seven_tech t1_j18u41q wrote on December 22, 2022 at 2:58 PM

Reply to comment by samskiter in Why do we use phase change refrigerants? by samskiter

An ideal Carnot cycle is Isentropic. The real world isn't ideal. Entropy is increased in the real world because of loss of energy through friction, intra-molecular force in gas and other similar processes.

And again, liquid is a much better transfer medium for heat than gas inherently.

samskiter OP t1_j193400 wrote on December 22, 2022 at 4:00 PM

Yea that seems to be the conclusion, but was wondering about the why. Like why we don't try and get as close to the carnot cycle as possible. The replies with numbers helped a lot with getting a sense / intuition for the scales and sizes that make the liquid so much better

seven_tech t1_j1anx4r wrote on December 22, 2022 at 10:13 PM

That's kind of like asking why don't we try and get to the theoretical efficiency of an internal combustion engine - what does it solve? Liquid to gas refrigeration systems are inherently more efficient, so it doesn't serve any real purpose to try. Same as we know we can't keep using petrol, so there's no longer a point to try in ICEs.

samskiter OP t1_j1cnzgp wrote on December 23, 2022 at 8:53 AM

It's more like saying why we use 4 Vs 2 stroke.

seven_tech t1_j1coweo wrote on December 23, 2022 at 9:05 AM

Mmm, kind of? 2 stroke has its place though. It's reliable, cheap to build and easy to maintain vs 4 stroke. Which makes it perfect for simple engines like lawn mowers and yard trimmers.

Gas-gas refrigeration doesn't really have any advantages over liquid-gas. So we don't really use it since perfecting the gas-liquid version. They used to use air refrigeration cycles. But not really anymore because it's so bulky due to the sheer amount of space/gas needed.