Card 6m - Minimum Allowable View Factor VFMIN

L

L is the code VFMIN (or 24)

VAL

VAL is a value. 0 ≤ VAL ≤ 1

Code example

 VFMIN .001          $ SETTING VAL FOR VIEW FACTORS OF ENCLOSURE 1
 VFS12 ENC1 ENC1                  
 VFMIN .0001         $ SETTING VAL FOR VIEW FACTORS OF ENCLOSURE 2
 VFS12 ENC2 ENC2
 

Notes

• This card sets a minimum value for unshadowed view factors, default = 1.0E-10.
• If the estimated value of a view factor is < VAL for both elements, that view factor is not calculated. If it is calculated, and is < VAL, it is not written on file VUFF.
• The value of VAL is in effect until a subsequent VFMIN Card is encountered.
• A VFMIN Card can considerably speed up view factor calculations for large models. However, care should be exercised in setting the value of VAL, since it can significantly affect the energy balance. A rule of thumb is that VAL < 1/10N is safe, where N is the number of elements in the model (or enclosure).
• The difference between the Card 2a RK parameter and the VFMIN Card is that VFMIN prevents the calculation of small view factors, thus reduces run–time of the VUFAC module, while the RK parameter eliminates small radiative couplings caused by small gray body view factors for Gebhardt's Method.
• Both the VFMIN and RK options should be used together to save CPU time, since small radiative couplings will still be created by the GRAYB module, even though there may not be any small view factors in the model.
• For the Card 9 PARAM OPPENHEIM option the RK parameter is not available, only VFMIN is effective.