Josh questions: "I'm talking about the December test, when a different paint was used. I don't think we know anything about the emissivity of that paint, nor its dependence on wavelength."
You could just as easily do a 30 second search and FIND THE ANSWER! Emissivity of various materials: http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html Black Body Matt 1.00 Black lacquer on iron 0.875 Black Silicone Paint 0.93 Black Epoxy Paint 0.89 Black Enamel Paint 0.80 ALL of these black paints are within the range: 0.80 - 0.93 >From this document: http://www.scigiene.com/pdfs/428_InfraredThermometerEmissivitytablesrev.pdf (the figure on the far right is the emissivity) Paints Blue, Cu2O3 75 (24) 0.94 Black, CuO 75 (24) 0.96 Green, Cu2O3 75 (24) 0.92 Red, Fe2O3 75 (24) 0.91 White, Al2O3 75 (24) 0.94 White, Y2O3 75 (24) 0.9 White, ZnO 75 (24) 0.95 White, MgCO3 75 (24) 0.91 White, ZrO2 75 (24) 0.95 White, ThO2 75 (24) 0.9 White, MgO 75 (24) 0.91 White, PbCO3 75 (24) 0.93 Yellow, PbO 75 (24) 0.9 Yellow, PbCrO4 75 (24) 0.93 It should be obvious that most paints, REGARDLESS OF COLOR, have an emissivity >0.9. In addition, the value for the black paint used on the March reactor was ALSO in this range when emissivity 'dots' and a thermocouple were used as checks. If someone wanted to go back to the December reactor and substitute a value for emissivity, a value within this range is REASONABLE; using or suggesting something *other* than this would require justification. With the internet being so convenient, let's check for the emissivity for the underlying ceramic: ". having a *silicon nitride* ceramic outer shell, 33 cm in length, and 10 cm in diameter. " Emissivity between .88 to .98. See the chart a few postings from the top at this website: http://cr4.globalspec.com/thread/22307/Emissivity-Of-Silicon-Nitride-Si3N4 "A second cylinder made of a different ceramic material (corundum)." The above-linked table also lists: Silicon Carbide (carborundum) 0.83 - 0.96 But they specifically say, 'corundum', which is a crystalline form of aluminum oxide (Al2O3). This is a common geological mineral, and I have to wonder if they really meant carborundum (SiC)? -Mark Iverson From: Joshua Cude [mailto:joshua.c...@gmail.com] Sent: Monday, May 27, 2013 3:02 PM To: vortex-l@eskimo.com Subject: Re: [Vo]:Ekstrom critique of Levi et al. On Mon, May 27, 2013 at 4:58 PM, Alan Fletcher <a...@well.com> wrote: > 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. I'm talking about the December test, when a different paint was used. I don't think we know anything about the emissivity of that paint, nor it's dependence on wavelength. In the March test, the power estimate was better, though far from good, but the input was dodgier.
