Mark172
Aerospace
- Aug 26, 2008
- 43
Hi All,
When I load materials from the built-in FEMAP database "mat_eng_in-lbf-psi-degF-BTU.esp" for a thermal analysis, the conductivity and specific heat values don't make sense to me. I must be missing conversion units somewhere but for the life of me can't figure it out. I am using lbf-in-s-F units.
Example from the database:
Aluminum 6061 Annealed Wrought
Expansion Coeff, a = 1.3E-5
Conductivity, k = .0024074
Specific Heat, Cp = 88.872
The CTE units are obvious, that's ppm/F which is consistent with my unit system. From the Nastran user's guide, the conductivity should be lbf/s-F, but when I convert for aluminum at ~200 W/m-k, I get 200 w/m-K * .1249 (lbf/s-F)/(W/m-k) = 24.98 lbf/s-F which is off by what looks like a factor of 10000.
Similarly for specific heat: according to the nastran user's guide the units should be in^2/s^2-F. Using wolfram and verified with other sources, 1 J/kg-K = 861.1 in2/s2-F. So for aluminum at ~900 J/kg-K the thermal conductivity should be 774,990 in2/s2-F, off by a huge factor.
The strange values in the FEMAP database make me doubt that I'm doing these conversions correctly, I can't imagine their database's units are inconsistent. Thanks for your help.
When I load materials from the built-in FEMAP database "mat_eng_in-lbf-psi-degF-BTU.esp" for a thermal analysis, the conductivity and specific heat values don't make sense to me. I must be missing conversion units somewhere but for the life of me can't figure it out. I am using lbf-in-s-F units.
Example from the database:
Aluminum 6061 Annealed Wrought
Expansion Coeff, a = 1.3E-5
Conductivity, k = .0024074
Specific Heat, Cp = 88.872
The CTE units are obvious, that's ppm/F which is consistent with my unit system. From the Nastran user's guide, the conductivity should be lbf/s-F, but when I convert for aluminum at ~200 W/m-k, I get 200 w/m-K * .1249 (lbf/s-F)/(W/m-k) = 24.98 lbf/s-F which is off by what looks like a factor of 10000.
Similarly for specific heat: according to the nastran user's guide the units should be in^2/s^2-F. Using wolfram and verified with other sources, 1 J/kg-K = 861.1 in2/s2-F. So for aluminum at ~900 J/kg-K the thermal conductivity should be 774,990 in2/s2-F, off by a huge factor.
The strange values in the FEMAP database make me doubt that I'm doing these conversions correctly, I can't imagine their database's units are inconsistent. Thanks for your help.
