Validating PCHE Model in Fluent: Addressing Pressure and Periodic Boundary Conditions

 Validating Printed Circuit Heat Exchanger Model in Fluent

This response addresses your questions regarding pressure and boundary conditions in your Printed Circuit Heat Exchanger (PCHE) model validation using Fluent:

Question 1: Operating Pressure and Boussinesq Parameters

Pressure:

• You cannot directly set two different operating pressures in Fluent for a single-phase flow domain.

• Since water operates at a much lower pressure than CO2, using 101325 Pa (atmospheric pressure) as the operating pressure is a reasonable simplification.

• This assumes the pressure difference between the streams is negligible compared to the absolute pressure of CO2.

• You can define the pressure difference between the inlet and outlet of each stream using a "Pressure Outlet" boundary condition with a "Gauge Pressure" specification. Here's how:

  • CO2 Outlet: Set the gauge pressure to 7.398675 MPa (accounts for the pressure drop across the channel).
  • Water Outlet: Set the gauge pressure to 0 Pa (atmospheric pressure).

Boussinesq Parameters:

• Since your model operates at a constant pressure (atmospheric for water and a slight increase for CO2), buoyancy effects likely have a minimal impact.
• You can disable the Boussinesq approximation by setting the "Density Variation" option to "No" in the "Species" menu for both water and CO2.
• Alternatively, you can define a constant density value for each fluid based on their average temperature within the channel.

Question 2: Periodic Boundary Conditions

Verification:

Unfortunately, I cannot directly assess your attached JPEG file. Here's how to verify the application of periodic boundary conditions:

1. Go to the "Boundary Conditions" panel in Fluent.
2. Select the top/bottom and left/right walls where you want to apply the periodic condition.
3. Set the "Type" to "Periodic."
4. Under the "Periodic Conditions" tab, you'll see options for:
   • Upstream Bulk Temperature: Leave this blank for a wall (not applicable).
   • Flow Direction: This specifies the flow direction relative to the selected face. For opposite faces in a periodic condition, set them to opposite directions (e.g., "In" and "Out").
   • Pressure Gradient: Leave this blank for a wall (not applicable).

Additional Tips:

• Ensure the mesh on the opposing faces is well-matched and aligned for proper flow continuity through the periodic boundaries.
• You can monitor convergence to verify if the periodic conditions are applied correctly. Ideally, the solution variables (e.g., temperature, pressure) should match across the periodic interfaces.

By following these steps and considering the limitations of single-phase modeling for pressure differences, you can improve the setup of your PCHE model in Fluent.