Question

16 Explain the working of a heat engine and a refrigrator with
a labelled block diagram giving efficiency and Coefficient.
of perfi​

Answer 1

Explanation:

In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy—and chemical energy—to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat source generates thermal energy that brings the working substance to the high temperature state. The working substance generates work in the working body of the engine while transferring heat to the colder sink until it reaches a low temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid. During this process, some heat is normally lost to the surroundings and is not converted to work. Also, some energy is unusable because of friction and drag.

A refrigerator does not cool items by lowering their original temperatures; instead, an evaporating gas called a refrigerant draws heat away, leaving the surrounding area much colder. Refrigerators and air conditioners both work on the principle of cooling through evaporation.

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Answer 2

Answer:

Heat engine is a thermodynamics device which converts heat energy into mechanical energy (work).

Working of Cornot's engine:

Step 1: The working substance (ideal gas) is enclosed in a non-conducting wall and conducting bottom of a cyclinder fitted with air tight non conducting piston. This is placed on the source having in infinite thermal capacity at a steady temperature. The top surface is conducting and the rest non conducting. As a result, the gas expands isothermally. The work done by the system,

W1=μRT1log.V2V1(Curve A B)

Step 2: The working substance is now placed on a non conducting platform, as a result of which no heat exchange takes place between the system and the surroundings. The system expands adiabatically at the expense of its internal energy. The gas cools. The work done by the system,

W2μRγ−1(T1−T2)(Curve B C)

Step 3: The working substance is now placed on the sink maintained at a steady low temperature T2K. The system undergoes isothermal compression at this temperature. The pressure of gas increases and volume decreases without any change in internal energy and specific heat of gas remain at infinity.

W3=μRT2log(V4v3)(Curve C A)

Step 4 : The working substance is placed on a non-conducting platform. Under thermal isolation, the system undergoes change in its internal energy and its specific heat remains at zero. Adiable compression results in increase in the pressure and temperature at the expense of work being done on the system. The system is allowed to reach its initial state. This completes one cycle of operation. The area bounded by the curves gives the amount of heat converted into work.

W4=−μRγ−1(T1−T2)(Curve D A).

i.e., Net work done =W=W1+W2+W3+W4.

Work done =μR(T−T2)loge(V2V1).