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  4. In a refrigerator, the low temperature coil of evaporator is at -23℃ and the compressed gas in the condenser has a temperature of 77℃ . The amount of electrical energy spent in freezing 1 kg of water at 0℃ is

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Q. In a refrigerator, the low temperature coil of evaporator is at $-23℃$ and the compressed gas in the condenser has a temperature of $77℃$ . The amount of electrical energy spent in freezing 1 kg of water at $0℃ is$

NTA AbhyasNTA Abhyas 2020Thermodynamics

Solution:

COP $=\frac{T_{2}}{T_{1} - T_{2}}=\frac{273 - 23}{\left(273 + 77\right) - \left(273 - 23\right)}=\frac{250}{100}=2.5$
As COP $=\frac{Q_{2}}{W}$
$\therefore \, 2.5=\frac{1000 \times 80 \times 4.2}{W}$
or $W=\frac{1000 \times 80 \times 4.2}{2.5}=134400 \, J$