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.