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 perfectreversedCarnot cycle. Take latent heat of ice as 335 kJ/kg

Answer 1

The mass of ice is 81.35 Kg

Explanation:

Latent heat of ice = 335 kJ / kg

T1 = 20 + 273 = 293 K

T2 = – 8 + 273 = 265 K

C.O.P. = T 2 /  T1 - T 2  = 265  /  293 - 265 = − 9.46

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

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

= 1 × 4.18 × 20 + 335 = 418.6 kJ/kg

1 kWh = 1 × 3600 = 3600 kJ

Also, C.O.P. = R n / W

n = Refrigerating effect in kJ/kg  / Work done in kJ

9.46 = m (ice) × 418.6  / 3600

m (ice)  = 9.46 x 3600 / 418.6 = 81.35 Kg