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But chip-cooling devices will take a while to arrive. It now takes 120 volts to get the polymer to change its atomic arrangement, and that figure would need to be much lower if the material is to be used in laptops. "Ideally, you want it to work at voltages common within the realm of a notebook, in the tens of volts or less," Mongia says. The researchers will also need to engineer a working device containing the thin films.
Electrocaloric materials could make fridges greener. Current household fridges use a vapor-compression cycle, in which a refrigerant is converted back and forth between liquid and vapor to absorb heat from the insulated compartment. The need for mechanical compression lowers the fridge's efficiency. "Vapor-cooled fridges are 30 to 40 percent efficient," Mathur says. But because electrocaloric materials have no moving parts, they could lead to cooling devices that are more energy efficient than current fridges. What's more, current hydrofluorocarbon refrigerants contribute to global warming.
Refrigerators that use electrocaloric materials would have an advantage over the magnetic cooling systems that some companies and research groups are developing. Electric fields large enough to produce substantial temperature changes in electrocaloric materials are much easier and cheaper to produce than the magnetic fields used in experimental refrigeration systems, which require large superconducting magnets or expensive permanent magnets. However, refrigerators need temperature spans of 40 °C, which is a tall order for electrocaloric materials right now, Mathur says. "The main sticking point in terms of the technology is that we have thin films, and you can't cool very much with a thin film."
Zhang and his colleagues are now trying to design better electrocaloric polymers. They plan to study polymers made from liquid crystals, which are used in flat-panel displays. Liquid crystals contain rod-shaped molecules that will align with an electric field and revert to their original arrangement when the field is removed. Zhang says that this property could be exploited to make materials that absorb and release large amounts of heat in response to electric fields.
By using an electric charge to put molecules in motion, a new device can make a computer's fans more efficient.
Computer fans could get some relief from charged particles that create a cooling breeze.
A novel way to cool microprocessors.
This article is not very specific so let me lay out how you could use this. I would recommend people that have not read http://en.wikipedia.org/wiki/Heat_pipe
to read it. A heat pipe can be used as a thermo check valve. “See thermo diode”
Some ascii art
Heat sync
IIIIIIIIIIIIIIIIII < heat pipe
Fancy new device
IIIIIIIIIIIIIIIIII < heat pipe
Cold object
The heat pipe could be the micro channel kind that are very thin, all it requires is a phase change that allows the heat to travel in only one direction.
I see no reason that you could not stack several such devices, but I suspect it would rapidly loose efficiency like the Peltier Effect coolers do.
That's an interesting variation on heat pipes that I haven't seen before. In this incarnation, it is dependent on gravity to draw water from the condenser, and so is dependent on orientation, and also looks difficult to make efficiently in a thin package, so it's a bit of an unlikely choice for laptops, but it could certainly have other uses.
I wonder if something other than gravity could be used to "polarize" the device...perhaps a fully solid state heat diode could be created. It might even be a relative of this variable-heat-capacity plastic film...
All of the applications mentioned in these threads and in the article are probably of great significance, but what I want is a hat for tennis that will cool the head. Passive and active heat retaining or generating clothing is already on the marketplace, but cooling clothing is a rarity. Overheating for athletes compromises performance. There may be some way to adapt this to help.
Consider the power requirements and the mass/bulk of the heat exchangers. It might cool your head, but if it means carrying a backpack of batteries and aluminum fins on your head...
You'd probably be better of working on improvements to those gel headbands...evaporative cooling seems to be the way to go for this application.
Why can't the heat being pulled out of the fridge or freezer be used to heat water for washing or drinking/cooking etc. , for instance so that less energy has to be used to boil water for drinking ? Plus , dusting the heat exchanger regularly is a good way to ensure it works as efficiently as possible .
I agree that the efficiency of these plastics will be substantially lower than advanced heat pump cycles. By association, that makes this a niche application. So not very exciting in terms of energy impact. But there may be some interesting applications where efficiency isn't paramount but portability and other aspects are strongly valued. Think micro-electronics. I'm not sure about microprocessors though; they are a substantial energy requirement of society, so efficiency is important.
Many of these MIT articles contain too much marketing talk. Universities should not subscribe to this; it is downgrading MIT's intellectual property. Just like Nocera's absurd claims, it's just bad journalism on MIT's side.
Hope to see more objective, fuller disclosed articles on this site.
There is a mistake there: "current hydrofluorocarbon refrigerants contribute to global warming". You should know that CFCs or haloalkanes or whatever you want to call them do not contribute to the global warming effect, they destroy the ozone layer. That is equally dangerous, but a different process though!
So, you have this plastic which you apply voltage to to get it's chemical state to flip, which cools it off by 12C. Now the object you are cooling gives it enough energy to raise it 12C again.
What do you do then? If you switch it back, it will end up 12C hotter than it's initial state.
Do you have a belt of this material cycling between the cooled object and the heat sink/radiator?
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
This document is part of the “How-To Guide for Most Common Measurements” centralized resource portal. This tutorial provides a detailed guide for measurement and device considerations to take temperature measurements using thermocouples. Get an introduction to thermocouples, which are inexpensive sensing devices widely used with PC-based data acquisition systems. Also review some specific thermocouple examples and learn how thermocouples work and ways to integrate them into a data acquisition measurement system.
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GGMarquez
1 Comment
Cool polymer
Normal COP (efficiency) of small refrigerators is over 100% (depends on the temperature level). Even if we only talk about the efficiency of the compressor it is higher than 30-40% indicated. Besides, HCFCs are on the way out from the small friges, typically replaced by R600a. I think this film looks promising, but it is yet nowhere near to be attractive for home friges.
Reply
clark.gilbert@newmont.com
1 Comment
Re: Cool polymer
COP being the inverse of efficiency can exceed 100%. How would this compare in efficiency to Peltier Effect cooling?
Reply
slipperyweasel
2 Comments
Re: Cool polymer
Actually the COP can be greater than 1 as it is Q/W. Efficiency cannot be greater than one as it is W/Q, the reciprocal of COP.
Reply
stevengt
4 Comments
Re: Cool polymer
Yep. Can't confirm the formula, but this is why a so-called "heat pump" can deliver more energy (in the form of heating or cooling) than it "burns" in terms of electrical energy. It uses the electrical energy to *move* existing heat into (or out of) the building, rather than directly converting electrical energy into heat (as with 'emergency' backup heating coils in heat pumps).
But, would it be possible to 'cascade' these thin-film devices (like cells in a battery) to achieve the necessary differential? That is, the first "layer" would chill 12 degrees, passing the heat to a second layer which would in turn lower it another 12 degrees, then to a third and a fourth, achieving a combined differential of more than the needed 40 degrees. Seems this would all be within the operating temperature range already achieved, though the efficiency may drop significantly with the multiple layers.
Reply
cjameshuff2
16 Comments
Re: Cool polymer
Temperature's temperature, the film has no way to know if it's at a given temperature due to the action of other layers of film...so cascading should work just fine. As long as the film on the cold/hot sides stay in their respective operating temperature ranges, anyway.
"In a cooling device, a voltage would be applied to the material, which would then be brought in contact with whatever it's intended to cool. The material would heat up, passing its energy to a heat sink or releasing it into the atmosphere. Reducing the electric field would bring the polymer back to a low temperature so that it could be reused."
The explanation's a bit unclear...but apparently the film is to be brought into contact with a heat sink, exposed to an electrostatic field to raise its temperature and dump out the heat stored in it, then brought in contact with the object being cooled and the electrostatic field removed, cooling the film and allowing it to absorb heat. Voltage-controlled heat capacity, essentially.
I am uncertain how this makes a cooling system with no moving parts however, the description specifically uses the phrase "brought in contact with". However, the distance to move can be very tiny, and the motion could be done electrostatically (as in electrostatic speakers) or piezoelectrically, the motion being just enough to preferentially transfer the heat in the desired direction. And perhaps there's changes in thermal conductivity as well which make it possible to eliminate the need for motion...
Operating at 120 V is not an issue for laptops. Laptop cold-cathode backlights operate at hundreds or even thousands of volts. As a result, there's a wide range of compact, high efficiency, high voltage inverter designs that could be used for powering a heat pump.
Reply
bcollegec
1 Comment
Re: Cool polymer
I think you two are a little off on your logic. You're forgetting about the law of diminishing returns more or less. If what you say was true, then they'd be able to bring any substance to almost absolute zero with the film... Unfortunately... if for example the temp of the air is 40 degrees celsius and the film could lower itself from 40 to 28, multiple layers would only help the air approach 28 degrees. It would get closer and closer to 28 degrees, but never actually go below it UNLESS the film could go below it. Multiple layers WOULD be GREAT for larger quantities or more efficiency though
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