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Nano-engineered thermoelectrics enable scalable, compressor-free cooling

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Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#21

Post by s_tec »

Thermoelectric cooling is pretty inefficient, because the materials need to balance competing requirements:

- Good thermal insulator - Good electrical conductor - Good semiconductor

This is because the hot & cold sides are sandwiched closely together as a PN junction, so once you move heat from one side to the other, it just leaks right back. Mechanical cooling doesn't have this problem, because the hot & cold sides are separated by thin bits of tubing. This makes the thermal leakage a "minor annoyance" in a mechanical system as opposed to "literally the whole problem we're trying to solve" as it is with thermoelectrics.

One work-around is to stack lots & lots of thermoelectric coolers on top of each other. That reduces the temperature difference at each individual PN junction, which in turn lowers the leakage. That's what this team is doing, but using layers that are only a few nanometers thick, so they can fit dozens or hundreds of junctions in a single package.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#22

Post by leptons »

vlovich123 wrote: post #20
fnordpiglet wrote: post #7

Thermoelectric cooling needs as much research as possible. Mechanical cooling is extraordinarily space consuming. CHESS has the potential over the next 10 years to largely replace vapor compression in most systems other than the most extreme gradients or scales. They are small enough to incorporate into most devices and would allow smaller devices more thermal load. In some ways I think efficient TEC like CHESS could…

Nah. Heat pumps are ~10-100x more efficient than thermoelectric. Thermoelectric is just inefficient mechanism and is inherently difficult to scale up as the more electricity gets generated so does more heat which inhibits the temperature gradient you’re trying to utilize. There’s a reason water cooling is preferred instead of peltier to ferry heat away from electronic. Magnetocaloric is super interesting though as an…

>Heat pumps are ~10-100x more efficient than thermoelectric.

Peltier junctions are a type of heat pump.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#23

Post by bob1029 »

fnordpiglet wrote: post #7

Thermoelectric cooling needs as much research as possible. Mechanical cooling is extraordinarily space consuming. CHESS has the potential over the next 10 years to largely replace vapor compression in most systems other than the most extreme gradients or scales. They are small enough to incorporate into most devices and would allow smaller devices more thermal load. In some ways I think efficient TEC like CHESS could…

> Mechanical cooling is extraordinarily space consuming.

You'd wind up taking up even more space with a TEC solution at these efficiencies. To replace a 5-ton condensing unit you'd have to reject on the order of 50-100kW of heat.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#24

Post by vlovich123 »

leptons wrote: post #22
vlovich123 wrote: post #20

Earlier quoted context omitted.

Nah. Heat pumps are ~10-100x more efficient than thermoelectric. Thermoelectric is just inefficient mechanism and is inherently difficult to scale up as the more electricity gets generated so does more heat which inhibits the temperature gradient you’re trying to utilize. There’s a reason water cooling is preferred instead of peltier to ferry heat away from electronic. Magnetocaloric is super interesting though as an…

>Heat pumps are ~10-100x more efficient than thermoelectric. Peltier junctions are a type of heat pump.

Mechanical heat pumps are 10x-100x more effective than peltier heat pumps.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#25

Post by ajb »

s_tec wrote: post #21

Thermoelectric cooling is pretty inefficient, because the materials need to balance competing requirements: - Good thermal insulator - Good electrical conductor - Good semiconductor This is because the hot & cold sides are sandwiched closely together as a PN junction, so once you move heat from one side to the other, it just leaks right back. Mechanical cooling doesn't have this problem, because the hot & cold sides…

Twenty years ago there was a company trying to commercialise thermoelectric cooling based on a vacuum gap: https://web.archive.org/web/20031213235132/http://www.coolch...

They claimed 55% Carnot efficiency based on a 30-100 angstrom gap maintained by piezoelectric controllers, and a method to construct large electrodes with matched surfaces so that the gap could be maintained over a large area. It all sounded plausible but never went anywhere as far as I know.

Incidentally that means all their patents will have expired...

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#26

Post by scotty79 »

adrian_b wrote: post #17
speed_spread wrote: post #10

Earlier quoted context omitted.

> can't move the heat very far. Heat pipes (as in CPU heatsinks) can passively move the heat up to a feet away. Far enough to allow effective insulation between cold and hot side. From there you can move the heat further away with a fan.

Heat pipes only reduce the thermal resistance between 2 points. They cannot cool something below ambient temperature. Thermoelectric coolers do not compete with heat pipes. They are useful only when you want to obtain a temperature lower than the ambient temperature. Otherwise, heat pipes or liquid flow cooling are the right solutions.

You could have heat pipe filled with liquid that evaporates at 5 degrees. This way it would draw heat from ambient level temperature and lead it to peltier device that would cool it below 5 deg and liquefy it back again. This way you could have peltier in the middle of your thick insulation layer with heat pipes drawing the heat into it from the cooled space and drawing the heat from the other side of it outside (using traditional heat pipes this time).

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#28

Post by nandomrumber »

vlovich123 wrote: post #20
fnordpiglet wrote: post #7

Thermoelectric cooling needs as much research as possible. Mechanical cooling is extraordinarily space consuming. CHESS has the potential over the next 10 years to largely replace vapor compression in most systems other than the most extreme gradients or scales. They are small enough to incorporate into most devices and would allow smaller devices more thermal load. In some ways I think efficient TEC like CHESS could…

Nah. Heat pumps are ~10-100x more efficient than thermoelectric. Thermoelectric is just inefficient mechanism and is inherently difficult to scale up as the more electricity gets generated so does more heat which inhibits the temperature gradient you’re trying to utilize. There’s a reason water cooling is preferred instead of peltier to ferry heat away from electronic. Magnetocaloric is super interesting though as an…

Further to that, have a look at the refrigeration units on chest type portable fridges. They’re really not very big, compressor smaller than a roast chicken, small low speed fan similar to an auxiliary cooling fan in a PC, a controller board, and a few meters of metal tubing.

They typically consume around the 50 to 80 watts while the compressor and fan are running, and generate two to four times that in cooling capacity.

Surely people have adapted these in to PC cooling units?

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#29

Post by nandomrumber »

mkw5053 wrote: post #19

I need this for my compact compost freezer [1] [1] https://www.envirofreezely.com/

I’ll watch your video later when I get home. Mostly leaving a comment so I can find it easier later.

Freezing food waste prior to composting it results in much faster breakdown in the compost.

Re: Nano-engineered thermoelectrics enable scalable, compressor-free cooling

#30

Post by nandomrumber »

markhahn wrote: post #18
adrian_b wrote: post #16

Earlier quoted context omitted.

Also in the article, it is implied that there is no chance to replace mechanical compressors for great thermal powers, but for small thermal powers, from a few watt to a few hundred watt, thermoelectric devices may become preferable, due to small size, simplicity and reliability

just noting that household fridge/freezers are in that power range...

Yeah but, household freezers are typically capable of freezing many tens of kilograms of material down to -18 to -24 degrees C / 0 to -10 F

Peltier coolers aren’t anywhere near this.

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