Are there any naturally occurring heat pumps?
post by FactorialCode
This is a question post.
By that I mean are there any natural phenomena that use a low entropy energy source to move heat against a temperature gradient. I know that there are a lot of things that can be interpreted as heat engines, like hurricanes, but I wanted to know if the opposite also happens in nature.
answer by Dagon
) · GW
Warm-blooded creatures (mammals and some birds) move heat around their bodies fairly effectively.
Deep-water heat sources set up convection currents that counter the "natural" gradient.
↑ comment by kithpendragon ·
2020-04-13T16:18:17.509Z · LW(p) · GW(p)
Warm blooded creatures use tricks like evaporative cooling and flow control to move heat around. Some birds, for example, have the veins and arteries in their legs tangled up in such a way that the blood headed toward their feet can give heat back to the cooled blood that's headed back toward the heart. This prevents a lot of heat loss, but doesn't actually move heat from low- to high-density regions within the body. Most of the heat involved comes from chemical processes within the cells releasing energy that, ultimately, came from sunlight.
Convection currents distribute heat throughout water by completely normal thermodynamic means: hotter (less dense) water becomes buoyant and rises, displacing cooler (denser) water down toward the heat source. Having moved away from the heat source, the warm water eventually releases the excess heat to the cooler environment and the cycle repeats. Again, there is no heat moving the "wrong" way in those systems.
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comment by Decius ·
2020-04-13T09:02:15.776Z · LW(p) · GW(p)
Are you excluding things like forest fires? Replies from: kithpendragon
↑ comment by kithpendragon ·
2020-04-13T10:37:38.934Z · LW(p) · GW(p)
I don't think of fire as moving heat around so much as converting chemical energy (derived from electromagnetic) into thermal.
Replies from: Decius
↑ comment by Decius ·
2020-04-14T04:02:04.320Z · LW(p) · GW(p)
It creates a local area that is higher temperature than it would be without the photosynthesis->chemical energy->fire chain of events. Since energy is conserved there must also be a local area that is lower temperature than it would otherwise be, and I can't think of a way it would be cooling something hotter than the fire.
It's a weak example, but the direction of search I have is "Find a process that results in higher local temperatures than would exist without that process". The other competitor is planet and star formation, which (oversimplified) took a gas cloud very slightly warmer than the cosmic background radiation and concentrated much of it into hotter stars and planets. My engineering thermodynamics education breaks down in astronomical space, because it doesn't actually enumerate all the assumptions it makes, including "acceleration due to gravity is constant over time".
comment by kithpendragon ·
2020-04-13T10:44:20.911Z · LW(p) · GW(p)
Off the top of my head: I know some chemicals (like sodium acetate, found in reusable hand warmers) change form when heated and can be easily coerced to change back, releasing the stored heat in the process. I'd be surprised to learn that there aren't any natural processes that take advantage of behavior like that, but I don't think I actually know of any.
comment by stoat ·
2020-04-13T19:42:14.143Z · LW(p) · GW(p)
I wonder if I'm understanding this correctly: is something like sweating an example of refrigeration, since it keeps the low temperature thing from heating up? And heat pumps are different, they keep a hot thing from cooling down, but otherwise the underlying thermodynamic processes are similar?
If I've got that straight, is any evaporative cooling an example of refrigeration, but the question here is specifically wondering about heat pumps not refrigerators?Replies from: Decius, kpreid
↑ comment by Decius ·
2020-04-14T12:11:43.030Z · LW(p) · GW(p)
Sweating is an example of evaporative cooling, but the fancy part of refrigeration and heat pumps is the compressor, which does work on the coolant that results in the coolant moving heat from a colder part of the loop to a warmer part of the loop.
Sweating takes heat out of the skin, but in nature the water vapor then has to move all the way to somewhere cooler than body temperature before it will condense back into rain; if you follow the water cycle it's moving heat from a hotter location to a cooler location.
I think the spirit of the original question was "is there a natural system that moves heat from a cool part of the world to a warmer part of the world?"
↑ comment by kpreid ·
2020-04-13T20:58:11.918Z · LW(p) · GW(p)
For what it's worth, https://en.wikipedia.org/wiki/Evaporative_cooler takes the perspective (in one paragraph) that “Vapor-compression refrigeration uses evaporative cooling, but the evaporated vapor is within a sealed system, and is then compressed ready to evaporate again, using energy to do so.” So, in this perspective, evaporative cooling is a part of the system and forced recirculation (requiring the energy source mentioned in the question) is another.
heat pumps not refrigerators
Note that what is colloquially called a heat pump is the same fundamental thing as a refrigerator — equipment is referred to as a “heat pump” when it is used for heating rather than, or in addition to, cooling, but the processes and principles are the same (with the addition of a “reversing valve” so that the direction of operation may be changed, when both heating and cooling are wanted).