Discussion
The rate at which heat is extracted, in kJ/s from the refrigerated space is
Answer: A
Heat is extracted at about 28.3 kJ/s.
In the ideal cycle the refrigerant enters the evaporator at the enthalpy of saturated liquid at 800 kPa (the throttle keeps enthalpy constant) and leaves as saturated vapour at 120 kPa:
\[ \begin{aligned} h_{1} &= h_{g,120} = 237\ \text{kJ/kg} \\ h_{4} &= h_{f,800} = 95.5\ \text{kJ/kg} \\ Q_{L} &= 0.2(237-95.5) = 28.3\ \text{kJ/s} \end{aligned} \]
Using hf at 120 kPa (22.5) instead of at 800 kPa gives 42.9 kJ/s, which ignores the throttling. 34.4 and 14.6 do not follow from the table.
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