Reversed Heat Engines

Reversed Heat Engines

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Reversible heat engines work by transferring energy in the opposite direction to regular heat engines. Instead of transferring energy from a hot region to a colder one, they transfer energy from a colder reservoir to a hotter one by adding work. This process follows the second law of thermodynamics, which states that heat naturally flows from hot to cold regions. Heat engines convert thermal energy into mechanical work, but some of the energy is lost to the surroundings. Reverse heat engines, on the other hand, use a cyclical process to transfer energy between hot and cold reservoirs. They require an electric compressor to pump heat out of the system. Check out the table below to see the differences between heat and reverse heat engines.

If you want to learn more about reversible heat engines, take a look at Figure 1 below. It shows the flow of energy as it moves from a lower temperature region to a higher one by adding work. Keep in mind that this process cannot happen naturally, which is why an external source like an electric compressor is needed to help move the heat out of the system.

Reversible heat engine energy flow diagram
Reversible heat engine energy flow diagram

Reverse heat engines discharge energy into the surroundings, which is a combination of work and heat transfer. Heat and work are both measured in Joules, but they have different characteristics in their motion. Heat is the kinetic energy of disordered movement of atoms, while work is the kinetic energy of ordered motion of atoms in the same direction. Reverse heat engines have two main applications: refrigerators and heat pumps. Refrigerators cool down a space by removing heat, and work is done on the system using a motor. Heat pumps are designed to remove heat from a cold region and transfer it to a hotter one. A fluid is circulated through a closed system, which involves an adiabatic expansion and an isobaric expansion. A compressor adds work to the system, and heat is transferred to the room through isobaric compression. A p-v diagram can be used to describe this process, and the coefficient of performance (COPref) measures the amount of heat transfer from the cold region compared to the work input to the system.

P-V diagram of a refrigerator

Reverse heat engines transfer energy in the opposite direction to regular heat engines by following the second law of thermodynamics. Heat pumps and refrigerators are the two main applications of reversible heat engines. Heat pumps are used to warm up a room, and their COPhp is calculated by dividing the amount of heat transferred into a space by the work input. Refrigerators cool down a space, and their COPref is calculated as the ratio of heat removed per unit work input. The efficiency of a reverse heat engine is calculated by dividing the work done by the heat transferred. The COP formula can be used to find the heat transferred or the work done, while the efficiency formula can be used to calculate the efficiency. The COPref of a refrigerator and the COPhp of a heat pump are related by an equation that can be derived using the equation of work and the heat pump coefficient formula. The higher the COP, the higher the efficiency, and heat pumps show greater performance when the temperature difference is small.

Reversed Heat Engines

What is a reversible heat engine?

It is an engine that does work by transferring energy from a lower temperature body to a higher temperature body.

What is the difference between a heat engine and a reversed heat engine?

In a heat engine, heat is transferred from hot reservoir to a colder one, whereas in a reverse heat engine, heat is transferred from a colder to a hotter region.

Is a reversible heat engine possible?

Yes, reversible heat engines are possible by providing additional external work.

Define a reversible heat engine.

A reversible heat engine is an engine that transfer heat from a lower temperature object to a higher temperature object by adding external work, usually using electric motors.

What is the efficiency of a reverse heat engine?

The efficiency of a reverse heat engine is found by the dividing the work by the heat transfer  as shown below. η= W/ QH

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