3 ms·
Carnot limit has nothing to do with heating efficiency, only with converting heat into mechanical work
by pi-e-sigma 3y ago
Carnot limit has nothing to do with heating efficiency, only with converting heat into mechanical work
- kragen 3y agoincorrect, the carnot cycle is reversible (like everything in physics up to cp reversal, except for entropy increase), so it also has to do with converting mechanical work into heat (differences) specifically, in this case, if you convert a hypothetical 2770° flame into mechanical work in a hypothetical heat engine capable of withstanding it, you can use that mechanical work to drive a heat pump to pump ten times as much heat into the house to heat it up to 30°. or more, if the temperature outside is higher than 0°
- pi-e-sigma 3y agovery correct, because we are talking about using high temperature flame as somehow wasteful when used for heating. How does converting heat into mechanical work even enter equation?
- kragen 3y agosorry, i was still editing as you replied
- pi-e-sigma 3y agoEven in this revised scenario it's not clear if you were able to get ahead. Because you are converting heat to mechanical work and back to heat in the heat pump so you are subject to Carnot limit _twice_
- kragen 3y agoyes, but the second time it works backwards: for each joule of mechanical work you put in, you pump 10.1 joules of heat. this is called the 'coefficient of performance' of a heat pump and it is almost always more than 1, even with the losses present in any real system. values of 2 or 3 are typical, though some mass-produced systems reach 6. sometimes this is quoted as an 'efficiency' of 200% or 300% or 600% which is of course impossible, but it's as if you had 200% efficiency. that's why using heat pumps saves energy