Step 9: S2S Definition, Solution and Postprocessing with Partial Enclosure

  As mentioned previously, when the S2S model is used, you also have the option to define a "partial enclosure"; i.e., you can disable the view factor calculation for walls with negligible emission/absorption, or walls that have uniform temperature. Even though the view factor will not be computed for these walls, they will still emit radiation at a fixed temperature called the "partial enclosure temperature". The main advantage of this is to speed up the view factor and the radiosity calculation.

In the steps that follow, you will specify the radiating wall ( w-low-x) as a boundary zone that is not participating in the S2S radiation model. Consequently, you will specify the partial enclosure temperature for the wall. The partial enclosure option may not yield accurate results in cases that have multiple wall boundaries that are not participating in S2S radiation and that each have different temperatures. This is because the a single partial enclosure temperature is applied to all of the non-participating walls.

1.   Read the case file saved previously for the S2S model ( rad_b_1.cas.gz).

File $\rightarrow$ Read $\rightarrow$ Case...

2.   Set the partial enclosure parameters for the S2S model.

Boundary Conditions w-low-x Edit...

(a)   Click the Radiation tab.

(b)   Disable Participates in S2S Radiation in the S2S Parameters group box.

(c)   Click OK to close the Wall dialog box.

3.   Compute the view factors for the S2S model.

Models Radiation Edit...

(a)   Enter 473 K for Temperature in the Partial Enclosure group box.

(b)   Click Compute/Write... for Methods in the View Factors group box to open the Select File dialog box and to compute the view factors.

  The view factor file will store the view factors for the radiating surfaces only. This may help you control the size of the view factor file as well as the memory required to store view factors in ANSYS FLUENT. Furthermore, the time required to compute the view factors will reduce as only the view factors for radiating surfaces will be calculated.

Note:   You should compute the view factors only after you have specified the boundaries that will participate in the radiation model using the Boundary Conditions dialog box. If you first compute the view factors and then make a change to the boundary conditions, ANSYS FLUENT will use the view factor file stored previously for calculating a solution, in which case, the changes that you made to the model will not be used for the calculation. Therefore, you should recompute the view factors and save the case file whenever you modify the number of objects that will participate in radiation.

i.   Enter rad_partial.s2s.gz as the file name for S2S File.

ii.   Click OK in the Select File dialog box.

(c)   Click OK to close the Radiation Model dialog box.

4.   Initialize the solution.

Solution Initialization

5.   Start the calculation by requesting 650 iterations.

Run Calculation

  The solution will converge in approximately 631 iterations.

6.   Save the case and data files ( rad_partial.cas.gz and rad_partial.dat.gz).

File $\rightarrow$ Write $\rightarrow$ Case & Data...

7.   Compute the radiation heat transfer rate.

Reports Fluxes Set Up...

(a)   Make sure that Radiation Heat Transfer Rate ia selected in the Options group box.

(b)   Select all boundary zones except default-interior from the Boundaries selection list.

(c)   Click Compute and close the Flux Reports dialog box.

8.   Compare the temperature profile for the side wall to the profile saved in tp_1.xy.

Plots XY Plot Set Up...

(a)   Select all of items in the File Data selection list and click Free Data.

(b)   Display the temperature profile and write it to a file named tp_partial.xy, in a manner similar to the instructions shown in Step 7: 11. (a)-(f).

(c)   Read and display the temperature profile saved in tp_1.xy, in a manner similar to the instructions shown in Step 8: 10. (f)-(g).

(d)   Close the Solution XY Plot dialog box.

Figure 5.19: Temperature Profile--With and Without Partial Enclosure (1 FPSC)