Question

Ice is formed at 0°C from water at 20°C. The temperature of the brine is – 8°C. Find out the kg of ice formed per kWh. Assume that the refrigeration cycle used is perfect reversed Carnot cycle. Take latent heat of ice as 335 kJ/kg.

Answer 1

Latent heat of ice = 335 kJ/kg 

T₁ = 20 + 273 = 293 K 

T₂ = – 8 + 273 = 265 K

Heat to be extracted per kg of water (to form ice at 0°C i.e., 273 K), R_n 

= 1 × c_pw × (293 – 273) + latent heat of ice 

= 1 × 4.18 × 20 + 335 = 418.6 kJ/kg 

1 kWh = 1 × 3600 = 3600 kJ

Hence ice formed per kWh = 81.35 kg.