Due largely, I suspect, to Rich's cross posting, I'm getting responses off-list to my comments. I'll repost one of them here, because it might be worthwhile for others to see it.
On 02/08/2011 02:59 PM, Dan G wrote: >> "....there is no apparent reason for the output >> > temperature to hold steady at barely above boiling, as it did." > > Um, no live steam buffs here apparently. At sea level an open boiler system > releases heat at 100 c. Increase your heat source all you want, you will > burn your tubes but still only get 100 c. out. You must pressurize the > system to raise the temp. (pressure cookers to cook above 212 f.). > [sal responds:] Nuh, uh. You, also, are making the mistake of imagining this as a boiler with a fixed water supply, with a /submerged/ heating element, and with the steam emission rate determined by the power level. None of those assumptions are correct. In this case, the steam output rate is *fixed* and is determined by the positive displacement pump. It is not related to the power level. Let me say it again: *This is not an open boiler!* This is a tube, open at one end, with water being pumped in the other end, at a constant, /fixed/ rate, and sufficient heat being applied in the middle of the tube to (at least) boil all the water as it arrives. What, exactly, keeps the newly produced steam which is produced from absorbing *more* heat from the walls of the tube as it continues its way along the reactor? Nothing, of course. Furthermore, water vapor, like any gas, obeys PV = nRT, and if you boost the temperature of the steam while holding the pressure constant at 1 atm, you just boost its volume. Nothing magic there! To claim you can't have steam hotter than 100C unless you put it under more than 1 atm of pressure makes about as much sense as saying you can't have oxygen hotter than -183C unless you put it under more than 1 atm of pressure! (Seriously, think about that one -- the analogy is exact.) In an open boiler with a submerged heating element, the steam won't rise above 100 C, because its temperature is buffered by the liquid water with which it's in contact. In a pipeline, once the water has boiled away to steam, the steam is no longer in intimate contact with liquid water, but it's still in contact with the heating element, and there's nothing to keep it from getting hotter as it moves along the tube.
