Engineering Thermodynamics: An Introduction by M. Kassim D. Khudhur H. Hussain L. Habeeb

Author:M. Kassim, D. Khudhur, H. Hussain, L. Habeeb [Paul Turner]
Language: eng
Format: epub, mobi
Publisher: David Pallai
Published: 2022-05-15T00:00:00+00:00

FIGURE 6.7 P-V diagram of the reversed Carnot cycle.

6.5.2 Carnot Cycle for Heat Pump and Refrigerator

A heat pump or refrigerator working on a reversed Carnot cycle is called as refrigerator or a Carnot heat pump.

The coefficient of performance (COP) of any refrigerator or heat pump is calculated as follows:

The COP of the reversible refrigerators or heat pumps is calculated as follows:

Similar to the heat engine, one can conclude:

(6.18)

6.5.3 Carnot Cycle for Heat Engine

All heat engines working on the principles of Carnot cycle are called the Carnot heat engines. The thermal effectiveness of any heat engine (irreversible or reversible) is calculated as follows:

(6.19)

where QH is the heat transferred to the engine from the reservoir at a high temperature TH, and QL is the heat rejected to the reservoir at low temperature TL.

For the reversible heat engines, the ratio of heat transfer with reservoir is equal to the ratio of the temperatures of the two reservoirs.

Therefore, efficiency of a Carnot engine, or some reversible heat engine, will be as follows:

(6.20)

This is the maximum efficiency of heat engine working between thermal reservoirs TH and TL as shown in Figure 6.8.

All irreversible (real) heat engines working in the range of two temperature limits (TH and TL) have lesser efficiency.

The actual thermal efficiencies of the heat engines working between the same ranges of temperatures (Figure 6.9) are as follows:

(6.21)

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