Documentation

Conjugate Heat Transfer Analysis

The analysis type Conjugate heat transfer (CHT) allows for the simulation of heat transfer between Solid and Fluid domains by exchanging thermal energy at the interfaces between them. Typical applications of this analysis type exist as, but are not limited to, the simulation of heat exchangers, cooling of electronic equipment, and general-purpose cooling and heating systems.

Water heating up as it passes through a heat exchanger and extracts heat from the air flowing in the opposite direction.
Natural convection around a heat exchanger

Simulation Setup

The following section will explain step-by-step how to set up a conjugate heat transfer (CHT) simulation within the SimScale platform.

Global Settings

Under analysis properties, the turbulence models and the time dependency of the simulation are selected.

Turbulence Model

The following turbulence models are currently supported for conjugate heat transfer analyses:

  • Large-eddy simulation (LES)
    • Smagorinsky

Time Dependency

The time dependency setting determines if the simulation should be solved as a steady-state or transient case.

Find further information about the global analysis settings here.

Geometry

When performing a conjugate heat transfer analysis, additional requirements when preparing the CAD model have to be taken into account. Those requirements include the necessity for the model to contain at least one flow region, as well as properly defined interfaces between contacting regions. (Note: A region is defined as a closed volume; i.e., a (solid) part in your CAD model)

Flow Volume

The simulation domain needs to contain multiple regions with at least one each assigned as solid and fluid domains. In case your raw geometry doesn’t include the fluid domain yet, consider using the flow volume extraction tool.

Via flow volume extraction, it’s possible to only extract or to add an additional flow volume from/to your model.

Interfaces

Interfaces are required for simulating heat transfer between two regions. When creating a conjugate heat transfer simulation or when assigning a new simulation domain to an existing simulation, all interfaces will automatically be detected by the platform. It is required that these interfaces are defined by two congruent faces on both contacting regions. In case this requirement is not met by the assigned CAD model, the platform will recommend an automatic Imprinting operation, which splits existing faces into multiple parts in order to guarantee perfect overlaps.

illustration of imprinting operation
Illustration of the effect of an imprinting operation. For proper contact definition in CHT simulations, it’s required that contacting faces are congruent. If this criterion is not met, the imprinting operation cuts existing faces into smaller parts in order to guarantee perfectly overlapping contacts.

Mesh

multi-region mesh is required to have a clear definition of the interfaces in the computational domain. Find further information here.

Contacts

As mentioned above, all possible interfaces will automatically be detected upon simulation creation and domain assignment. Find out more here.

Model

Under ‘model’, the gravity can be defined. In case LES Smagorinsky has been set as a turbulence model,  its cutoff length can be defined in the model settings panel. Find further information here.

Material

For CHT simulations at least one fluid and one solid domain each are required. Find further information here.

Initial Conditions

Initial conditions define the values which the solutions fields will be initialized with. They play a vital role in the stability and computing time of the simulation.

For CHT analyzes, the velocity, temperature, and pressure fields can either be initialized uniformly or separately via  Subdomains for each region.

Important

It is recommended to set the initial conditions close to the expected solution to avoid potential convergence problems.

Find further information here.

Boundary Conditions

Boundary conditions define the external input parameters for the simulation. A standard boundary condition setup consists of:

  • Velocity inlet(s)
  • Pressure outlet(s)
  • Wall (with heat flux) OR a power source (see advanced concepts below)

Find further information here.

Important Information

In case no boundary condition is assigned to some face/faces, by default these faces will be assigned a no-slip wall boundary condition, and zero gradient for temperature.

Advanced Concepts

Find additional setup options, such as Power sources, Momentum sources, and Thermal resistance networks in the advanced concepts settings panel. Find further information here.

Numerics

Numerical settings play an important role in the simulation configuration. Set correctly, they enhance the stability and robustness of the simulation. In most cases, the standard settings should be acceptable, and should not be changed without reason. Find further information here.

Simulation Control

The Simulation Control settings define the general controls over the simulation. In these settings the number of iterations, simulation interval, timestep size, and several other variables can be set. Find further information here.

Result Control

Result Control allows users to define additional simulation result outputs. Each result control item provides data that requires additional calculation. Find further information here.

Tutorials & User Guides

Take a look at the following tutorial to get started with conjugate heat transfer analysis on SimScale:

Solver

The conjugate heat transfer simulations use the following OpenFOAM® solvers:

  • chtMultiRegionFoam
    For transient simulations with laminar or turbulent flow. This solver uses the PIMPLE method for iterative solution.
  • chtMultiRegionSimpleFoam
    For Steady State simulations with laminar or turbulent flow. This solver uses the SIMPLE method for iterative solution.

Disclaimer

Conjugate heat transfer analysis is performed using OpenFOAM software. See our third-party software section for further information.

This offering is not approved or endorsed by OpenCFD Limited, the producer of the OpenFOAM software and owner of the OPENFOAM® and OpenCFD® trademarks. OPENFOAM® is a registered trademark of OpenCFD Limited, the producer of the OpenFOAM software.

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