Step 7: Boundary Conditions

Boundary Conditions

1.   Set the boundary conditions at the cold inlet ( velocity-inlet-5).

Boundary Conditions velocity-inlet-5 Edit...

Hint:   If you are unsure of which inlet zone corresponds to the cold inlet, you can probe the mesh display using the right mouse button or the probe toolbar button ( ) as described in a previous step. The information will be displayed in the ANSYS FLUENT console, and the zone you probed will be automatically selected from the Zone selection list in the Boundary Conditions task page.

(a)   Select Components from the Velocity Specification Method drop-down list.

  The Velocity Inlet dialog box will expand.

(b)   Enter 0.4  ${\rm m/s}$ for X-Velocity.

(c)   Retain the default value of 0  ${\rm m/s}$ for both Y-Velocity and Z-Velocity.

(d)   Select Intensity and Hydraulic Diameter from the Specification Method drop-down list in the Turbulence group box.

(e)   Enter 5 ${\rm\%}$ for Turbulent Intensity.

(f)   Enter 4 ${\rm inches}$ for Hydraulic Diameter.

  The hydraulic diameter $D_h$ is defined as:

where $A$ is the cross-sectional area and $P_w$ is the wetted perimeter.

(g)   Click the Thermal tab.

(h)   Enter 293.15  ${\rm K}$ for Temperature.

(i)   Click OK to close the Velocity Inlet dialog box.

2.   In a similar manner, set the boundary conditions at the hot inlet ( velocity-inlet-6), using the values in the following table:

Boundary Conditions velocity-inlet-6 Edit...

Velocity Specification Method	Components
X-Velocity	0  ${\rm m/s}$
Y-Velocity	1.2  ${\rm m/s}$
Z-Velocity	0  ${\rm m/s}$
Specification Method	Intensity & Hydraulic Diameter
Turbulent Intensity	5 ${\rm\%}$
Hydraulic Diameter	1  ${\rm inch}$
Temperature	313.15  ${\rm K}$

3.   Set the boundary conditions at the outlet ( pressure-outlet-7), as shown in the Pressure Outlet dialog box.

Boundary Conditions pressure-outlet-7 Edit...

Note:    ANSYS FLUENT will use the backflow conditions only if the fluid is flowing into the computational domain through the outlet. Since backflow might occur at some point during the solution procedure, you should set reasonable backflow conditions to prevent convergence from being adversely affected.

4.   For the wall of the pipe ( wall), retain the default value of 0  ${\rm W/m}^2$ for Heat Flux in the Thermal tab.

Boundary Conditions wall Edit...