# Why is a perfect heat engine Impossible?

Contents

## Why is it impossible to invent a perfect engine?

No matter how good of an engineer you are, you can’t invent a perfect engine. Why? It’s because of an energy crisis that pervades our universe. And it’s caused by entropy and the second law of thermodynamics.

## Can a heat engine be perfectly efficient?

We know from the second law of thermodynamics that a heat engine cannot be 100% efficient, since there must always be some heat transfer Qc to the environment, which is often called waste heat.

## Why 100 efficiency is impossible?

It cannot be constructed since it violates the second law of thermodynamics : Kelvin Planck Statement. If efficiency = 100%, then Temperature of the sink = 0 K which is again impossible to achieve. Thus, a Carnot engine with 100 % efficiency is not possible.

## Why do not possible to construct a perfect both heat engine and refrigerator?

The net heat removed from the hot reservoir is ΔQ, no net heat transfer occurs to or from the cold reservoir, and work W is done on some external body. Since W=ΔQ, the combination of a perfect refrigerator and a real heat engine is itself a perfect heat engine, thereby contradicting the Kelvin statement.

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## Is a perfect engine possible?

While Carnot engines are ideal engines, in reality, no engine achieves Carnot’s theoretical maximum efficiency, since dissipative processes, such as friction, play a role. Carnot cycles without heat loss may be possible at absolute zero, but this has never been seen in nature.

## What is the efficiency of Carnot engine?

The Carnot Efficiency is the theoretical maximum efficiency one can get when the heat engine is operating between two temperatures: The temperature at which the high temperature reservoir operates ( THot ). The temperature at which the low temperature reservoir operates ( TCold ).

## Why are heat exchangers not 100% efficient?

Efficiency is typically less than 100% because there are inefficiencies such as friction and heat loss that convert the energy into alternative forms.

## Can efficiency be more than 100%?

Due to the conservation of energy, P can never be greater than C, and so the efficiency r is never greater than 100% (and in fact must be even less at finite temperatures).

## Why are heat engines inefficient in general?

In real thermodynamic systems or in real heat engines, a part of the overall cycle inefficiency is due to the losses by the individual components. In real devices (such as turbines, pumps, and compressors), mechanical friction, heat losses, and losses in the combustion process cause further efficiency losses.

## Can a Carnot engine be 100% efficient?

In order to achieve 100% efficiency (η=1), Q2 must be equal to 0 which means that all the heat form the source is converted to work. The temperature of sink means a negative temperature on the absolute scale at which the temperature is greater than unity.

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## Can you design a heat engine of 100 efficiency?

The impossibility of converting heat energy completely into mechanical energy, limits the efficiency of heat engines. Since heat energy can never be transformed completely into mechanical energy, so the efficiency of a heat engine can never be 100 per cent.

## Is it possible to build a Carnot engine?

Carnots engine cannot be real because 100% efficiency cannot be obtained in real life. This is because, to achieve 100% efficiency in Carnot’s engine the temperature of the sink must be as least as possible.

## Does the refrigerator violate the second law?

Refrigerators appear to violate the Second Law of Thermodynamics, but the key reason they do not is because of the work needed as input to the system. They are essentially heat pumps, but work to cool a region instead of heat it.

## Where is the waste heat generally disposed of from a heat engine?

The heat absorbed by the engine comes from a place called hot reservoir, while the waste heat is dumped into the cold reservoir.

## Is it impossible to transfer energy by heat from cold to hot?

The second law of thermodynamics claims that it is impossible for heat to spontaneously flow from a cold body to a hot body, but it can move in that way if some form of work is done. This is how the refrigeration process works, and an example can be seen in Figure 1.