In reply to Jones Beene's message of Tue, 19 Apr 2011 21:14:06 -0700: Hi, [snip] >Robin. > >My initial reaction is that the assumptions could be way off.
They probably are off to some extent, but I don't think they are way off. > >The delta-T of 500K is too large, This is based on an internal operating temperature of 600 ºC, and an external temperature of 100 ºC. > and the wall thickness of 2 mm is thin for >this application. Perhaps, but using http://www.engineersedge.com/calculators/pipe_bust_calc.htm and http://en.wikipedia.org/wiki/Ultimate_tensile_strength#Ductile_materials I calculated a pipe bursting pressure of 455 Bar (well in excess of the 20-25 Bar specified). However this doesn't take into account weakening of the metal at elevated temperatures, so it could still be a little too thin. This is at least partially compensated for by the fact that I excluded the ends from the calculation. (BTW from http://cr4.globalspec.com/thread/5058 I get a yield strength at 1500 ºF (815 ºC) of 18000 psi. If I use that instead, then I get a bursting pressure of 69 Bar, which is still a factor of 3 higher than that actually used.) >There could be other problems too. :) > >For 25 bar pressure, how are you going not to get by with 2 mm walls - more >like 6. If the temp gradient is like more like 300 - which would be water at >350 K and interior at 650K, and the wall is 6mm - this might be more >accurate. The water temperature is at most boiling point, or 100 ºC, however the internal operating temperature is about 500-600 ºC, so the difference is still 400-500 K. > >Next, the actual conductance is some fraction of maximum in practice, due to >surface oxidation on one or both sides. Not sure where to go for that >information. I don't think it would make much difference, because the thickness of any oxide layer is on the order of microns (not to mention that it was probably included anyway when the measurements for the thermal conductivity tables were initially made). > >This is where an expert opinion comes in handy. All in all, don't you think >it conceivable that this reactor runs at an order of magnitude less maximum >heat transfer, and the average could even be a fraction of that? > >Jones It is operating at a fraction of maximum. Even 130 kW is a fraction of 204 kW. However I have only guessed at the length of the E-cat cylinder (20 cm seemed reasonable to me, however increasing it to 60 cm while keeping the volume equal, would increase the power to 354 kW). It could be longer or shorter. BTW, the real problem may be the thermal transfer properties of the Ni itself, not so much the SS. If it's not bonded to the inner surface of the steel, then we are possibly looking at a much higher overall thermal resistance. The purpose of my calculations was to determine whether or not we could prove that the information we have been given is patently false. I have to come to the conclusion that what has been said is not necessarily ruled out by the measurements taken. In short I am inclined to take it at face value, at least for the time being. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
