A refrigerating system operates on a reversed carnot cycle. The higher temperature of the refrigerant in the system is 35°C and the lower temperature is -15°C. The capacity is to be 12 tonnes. The COP of the system is _______.

Question

Question

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JKSSB JE Mechanical 02 Nov 2021 Shift 1 Official Paper

Answer 1

Concept:

F1 Ashiq 21.9.20 Pallavi D20

Coefficient of performance of a refrigerator is given by:

\( {COP} = \frac{{Refrigeration~Effect}}{{Work~Input}} = \frac{{{Q_2}}}W\)

For reversible refrigerating machine:

\(COP=\frac{{{T_2}}}{{{T_1} - {T_2}}}\)

where Q1 = Heat rejected to the surrounding, Q2 = Heat absorbed from storage space

W = Work input = Q1 – Q2

Calculation:

Given:

T1 = 35°C = 308 K, T2 = -15°C = 258 K, Q2 = 12 tonnes = \(12\times3.5=42\) kW

The coefficient of performance of a reversible refrigerator is:

\(COP=\frac{{{T_2}}}{{{T_1} - {T_2}}}\)

\(COP = \frac{{258}}{{308 - 258}} = 5.16\)