Flownex can take into account the following heat transfer simulations:
- Cooling and heating effects of fluids on pipe and component walls.
- Heat lost through the piping, components and housing walls to atmosphere.
- Thermal inertia and heat capacitance of fluids and materials during transient events.
- Heat lost or gained due to changes in atmospheric temperatures.
- Heat transferred by fluids through the walls and plates in heat exchangers.
- Heat lost by pipes submerged in water, insulated pipes, pipes open to atmosphere, etc.
- Optimal Insulation of piping, components and housings.
- Heat added to fluid within solar heating systems.
Within Flownex heat transfer can be simulated on multiple levels to ensure real world scenarios. An example of this could be hot water flowing through a stainless steel pipe with 3 layers of various insulation materials in icy cold atmospheric conditions on a sunny arctic day.
To accurately simulate the heat loss from the hot water in an insulated pipe to the cold atmospheric conditions the following is taken into account in Flownex:
There is heat loss from the hot water to the stainless steel pipe through convection, then conduction heat loss and thermal inertia through the stainless steel pipe and all the layers of insulation. On the outside of the insulation heat is lost through convection to the atmosphere. To accurately simulate the heat loss it all needs to be taken into account in the simulation, it is also possible to simulate radiation heat transfer which will be the heat added due to solar radiation on the outer layer of insulation.
Heat Transfer Phenomena Taken into Account
The Joule Thomson effect describes the temperature change of a real gas or liquid when it is allowed to freely expand through an orifice or a valve under adiabatic conditions. Therefore the fundamental approach in Flownex allows the user to predict accurate and realistic downstream temperatures of a tank blowing off through a valve for example; taking the severe temperature drops into account that may occur.
Buoyancy Driven Flow and Natural Convection
Buoyancy driven flow is a mechanism, or type of heat transport in which the fluid motion is not generated by any external source (like a pump, fan, suction device, etc.) but only by density differences in the fluid occurring due to temperature gradients.
Thermal Inertia and Heat Capacitance
The ability of a material to store heat is called thermal or heat capacitance. When the fluid temperature change that is in contact with that material, the material temperature will not abruptly change towards the new gas temperature (due to thermal inertia). Thermal inertia is a combination of thermal capacitance and the conductivity of the material to conduct the stored heat towards a lower or higher temperature of a fluid in contact with the material.
With the ability to accurately simulate thermal inertia and heat capacitance, Flownex allows users to predict system behavior and system response accurately.
Heat Transfer Types and Typical Applications:
Conduction Heat Transfer
Conduction is the transfer of heat by direct contact of particles of matter, therefore conduction will be the heat transfer through solids, Flownex takes both axial and radial (full two dimensional and even three dimensional) conduction into account and extensive libraries are available of Material types.
Typical uses for conduction heat transfer could be: Insulation requirements to ensure optimal heat is retained in a system, determine heat loss through piping walls to determine if insulation is required, determine rate at which heat will be lost during transient events such as loss of flow in heat exchanger piping, accurate simulation of thermal inertia of system simulation during dynamic simulation, housings, components from atmosphere in a system, heat transferred between plates and walls in heat exchangers, etc.
Convection Heat Transfer
Convection is the transfer of thermal energy by the movement of molecules from one part of the material to another, therefore convection can be considered as heat transfer from a solid surface to a fluid.
Typical uses for convection heat transfer could be, surface cooling or heating caused by fluid flow over a specific section, temperature change of liquids and gasses in heat exchangers, heat lost or gained by fluids in a system, temperature of solid metal surface in a heat exchanger in contact with two different fluids, etc.
Radiation Heat Transfer
Radiation is the transfer of heat energy through empty space. Therefore radiation is heat transferred between two solid surfaces or from a gas to a solid surface.
Typical uses for radiation heat transfer could, solar heating systems, effect of radiation from flames within a furnace to the water walls, radiation in a combustion chamber, etc.
Heat Transfer and Basic Heat Transfer Elements:
The purpose of a Basic heat transfer element is to create very basic heat transfer elements that can be used as the building blocks to simulate more complex heat transfer elements.
For example the Flownex heat transfer (HT) element allows the user to specify conduction in two directions, convection and radiation all in one component. The same heat transfer element functionalities can be built up of a basic conductive, cross conductive, convection and a radiation heat transfer elements. Using the individual components enables users to even model solid material conduction in 3 dimensions similar to finite volume CFD applications.
The HT element can consist of a number of material layers, each of which can be divided into a number of increments. Heat Transfer elements can have both thermal resistance and thermal inertia and can be connected to any components or sections of a fluid simulation component.