> From: "Joshua Cude" <joshua.c...@gmail.com> > Sent: Monday, May 27, 2013 2:41:34 PM
> And just in case you're wondering how e effects the calculated power > > P = a . e . (T1^4 - T0^4) -- T1 actual, T0 ambient > > a e Tc Tk P > area 18 1.00E-10 0.8 564.1 837.1 38.84 <=== lower "e" OVER-estimates the power > area 19 1.00E-10 1 496.6 769.6 34.52 > area 20 1.00E-10 0.95 511.7 784.7 35.49 > You're right. I did that calculation too. But the reason they're not > equal is because they use an effective exponent not equal to 4 when > they calculate temperature. It's not clear what that effective > exponent would be if the emissivity were set to 0.2, and so we don't > know what the effect would be there. And in particular, we don't > know what the effect would be if the emissivity depended on > wavelength. The literature warns about poor accuracy in such cases. But it's NOT metal : it's metal-ceramic-paint. AND the "blank" test was in the same temperature range as the "live" test. They checked it with a) DOTS of known emissivity and b) A thermocouple -- giving results in reasonable agreement with the calorimeter.
