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Kelvin's statement says:

It is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects.

What actually happens when we cool down the body lower than the surrounding that it cant perform the work?

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  • $\begingroup$ Kelvin is saying that heat will not flow from low temperature objects to high temperature objects. $\endgroup$ Commented Dec 15, 2020 at 16:25
  • $\begingroup$ But there is presence of high temperature source as well. It could also extract heat from that high temperature source and perform functioning whatever the temperature of surrounding is.But it doesnt happen. The temperature of working substance has to be greater than surroundings temperature. please clarify. $\endgroup$ Commented Dec 15, 2020 at 16:32
  • $\begingroup$ Heat doesn't flow from cold to hot, no matter what device you use. Even in a refrigerator, the evaporating refrigerant is colder than the inside of the refrigerator, so heat still flows from hot to cold. $\endgroup$ Commented Dec 15, 2020 at 16:36

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I think you have misunderstood what Kelvin's statement means.

Suppose we have some object at the same temperature as its surroundings. We can cool it to below the surrounds by lots of processes that require work to be put in. The refrigerator in your kitchen does exactly this.

However there is no process that can cool the object to below the temperature of its surroundings and get work out. This is what Kelvin's statement means.

This should be obvious since if it were possible to get work out from some process that cooled an object to below the temperature of its surrounding then we could use this to create energy. We would cool the object and get work out, then let it warm up again and get more work out. Repeat the cycle and we get energy from nothing.

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What actually happens when we cool down the body lower than the surrounding that it cant perform the work?

What happens? You DO some work instead of the matter in question doing useful work for you. In everyday life, your fridge cools its internals below the surrounding temperature and you get the electricity bill.

In addition, the whole process heats something else.

The essence of the Kelvin's statement is that you cannot convert heat into work with the only effect of cooling something down (this would be a perpetual motion machine of some king).

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What actually happens when we cool down the body lower than the surrounding

You decrease the overall entropy of the system, by ordering it into a cold part and a warm part.

that it cant perform the work?

Because decreasing entropy takes work, not the other way around.

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