4 ms·
This is a misunderstanding of Carnot cycle efficiency. The thing that makes the Carnot cycle special is that it is reversible. So in principle, you can get 100%
by jwmerrill 9y ago
This is a misunderstanding of Carnot cycle efficiency. The thing that makes the Carnot cycle special is that it is reversible. So in principle, you can get 100% of the mechanical energy that you put in back out again, by running the process in reverse.
The usual efficiency calculation for a Carnot cycle tells you what fraction of heat energy that's removed from the hot reservoir can be converted to mechanical work. This is always less than 100%.
However, when running the cycle in reverse as a heat pump, it is possible to transfer more than one Joule of energy from the cold reservoir to the hot reservoir per Joule of mechanical energy used. That's why the round trip efficiency from mechanical energy back to mechanical energy can be 100%.
I have no idea what the practical efficiency of this system can be. But it's wrong to immediately reject it on theoretical grounds.
- sitkack 9y agoThe Ouroboros Data Center.
- snovv_crash 9y agoIndeed. The Carnot Cycle has nothing to do with the efficiency, since it can be reversed in what is typically referred to as a "Coefficient of Performance", which is always bigger than 1 (assuming you aren't using straight resistive/friction heating). I seem to recall from Thermos lecturers that a CoP for consumer fridges is often in the 4 - 6 range, and it increases the smaller the difference in temperature between sink and source is, inversely to the Carnot efficiency. That said, due to heat capacity of pump components and conduction losses, I would be surprised if the total cycle efficiency was above 80%, putting this well below gravity and battery storage schemes. Maybe it is just incredibly cheap? Water does have a high heat capacity...