Hacker News Reader

Comment by Chabsff | Hacker News Reader

You can only cool something by making something else warmer by a larger amount. The heat has to go somewhere, and moving that heat in any non-passive way will invariably produce yet more heat in the process.

View on HN

I think some people are interpreting that as a joke. I'm not talking about a net gain of energy or any crazy perpetual motion machine. Think of something like a "heat brake". Differential heat energy can be converted to mechanical work. Some of that can be used to cool the system elsewhere, creating a negative feedback loop. Another way to think of such a system is like the "reluctance" of an inductor.

With present thermoelectric effects, using a Seebeck junction to generate current for a fan is hopelessly ineffective. But is that necessarily the case for all designs which could help to hold a system under a critical temperature when heat spikes.

do you mean something like a solar chimney, where heat is used to draw air through the rest of the building?

https://en.wikipedia.org/wiki/Solar_chimney

That's an example of a similar system, but probably impractical for use in an electronics context. I have in my imagination a fantasy "smart" material that in the limit can transfer 0.5 * k^m joules of heat per square meter per second from one side to the other (where m is somewhere between 1 and 2). Such a material would always feel slightly warmer on one side and cooler on the other, and this effect would actually increase in the presence of ambient heat, hence it could act as a thermal "brake" or active heat pipe/diode. I beleieve such a device is "allowable" within the laws of physics.

The goal is to quickly and efficiently conduct heat from the DRAM (A) to the outside world (B). You could generate a little power from the temperature difference between A and B, but that would greatly reduce the effectiveness of the heat transfer. Perhaps that generated power could cool something else, but you'd waste power (and generate heat) in the process. Net loss.

> You can only cool something by making something else warmer by a larger amount.

Why isn't it also true that you can only make something warmer, by cooling something else by a larger amount?

The movement of electricity generates waste heat, why isn't that process reversible? Making the heat disappear into a cold wire, rather than just dissipating into the atmosphere? (not suggesting it's would be easy or even practical).

2nd law of thermodynamics - entropy is always increasing. Heat transfer is never 100% efficient, you always lose something in transmission. This is also why it's not possible to create a perpetual-motion machine.

https://en.wikipedia.org/wiki/Second_law_of_thermodynamics

Peltier coolers [1] do exist for specialist applications but they are not at all effective. You can even buy them on Amazon. If the goal is to iron out a spike to stop your semiconductor from going into thermal runaway (instead of generating net energy as is the knee-jerk of some unimaginative down-voters here) then it's a possible saviour.

[1] https://www.britannica.com/science/Seebeck-effect

[2] https://www.amazon.com/Peltier-Cooler/s?k=Peltier+Cooler

Reply on news.ycombinator.com