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Heat Transfer

Conjugate Heat Transfer

Introduction

This is an example of heat transfer analysis including heat conduction in a solid. It is computed with a multi-region method consisting of two regions: solid and fluid. The solver uses chtMultiRegionSimpleNFoam developed by NextFoam.

A circular fluid region is surrounded by a rectangular solid region. The fluid region has a rotating rod and uses MRF. The temperature of the rod is 373 K, and gravity acts in the -y direction.

The calculation conditions are as follows

solver : chtMultiRegionSimpleNFoam
turbulence model : \(Standard\) \(k-\epsilon\)
material properties of fluid
- density : Perfect Gas
- viscosity : 1.79e-5 \(kg/ms\)
- thermal conductivity : 0.024 \(5W/mK\)
- heat capacity(Cp) : 1,006 \(J/kg\)
material properties of solid
- density : 1,900 \(kg/m^3\)
- thermal conductivity : 0.016 \(W/mK\)
- heat capacity(Cp) : 1,004 \(J/kg\)

Start BaramFlow and load mesh

Run the program and select [New Case] from the launcher. In the launcher, select [Pressure-based] for [Solver Type] and [None] for [Multiphase Model].

Use the given polyMesh folder. In the top tab, click [File]-[Load Mesh]-[OpenFOAM] in that order and select the polyMesh folder.

General

Set gravity of y direction as -9.81.

Model

For this example, we'll use \(Standard\) \(k-\epsilon\) model for turbulence.

Energy is automatically set to include when the Multi-region lattice is read.

Materials

For this example, we will use the materials Air and Solid.

Materials defaults to Air, and click the (+) button to select and add a random Solid.

Set material Properties of Air and Solid as follows

Air

Density : Perfect Gas
Specific Heat capacity \(C_p\) : 1,006
Viscosity : 1.79e-05
Thermal Conductivity : 0.0245
Molecular Weight : 28.966
Absorption Coefficient : 0.0

Solid

Density : 1,900
Specific Heat capacity \(C_p\) : 1004
Thermal Conductivity : 0.016
Emissivity : 0.039

Absorption Coefficient and Emissivity are not used because radiation is not considered.

Cell zone Conditions

Double click fluid region and set select [Materials] as air.

Double click solid region and select [Materials] as solid.

Double click rotor of fluid region and select MRF and set values as follows

Rotating Speed (RPM) : 100
Rotation-Axis Origin : (0, 0, 0)
Rotation-Axis Direction : (0, 0, 1)

Boundary Conditions

Set the boundary type and values as shown below.

fluid_to_solid : Thermo-Coupled Wall(because fluid_to_solid and solid_to_fluid is at the same position, they mush be [Coupled Boundary])
- Coupled Boundary : Region1:solid_to_fluid

inner-wall : wall
- Velocity Condition : No Slip
- Temperature : Constant Temperature
- Temperature : 373 (K)

external-wall : wall
- Velocity Condition : No Slip
- Temperature : Convection
- Heat Transfer Coefficient (\(W/m^2 K\)) : 4
- Free Stream Temperature : 280 (K)

frontAndBackPlanes : Empty

Numerical Conditions

In this example, we'll change the settings as shown below.

Pressure-Velocity Coupling Scheme : SIMPLE
Discretization Schemes
- Pressure : Momentum Weighted Reconstruct
- Momentum : Second Order Upwind
- Energy : Second Order Upwind
- Turbulence : First Order Upwind
Under-Relaxation Factors : use default values
Convergence Criteria : use 1e-6 for Energy and fefault value for the rest

Monito

Monitor the Area-Weighted Average Temperature of the fluid_to_solid surface.

On the Monitoring tab, click Add - Surfaces and set it up as shown below.

Initialization

Initialization is set for fluids and solids separately. You can set the initialization for fluid and solid separately by selecting the tabs at the bottom.

fluid

Velocity : (0 0 0) (m/s)
Pressure : 0 (Pa)
Temperature : 350 (K)
Turbulence
- Scale of Velocity : 1 (m/s)
- Turbulent Intensity : 1 (%)
- Turbulent Viscosity Ratio : 10