, as seen in Figure 23.
Figure 23- Turbine Chart Scaling Factors for New Charts.


The following enhancements has been made to fluid mixtures:

  • The capability has been added to specify a mass sink with mass fractions specified to nodes that are internal to a network. This allows for the selective removal of fluid components from a fluid stream to model the action of a filter or membrane. This functionality is not available on boundary or edge nodes as the transfer of mass is an advection problem and boundary conditions cannot be propagated in the opposite direction to the flow.
  • Psychrometric results are calculated for all two-phase non-condensable mixtures featuring Water as the two-phase fluid.


The amount of iterations during steady state that is solved before iterative scripts or data transfers start being executed can now be specified in the Flow Solver settings, as seen in Figure 24. The default value is 6 – meaning that the scripts and iterative items will start executing at iteration 7 of the pressure solver (main iterations).
Figure 24- Iterative Scripts Calculations and Data Transfer Settings in the Flow Solver.


The API now provides users with the ability to create copies of components and links. Several functions have been added to the NetworkBuilder interface in order to facilitate this. These functions are documented in the API help file. Examples of how to use these functions have been added to the “NetworkBuilderScripts” demo project located under Demo Networks on the Flownex® Start Page. The Python example “3. Simple Network Builder” has also been updated to show how to use these functions. This example is available in the Help menu under Python Link.


Added the capability to specify an angle for the Louver parallel and opposed 3V blades damper types.



Fixed problems where Flownex® crashed when a user deleted a project and its sub directories in Windows Explorer, after the project was closed but Flownex® still open.

Container Interface

Fixed a bug where flow still occurred even when the level of the Container Interface was at zero. 

Heat Transfer

Limit the emissivity on the Surface Radiation component to values between 0 and 1. 

Iterative Scripts

Fixed the problem where Iterative Scripts did not start running until a certain convergence has been reached.


Fixed the problem where the Temperature guess value specified on a mass sink results in a flow solver error.


Fixed the bug where the K Calculation dialog sometimes showed inputs from a different pipe.


The Steam/Water trap was not added to a default report, this has been fixed.

Results Layers

Fixed the problem with painting Result Layers when a user has disconnected links, as parts of the network was not shown at all.

Shell and Tube Heat Exchanger and Finned Tube Heat Exchanger

Fixed the Pressure Drop Excluding Elevation Result, as the result changed with number of tubes specified in parallel.

Download full release notes here.

FLOWNEX SE 8.11.1 (2020)

FLOWNEX SE 8.11.1 (2020)
The latest Flownex® SE 2020 Release opens up new possibilities for modelling complete HVAC systems. Exciting new features include an all new ducting components library based on ASHRAE standards, the psychrometric boundary condition and psychrometric chart, flow paths and property graphing, overall performance improvements and much more.  Be sure to have a look at the full list below. Students can also benefit from the new features as the latest Flownex® SE 2020 Student Version is also available to download from our website.



Ducting Components

Many heating ventilation and air conditioning related components, including ducts, transitions, dampers, junctions, combiners, elbows, screens, entrances and exits have been added to the Flownex® component database, as seen in Figure 1. These components allow for easy modelling of HVAC ducting systems in line with the ASHRAE standards.

Fig 1 Ducting Components
Fig 2 Ducting Components used in HVAC Tutorial

Volume Flow Boundary Conditions

The boundary condition specification options have been expanded to include the specification of volume flow boundary conditions, as seen in Figure 3.  The volume flow specification will be used to calculate the equivalent mass flow boundary conditions commensurate with flow conditions.  The thermodynamic condition can be based on the current node conditions or user specified reference conditions.

Fig 3 Volume Flow Boundary Conditions

Psychrometric Boundary Conditions

It is customary in HVAC applications to specify psychrometric boundary conditions for moist air.  A new Psychrometric Boundary Condition is available in the Nodes and Boundaries Library, as seen in Figure 4.

Flownex® now allows for the specification of wet bulb temperature, relative humidity and humidity ratio for moist air mixtures in addition to the psychrometric results that are available for two-phase non-condensable mixtures.  The calculation of wet-bulb temperature has been extended to include frost bulb temperatures. 

A new fluid named Humid Air has been added to the Mixed Fluids in the Master database for use with the Psychrometric Boundary Condition component.

Fig 4 Psychrometric Boundary Condition
Fig 5 Psychrometric Boundary Condtion Inputs

Psychrometric Charts

A psychrometric chart can now be plotted for humid air. The psychrometric chart together with plotted component operating points can assist the user to graphically analyse the psychrometric processes of a system.

Fig 6 Psychrometric Chart

Graphs Through Flow Paths

The ability to plot a property, for example, the total pressure through a network has been added.

The property of components along a defined flow path is plotted.  Flow paths can be defined by selecting the start and end components of the flow path. The context menu can then be used to quickly define a new graph.

Fig 7 Flow Paths in the Results Ribbon
Fig 8 Flow Path Graph

PH Diagram

The option to plot a pressure and enthalpy diagram for two phase fluids has been added, as seen in Figure 8.
The pressure-enthalpy operating point of a component using the Fluid Property Graph can therefore be plotted.

Fig 9 Pressure vs Enthalpy Diagram Option
Fig 10 Pressure Enthalpy Diagram

FMI Master Capability

Further support for the FMI standard was added to Flownex®. Flownex® can now serve as an FMI master for version 2.0 compatible FMUs. It can import both model exchange and co-simulation FMUs. FMUs are added as components in the project library and are used like any other simulation component. These FMUs can be used in both steady state and transient simulations.
Fig 11 FMI Master Capability

Result Layer Improvements

The Result Layers has been updated to show density, energy source, mass source and an indication if choking is present, as seen in Figure 10.

The result layers were also improved to shade the area over the connecting fibres between nodes and elements, which makes it much easier to see the results graphically in large networks.

Fig 12 Improved Result Layers


Performance Improvements

Working with large networks was optimised. Several improvements were made to decrease the time associated with opening large networks and selecting parts of the network. The initial time associated with opening Flownex® has been improved, as well as the time associated with opening networks. The time associated with assigning fluids in large networks has also been improved.

API Improvements

  • Added the ability to create data references through the API. This allows users to create charts such as pump charts, valve charts, etc. by using the API alone.
  • Added a Python example to demonstrate adding charts through the API.
  • Added a demo network example to demonstrate adding charts via C# scripts inside a project.
  • Added Visual Studio 2019 compatibility to the extendibility feature.
  • Made it possible to set the chart and other non-double properties on components using the MATLAB coupling.

Script Editor Improvements

One of the best ways to quickly generate a script is by using a Quick Script component. By using the Quick Script to add all the variables you need and then clicking the show entire script button, you can then copy and paste this code to an ordinary script to customise it further. To make this process easier, buttons and context menu items were added to the script dialog to select and copy script code in the Script Editor.

Intellisense has been added to function scripts like the Pipe Friction Factor script and the Heat Transfer Coefficient calculation scripts.

Search and replace functionality were added to all the script editors. Press Ctrl+F to activate the search dialog or Ctrl+H to activate the Replace dialog.


Fig 13 Copying and Pasting Code in the Script Editor
Fig 14 Example of Intellisense added to Friction Factor Script
Fig 15 Example of Find and Replace Functionality added to Scripts

Quick Scripts

Several additional property types were added to the Quick Script – this include data references, component and property selectors. The primary reason for this was to make it possible to use fluid functions in the Quick Script as well as properties from other components.

Fig 16 Property Types added to Quick Script

Example Scripts

An example script that interpolates on a 4D Generic Chart has been added – this is a good generic way to easily add lookup tables to simulations.

The example scripts were changed so that they are not contained inside compounds anymore. This makes it easier to see the actual script code as well as to modify the scripts. The compound-based example scripts are still available in a category called “Legacy Compound Scripts”, as seen in Figure 17.

Fig 17 Interpolation Script added to Example Scripts

Iterative Scripts

  • The scripts will now only start executing once an initial flow field has been established. This is usually after five iterations depending on the solver settings.
  • A function has been added so that a user can specify whether data transfer should happen after the initialise method and before solving the Flow Solver components.

Parameters Tables

  • The user can now set Data Reference Properties, Integer, Boolean and Option Properties from Parameter Tables.
  • In order to distinguish between Result and Input parameters in a parameter table heading, the results parameters are shown with a darker grey colour.
  • The layout has been improved for Parameter Tables with different DPI screens and custom screen scaling.
  • The Parameter Table active conditions drop down now only shows the first thousand items. This was done to increase GUI performance when using very large Parameter Tables.


When saving details for a server license the Node Locked license details are now reset and vice versa. This makes it easier to switch between Server and Node Locked licenses.


  • Added the ability to change fluid property/characteristic graphs axes units.
  • Added the ability to plot the convection/radiation properties of a Composite Heat Transfer or a Distributed Heat Source along the length of one of the connected pipe components. Previously all points were plotted at the same length.
  • Added borders to graphs. White (hidden) by default.

GIS Importing

Added several new online map sources, as seen in Figure 18.

Fig 18 Examples of Online Map Sources added

FlownexSE Console

The console version of Flownex® can now be used to run parametric studies or sensitivity analysis. The user can specify the command line parameter -sensitivityandparametric to run the current active sensitivity analysis configuration in a project.

Nuclear Reactor

  • The Nuclear Reactor now allows the use of multiple Pebble Bed Fuel Zones in transient cases. Previously the chart based neutronics implementation only worked in transient cases for one fuel zone.
  • Added an error when the sum of fractions for heat input for all the zones in the nuclear reactor does not equal one. For cases when the sum is zero, this will be a warning only.
  • Added toggle buttons to ribbon menu to easily turn on and off result file generation settings, as seen in Figure 19.
Fig 19 Generate after steady state and generate after transient toggle button

Heat Exchangers

Added secondary loss inputs to the primary and secondary side of the Plate Heat Exchanger component.

Solver Properties

  • Added lower limits for the following inputs:
    • Number iteration Temp1
    • Number iteration Temp2
    • Number iteration Temp transient.
  • Changed name of “Use iterative temperature solver” input to “Use BiCG matrix solver for energy equation solution”.
  • Add properties on the Scheduler to indicate if warnings and errors have occurred. These properties can be used in parametric studies etc. to monitor success of solving over all the runs. The warning and error count were also added as properties.

Distributed Heat Source

  • Added the ability to specify the heat input associated with the Distributed Heat Source component using a local specification option.
  • Added errors and warnings for the Distributed Heat Source when incorrectly connecting Distributed Heat Source components to each other or when the Distributed Heat Source is over specified.
  • Fixed problem with heat fractions not being applied during transient for distributed heat source.

Jet Pump Component

Added loss coefficient results to the Jet Pump component.


  • The Momentum addition inputs will now only be available on pipes and not on all components.
  • Implemented warning when small L/D values are used along with Dittus-Boelter and also for two phase flow.

Boundary Condition

  • Added the option to allow the specification of mass source conditions with fixed temperature/enthalpy, hereby allowing energy source calculations that are not based on ambient conditions.

Secondary Loss Component

Extended secondary loss component modelling capability to include Liquid-Gas mixtures, particularly for modelling oil-air mixtures in gas turbine lubrication systems.

Nozzle and Rotating Nozzle

Implemented input area option on Nozzle and Rotating Nozzle components, allowing for non-circular orifice shapes.

Labyrinth Seal

Added results for increments in discretized Labyrinth Seals.

Jet Impingement Convection

Removed upstream cross flow link in Jet Impingement component and instead use net inflow to fluid node. This enables modelling networks with jet impingement where the flow direction of the cross-flow stream is not pre-determined, but forms part of the solution.

Rotor-Stator and Rotor-Rotor

Added disk area results for increments in cavities. This allows more detailed heat transfer modelling and calculating thrust forces.


Added gauge pressure result.

All Element Types

Added humidity ratio result on all elements when used with the Humid Air fluid.

Validation Pack

The following items were added to the  Validation Pack:

Custom Losses
  • Flow Resistance
  • Secondary Loss
  • User Specified Pressure Drop
  • User Specified Pressure Ratio
  • Cross Junction
  • Damper
  • Duct
  • Elbow
  • Entrance
  • Exit
  • Obstruction
  • Transition
Heat Exchangers
  • Finned-Tube Heat Exchanger
  • Plate Heat Exchanger
  • Shell & Tube Heat Exchanger
Heat Transfer
  • Distributed Heat Source
  • External Pipe Heat Transfer


  • Slurry Networks
Nodes and Boundaries
  • Psychrometric Boundary Condition
  • Volume Flow Boundary Condition
  • Nuclear Reactor
  • PBMM
Rotating Components
  • Custom Vortex
  • Forced and Free Vortex
  • Labyrinth Seal
  • Rotating Annular Gap
  • Rotating Nozzle
  • Rotor-Rotor Cavity
  • Rotor-Stator Cavity
Turbos and Pumps
  • Turbine and Compressor
  • Basic Valve
  • Check Valve
  • Control Valve with Loss Coefficient
  • Pressure Regulating Valve
  • Pressure Relief Valve


General Stability

  • When solving was disabled on components a crash happened after solving a second time and then saving the network. Several other actions also lead to a crash after disabling solving on components and then solving the network, which has been fixed.
  • Changed reactor fluid assignment from recursive to non-recursive to avoid a stack overflow for very large reactor sub-networks.


  • Fixed unit for kJ/mol where it appeared as kJ/kmol.

Parameter Tables

  • Fixed problem where the order of columns was not remembered when saving and reloading.
  • Fixed problem when reordering the inputs in a Parameter Table did not reorder the columns correctly.
  • Fixed problems when creating a copy of a parameter table, as the result parameters were changed to input parameters.

Data References

  • When a data reference was not found while loading compounds the way the error was reported made it difficult to pinpoint the source by double clicking on the error. This has been fixed.
  • Implemented a system where dynamic properties of charts gets saved to the project and to the snaps. This is done for charts in all databases. For instance, if scaling factors are changed from the chart property grid they will now be saved correctly.


  • Made CSV export for graphs work with different locales.
  • Fixed incorrect scaling on secondary Y-axes.
  • Added missing flow regime labels on the two-phase flow regime graphs.


  • Fixed the problem where the manual did not contain all the functions in the API.
  • Fixed the problem where constructing compounds using the displayed type name sometimes did not work.
  • Made properties such as Ck, Beta and Alpha of heat exchanger charts editable through API. 

Compound Components

  • Add the ability to drop tooltip properties in the middle of the list when setting up tooltips – they were incorrectly added to the bottom previously.


  • Removed repeat option from actions – it was not used and did not function correctly. Repeating behaviour should rather be implemented using scripts.

GIS Importing

  • Fixed importing for some locales were the comma separator caused problems while retrieving elevations from google.
  • Fixed bug where identifier text etc. were sometimes displayed in reverse.


  • Fixed crash when running Designer etc. and a component that was used as part of the setup has been deleted.


  • Fixed the problem where increments in results did not update immediately on pipes when changing the number of increments.
  • Fixed “micro meter” spelling mistake in the Roughness Editor.
  • Fixed Transient and water hammer related results category wording on pipe.
  • Added convergence check for choking with unrealistic short pipe lengths in two-phase flow. In such cases the solution might have appeared to be converged, but actually required more iterations to accurately determine whether the choke point is reached or not.

Nuclear Reactor

  • Fixed the problem where an error was issued with the General Fuel Zone due to a material not being assigned when it should not be issued.
  • Fixed problem where reactors using the same neutronics chart gave the same results no matter what inputs were specified.
  • Fix problem where if you clicked in Top Height field for a row in the advanced reactor and it was negative, where the user needed to terminate Flownex to continue.
  • Several fields did not commit their data correctly in the editors for the Advanced Reactor.
  • Updated fractional heat assigned to subdivided zones.
  • The horizontal and vertical permeabilities are now correctly applied to the various zone types.
  • Convection heat transfer results were updated to include all flow convection flow paths for pebble bed and general fuel zones—this does not impact the solution.
  • Fixed error in the calculation of maximum moderator temperatures for general fuel zones.
  • Addressed code issue when a permeability value of zero was set to a solid with 1D vertical flow zone.
  • Fixed reactivity output units.
  • Added warning when user supplies a zero hydraulic diameter corresponding to a non-zero permeability.
  • A default value of 1 has been assigned to the heat fraction, and coefficient 0 of the axial and radial power profiles on the power distribution dialog.
  • Fixed sub-zone mass flow units.
  • Fixed an error in the height assignment of a single cavity that is in a sub-divided row.
  • Fixed Pebble Bed flow node volumes when DW friction losses are selected.
  • Added convection and conduction areas, length and height outputs in *.arr file.
  • Added porosity to the Reynolds number calculation to correctly use the local superficial velocity in the Kugeler-Schulten pressure drop correlation.
  • Changed friction factor result for packed bed flow elements so that it is based on the actual velocity and not the superficial velocity.
  • Changed static pressure calculation to use actual (not superficial) velocity for pebble bed elements with non-zero solid fractions.

Version Upgrading

  • Fixed upgrade of Cooling Orifice to Nozzle – fixed the transfer of area, number in parallel and Cd value.
  • Decreased the time of upgrading a Flownex project file to a newer version – some unnecessary files were checked during upgrading.
  • Fixed upgrade of compounds that contained some of the fields used in H calculation and Primary loss calculation.

Rotating Components

  • Disabled inputs on Rotor-Rotor and Rotor-Stator that are set from the Cavity Editor when using the Cavity Editor tool.
  • Fixed problem where the axial measurement of gap width and shroud used the radial measurement in the cavity editor.
  • Fixed static enthalpy calculation for reverse flow in Rotating Channel and Rotating Nozzle.
  • Changed Daily & Nece correlation in cavities to use outer radius for density and viscosity in Reynolds number definition.

Rotating Components

  • Fixed upgrade of Cooling Orifice to Nozzle – fixed the transfer of area, number in parallel and Cd value.
  • Decreased the time of upgrading a Flownex project file to a newer version – some unnecessary files were checked during upgrading.
  • Fixed upgrade of compounds that contained some of the fields used in H calculation and Primary loss calculation.

Heat Exchangers

  • Fixed heat exchanger components that should not allow heat transfer to them from other components via generic heat transfer components.
  • Fixed elevation input for Cooling Tower and Bulk Air Cooler.
  • Fixed surface temperature result for Plate Heat Exchanger primary and secondary not showing correct results.


  • Fixed problem with enthalpy and viscosity being incorrectly reported in writing out data from material test dialog.
  • Report fluid type correctly in writing out of data from material test dialog.
  • The option was removed to specify the specific heat for fluids in a script.
  • If enthalpy is specified in a script and no inverse function is defined a Newton Raphson is done to determine temperature from enthalpy.
  • Fixed the calculation of enthalpy from the option where specific heat is specified as polynomial equation that resulted in unrealistic temperatures on account of the enthalpy being capped instead of extrapolated when used out of range.


  • Fixed problem where the direction of drawing influenced results on Butterfly Valves.

Turbo Machinery

  • Fixed showing of speed options with enabling and disabling of Shaft links on Basic Centrifugal Pump.
  • Fixed Simple Turbine tooltip not showing.
  • Plot head excluding elevation on operating point plots so that they are shown correctly on pump curve.
  • Improved speed line extrapolation in turbo machine charts to use an average gradient calculated between the two closest speed lines, instead of allowing this gradient to change over the reach of the mass flow axis. This leads to much more realistically shaped extrapolated speed curves, with corresponding improvement in solver convergence.

Steam Turbine Group Efficiency

  • Changed warning for Steam Turbine Group Efficiency calculation, in the event that the pressure is outside of the validity range, to be issued only for the governing stage where it is applicable.


  • Tooltip added to Friction Loss and Motor/Generator components.

Heat Transfer Coefficients

  • Fixed upper limit Rayleigh number warning for free convection coefficient correlation over a horizontal cylinder to be 1e12 instead of the previous incorrect value of 1e13.
  • Implemented non-zero lower limits for laminar and turbulent friction factors.
  • Rounded Gr and Ra numbers reported in warnings to reduce duplication of warnings.

Secondary Pressure Loss Component

  • Fixed Secondary Pressure Loss choked flow calculation when flow area is different from choking plane. The choking plane is now calculated (either upstream area, downstream area or element flow area), and not assumed to be coincident with the element flow area.

Boundary Conditions

  • Added warning when a mass source is specified without associated temperature specification.

Hydraulic Grade line and Energy Line Results

  • Changed hydraulic grade line and energy line results to use gauge pressures and not absolute pressures. This is more consistent with typical industry application where these results are used frequently, such as slurry flows.

British Standard Orifice

  • Removed choking result from British Standard Orifice since it is not applicable.

Composite Heat Transfer Elements

  • Added warnings when incremented Composite Heat Transfer components are connected to non-incremented heat transfer components resulting in a mismatch in the number of increments.
  • Changed solid node temperature result with multiple increments to reflect averaged temperature of the surface.

Flow and Solid Nodes

  • Fixed flow node Heat source result that incorrectly displayed twice the user specified heat input under some configurations.
  • Fixed Solid Nodes incorrectly displaying inputs for radial pressure boundary and trace elements.

Flow Resistance

  • Fixed Flow Resistance square root input option that did not converge for reverse flows.

Open Container and Vented Container

  • Changed steady-state behaviour for Open and Vented Container to issue an error after the solution is done and there is flow exiting from above the level in the container. Previously a check valve was activated during the solution process, but this gave rise to diverging solutions.

Incremented Elements

  • Fixed incremented elements not updating incremented node elevations correctly when connected to tanks and containers.
  • Fixed incremented elements not updating incremented nodes swirl properties correctly when these elements are specified to rotate at machine speed.

Download full release notes here.

FLOWNEX SE 8.10.0 (2019)

FLOWNEX SE 8.10.0 (2019)

Flownex® SE 2019 is pushing the boundaries of thermal fluid system simulation.

We’ve added a few new enhancements and additions, including improvements to our heat exchangers, a custom vortex as well as a whole new appearance and functionalities to our graphs. We’ve also updated a few of our components to allow liquid-gas mixture fluid types.
A NEW student version 2019 is also available to download. 



Adaptive Timestep

Fig. 1 - Adaptive Time Step in Scheduler
An adaptive timestep functionality has been added to the Flownex® solver that automatically refines the timestep size through a transient simulation. This results in small timesteps when fast transients (such as pressure pulses during water hammer) are occurring to accurately predict the solution and larger timesteps when possible to effect shorter solving times. This feature monitors the pressure, energy, mass flow and density of all the components and will automatically reduce the timestep to ensure that the solution remains within the specified accuracy criteria. This allows the user to accurately predict fast transients such as pressure pulses without having to perform a temporal convergence study first. For more information about how the adaptive timestep algorithm is implemented, please refer to the Scheduling chapter of the General User Manual. A button has been added to the toolbar that gives the user quick access to the time step settings. It is located next to the Reset Time button in the Simulation Control section, as seen in Figure 2.
Fig. 2 - Time Step Settings

Cavity Editor

The inputs of the Rotor-Rotor and Rotor-Stator components have been significantly enhanced in order to allow a user to easily specify a complex geometry for the cavity.

The complex geometry can be specified by using the Cavity Editor, which opens when double clicking on a Rotor-Rotor or Rotor-Stator component. The Cavity Editor allows the user to import a background picture for the cavity. The geometry and dimensions can then be defined on the picture in the Cavity Editor, as seen in Figure 2.

Fig. 3 - Rotor-Stator Cavity Editor - Reference Measurements

After a picture has been imported, the user can define the dimensions of the cavity by specifying two points at any location on the drawing. Thereafter, the rotor and stator surface geometries are easily drawn on top of the picture.

Fig. 4 - Rotor-Stator Cavity Editor - Rotor Surface Geometry

Other geometric items like the position of bolts, gap and shroud width, as well as defining the discretization is also done easily using this Cavity Editor.

Fig. 5 - Rotor-Stator Cavity Editor - Discretisation

Custom Vortex

Fig. 6 - Customer Vortex Component
A Custom Vortex component has been added to the Rotating Components Library. The custom vortex is a vortex model commonly used in gas turbine cavity modelling. The tangential velocity is specified to produce a velocity profile between that of a forced vortex and free vortex. The radial velocity profile is specified in the following format Cθ= s⋅rn. A custom vortex is characterised by a swirl constant, s, and a vortex weighing factor, n. The custom vortex model provides a simplified cavity model that allows the user to adjust the swirl constant and vortex weighing factor to match the swirl pressure rise seen in empirical measurements.

Heat Exchanger Improvements

The Heat Exchanger components in Flownex® has been updated. These components are now easier to use and a few essential features have been added. The heat exchangers that has been updated is the Shell and Tube Heat Exchanger, Finned Tube Heat Exchanger and the Recuperator, which has been renamed to a Plate Heat Exchanger. The changes make using the heat exchangers for a general application like radiators etc. simpler. Furthermore, fouling factors and fin efficiencies have been added to the heat exchangers where relevant. These can be used to model degradation over time and changes in the condition of the heat exchangers.

Shell and Tube Heat Exchanger

Cosmetic Changes

New icons have been added for the Shell and Tube heat exchanger and the names now clearly indicate the shell side and the tube side.

Fig. 7 - Shell & Tube Heat Exchanger
Input Changes
Shell Side Primary Loss Calculations

The shell side supports specification of the friction factor through a constant value, using a script or using a Fanning friction chart. By default, the Fanning friction factor chart is used. The user can however easily use a correlation from another source in the script defined friction factor specification. These options can be seen in Figure 8.

Fig. 8 - Shell Side Primary Loss Options
Shell Side Heat Transfer Coefficient Calculation

The shell side now supports built in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, the Shell Side heat transfer coefficient calculation correlation is used. The user can however easily use a correlation from another source in the script defined heat transfer coefficient calculation, as seen in Figure 9.

Fig. 9 - Shell Side Convection Coefficient Options
Tube Side Primary Loss Calculation

The tube side supports specification of the friction factor through a constant value, Darcy Weisbach correlations, using a script or using a Fanning friction factor chart. By default, the Darcy Weisbach correlation is used, as seen in Figure 10.

Fig. 10 - Tube Side Primary Loss Options
Tube Side Heat Transfer Coefficient Calculation

The tube side supports built in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts, as seen in Figure 11. By default, the Gnielinski correlation is used for the tube side heat transfer coefficient calculation.

Fig. 11 - Tube Side Convection Coefficient Options
Finned Tube Heat Exchanger
Cosmetic Changes

New icons have been added for the Finned Tube heat exchanger and the names now clearly indicate the fin side and the tube side.

Fig. 12 - Finned Tube Heat Exchanger
Input Changes

Fin Side Geometry

A simplified set of inputs has been added to specify the geometry of a rectangular finned tube heat exchanger with round fins. This is the default option now, as seen in Figure 13.

Fig. 13 - Rectangle HX with Round Fins Inputs

The user now specifies more readily available geometric parameters like the heat exchanger width height and length as well as tube and fin diameters. The older more generic specification is still available.

Fin Side Primary Loss Calculation

The fin side supports specification of the friction factor through a constant value, using a script or using a Fanning friction factor chart. By default, the Fanning friction chart is used. The user can however easily use a correlation from another source in the script defined friction factor specification.

Fin Side Heat Transfer Coefficient Calculation

The shell side now supports script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, Stanton Prandtl chart is used. The user can however easily use a correlation from another source in the script defined heat transfer coefficient calculation.

Tube Side Primary Loss Calculation

The tube side supports specification of the friction factor through a constant value, Darcy Weisbach correlations, using a script or using a Fanning friction factor chart. By default, the Darcy Weisbach correlation is used.

Tube Side Heat Transfer Coefficient Calculation

The tube side supports built in correlations for the heat transfer coefficient calculation, as well as script defined heat transfer coefficient calculation, constant value specification and Stanton Prandtl charts. By default, the Gnielinski correlation is used for the tube side heat transfer coefficient calculation.

Plate Heat Exchanger
Cosmetic Changes

The Recuperator heat exchanger has been renamed to the Plate Heat Exchanger, which describes the functionality of the heat exchanger better. New icons have been added for this heat exchanger too.

Fig. 14 - Plate Heat Exchanger