[Since87]

Originally posted by ]JR[
I dont, but why dont we all have tec's in our fridges and freezers @ home if they can do more work (i.e the heat pumped through the device) than the power input to do the work? Since they are better than phase change wrt moving parts/maintanance?

The reason we don't use TEC's in our homes is because they are less efficient than phase change for the tasks you mention. I didn't say that the first simulation I posted showed a system that was of any real use to anybody.

What do you mean by "work"? The physics definition of work involves moving a mass. There is no net movement of mass involved in the operation of a TEC.

Originally posted by ]JR[

Also thought experiment:
I take the coldsides of a large number of tecs and place them, for arguments sake into the sea, then i power them up, they then remove heat from the sea , the heat i get from the sea has more energy than i need to run the tec*. Correct and with me so far?

Yes, the energy contained in the heat removed from the sea, is in the form of material at a slightly higher temperature than the temperature of the sea.

Originally posted by ]JR[

So I now boil water with my heat removed from the sea (and the hotside of the tec), generating electricity, which is more than enough to power the tec* and have electricity left over to power my computer.

WHOA!!!

Boil water? Look at that simulation again. Th (the hotside temperature) is 23C. Even if you pull a vacuum I'm not sure you could get a phase change turbine system to run at 23C using water. But suppose you find another liquid to boil - so what? Can you design a system that can extract more than 1% of the available energy? If you've got a means for everyone living near a body of water to generate significant amounts of energy whenever there is a differential between the air and water temperature, you need to be getting in touch with a patent attorney.

Here's a link. It's not a particularly good link, but it was the first I found with a statement such as...

Quote:
"High efficiency air conditioning systems may require as little as 0.33 BTUs of energy to remove 1 BTU of heat."

Air conditioners dissipate heat by taking in outside air and putting out hotter air. By your reasoning, the energy contained in the temperature differential between masses of air, can be extracted and used to power the airconditioner and more. Why don't airconditioner manufacturers do this?

Originally posted by ]JR[

Hopefully that illustrates why you cannot get more work out of a system than the input work/energy/power (all one and the same) And also it illustrates why we have phase change rather than tecs in our fridges since phase change is ~75% efficent whereas tecs are less.
]JR[

There is not more energy coming out of the system than is going into it. The energy coming out of the TEC is exactly equal to the energy going into the TEC. Some of that energy is coming in as electricity, and some of it is coming in as heat from the heatsource. As far as "work" is concerned, I don't know what "work" you are talking about.

"Energy" is not the same thing as "Power". Power is a rate of energy dissipation/usage/whatever.

The reason phase change is used more commonly than TEC's is that phase change is usually more practical and efficient for jobs people want to do. Nobody is likely to want to go to the expense of using a TEC as a means of 'efficiently' cooling a 25 Watt heatsource to 0.2 °C below ambient. The fact that no one wants to do it, doesn't mean it can't be done though.