Objective:
Learn how to set up and run a Conjugate Heat Transfer (CHT) analysis in nTop. This feature extends the standard Flow Analysis by coupling fluid flow with solid heat conduction. In this guide, we will use a Heat Sink example to demonstrate how to simulate cooling performance by analyzing the interaction between an airflow channel and a solid aluminum heat sink.Applies to:
- nTop 5.38 or later (requires nTop Fluids capabilities).
Procedure:
- Prepare Your Geometry: Before starting, ensure you have implicit bodies defined for both your fluid and solid regions.
- Solid Geometry (Heat Sink): The physical parts that conduct heat, such as the heat sink base and fins.
- Fluid Geometry (Air Channel): The negative space or volume surrounding the heat sink where the air flows.
- Set Up the Virtual Model: We need to add a Simulation Model block to act as the container for your simulation setup. You will use its “Virtual Model” overload, which is designed for LBM-based simulations that do not require traditional body-fitted meshing.
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Add the Fluid Domain (Air):
- Add a Fluid Domain block to your Virtual Model list.
- Input your Fluid Domain implicit body as the Body input (the air channel).
- Define the Fluid Attribute using the Air block (or an Isotropic Material: Isotropic Fluid Property (Kinematic Viscosity) and Isotropic Thermal Property (Conductivity and Specific Heat).
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Add the Solid Domain (Heat Sink):
- Add a Solid Domain block to the same list.
- Input your Solid Geometry (the heat sink body).
- Define the Solid Attribute using an Isotropic Material (e.g., Aluminum) that includes Isotropic Thermal Property values.
Note: Both materials must have thermal properties defined to enable the CHT solver.
- Define Boundary Conditions: Input a list of boundary conditions into the Flow Analysis block. For CHT, you need to define both flow and thermal conditions on the relevant CAD faces or boundaries.
Note: You need at least one Temperature Restraint to enable CHT.
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Flow Conditions:
- Inlet: Add a Velocity boundary (e.g., 1 m/s) to the face where air enters the channel.
- Outlet: Add a Pressure boundary (e.g., 0 Pa) to the face where air exits.
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Thermal Conditions:
- Inlet Temperature: Add a Temperature boundary to the inlet face (e.g., 298 K or 25°C) to define the incoming air temperature.
- Heat Source: Add a Surface Heat Flux boundary to the bottom face of the heat sink base. This simulates the heat load from a chip or electronic component (e.g., 2000 W/m²).
Note: nTop Fluids automatically handles the heat transfer interface between the fluid and solid domains defined in your Virtual Model. Any wall or boundary not explicitly assigned a thermal boundary condition is treated as having a zero-temperature gradient. This means the solver assumes these surfaces are perfectly insulated, and no heat is conducted across them.
- Configure the Flow Analysis Block
- Model: Input the Simulation Model containing both the Air and Heat Sink domains.
- Boundary Conditions: Input the list of flow and thermal boundaries created in Step 3.
- Cell Size: Define the resolution of the Cartesian grid (e.g., 5mm).
- Run the Simulation: Run the Flow Analysis block.
- Visualize Results: Once the analysis is complete, you can inspect the thermal performance.
- Temperature Fields: Switch the HUD variable to Temperature time-averaged to view the heat distribution on the solid fins and in the surrounding air.
- Display Mode to Streamlines: Visualize the airflow path and color the streamlines by Temperature to see where the air picks up heat.
- Surface Plot: Use the temperature time-averaged field to plot colour onto the implicit body to visualise the values and view them in Section Cut (X) mode.
