Heat Exchanger with Fluid Flow Model

Given: Two flow channels and a metallic plate have the same height of H = 0.1 (m) and length L = 1 (m). The two end surfaces of the plate are also adiabatic. Hot fluid enters channel #1 at a fixed temperature T1 and mean velocity U1. Cold fluid enters channel # 2 at a fixed temperature T2 and mean velocity U2. Heat exchanges through the center metallic plate.

T₁ = 800 K

U₁ = 0.2 m/s

T₂ = 300 K

U₂ = 0.1 m/s

Material Properties

Fluid

• Mass density: r = 1000 (kg/m³)
• Thermal conductivity: k = 10 (J/s/m/K)
• Specific heat: C_p = 25 (J/kg/K)
• Viscosity: m = 0.15 (kg/m/s)

Solid

• Mass density: r = 8000 (kg/m³)
• Thermal conductivity: k = 50 (J/s/m/K)
• Specific heat: C_p = 500 (J/kg/K)

Find: The temperature distribution through the cross section of the heat exchanger.

This example only covers creating the model. For instructions on setting up and performing the analysis, see Heat Exchanger with Fluid Flow.

There are two options for solving this model. The fluid and thermal analyses can be coupled (both analyses solved simultaneously), or they can be uncoupled (each analysis solved individually). Since the fluid is forced through the model, buoyancy effects are negligible, so use the uncoupled approach (also a faster solution).

• Perform one fluid flow analysis in Design Scenario 1. The analysis includes both fluids but not the solid metallic plate. (To ensure that the complete mesh is satisfactory, we will mesh all three parts in this Design Scenario.) Both fluids will be on part 1 and the solid will be on part 2.
• Perform a steady-state heat transfer analysis in Design Scenario 2. This analysis  includes all three regions: the two fluids and the metallic plate.

Use 2D elements for this analysis. The mesh must be created in the YZ plane.

1. Start a new FEA model.
   1. Set the analysis type to Fluid Flow: Steady Fluid Flow.
   2. Set the unit system to be consistent with the problem statement. Click Override Default Units and select the Metric mks (SI) from the Unit System drop-down menu. This sets everything we want except for the temperature. Change the Unit System to Custom and set the Temperature (Absolute) to K(K). Click OK to set the units.
   3. Click New and enter a model name.
2. For the best results, we want to create a structured mesh that is fine near the fluid/solid interfaces and the outer edge of the fluid. We can do this using a 4-point rectangular mesh with a geometric spacing. First, create a mesh that represents half of the thickness of the cold fluid. Select Mesh Structured Mesh 4 Point Rectangular.
3. Type 6 in the AB field for the number of divisions through half of the thickness. Type 80 in the BC field for the number of elements along the length. Click the button next to the AB  field. Click the Geometric  button. Set the Ratio field to 3 and click OK. Define Point A as (0,1,0), Point B as (0,1, 0.05), Point C as (0,0,0.05) and Point D as (0,0,0). Click Apply to create the mesh. These points place the centerline of the fluid parallel to the Y axis at Z=0.05 m.
4. Click the X button to close the Point Mesh Setup dialog.
5. To see the complete model, change the view using View Navigate Orientation Right View.
6. Mirror the mesh to create the other half of the fluid. Use Selection Select Lines and Selection Select All to select all the lines in the model. Select Draw Pattern Mirror. The mirror plane does not exist, so click New to define the mirror plane. Set the  Plane  to XY and activate Use Offset. Set the offset to 0.05. Click OK to finish creating the mirror plane. Click OK to perform the mirror operation.
7. Create a copy of the cold fluid mesh for the hot fluid. Select all the lines in the model and select Draw Pattern Move or Copy. Activate the Copy check box. Type 0.2 in the Total distance field and select the DZ button. Click OK.
8. It is not necessary for the solid to have as fine of a mesh as the fluid. Since the four  corners of the solid are defined by the fluid, select Mesh Structured Mesh 4 Point Rectangular. Set the Part to 2.Type 8 in the AB field for the number of divisions through the thickness. Make sure 80 is in the BC field for the number of elements along the length. Click the button next to the AB field. Select the Constant button and  click OK. Click the four corners, starting with the bottom left corner of the plate and continuing clockwise. (Points A and B define the thickness of the plate.) Click Apply to create the mesh.
9. Click the X button to close the Point Mesh Setup dialog box.
10. Click anywhere in the display area away from the model to cancel the lines selections. A red mesh (part 2) sandwiched between two green meshes (part 1) displays.