Problem:

Refrigeration systems manufacture 40 kg/hr of ice at 0^oC from water at 25^oC. Determine the refrigeration effect per hour & TR. If this consumes 1 kW of energy to manufacture the ice, determine the COP. Take latent heat of solidification of water at 0^oC as 335 kJ/kg and specific heat of water 4.19 kJ/kg ^oC.

Solution:

Heat elimination rate to form 40 kg of ice at 0^oC from water at 25^oC

Q_c = sensible cooling from 25^oC to 0^oC + latent heat of solidification of water

= 40 kg/hr * (25 - 0) ^oC * 4.19 kJ/kg. ^oC + 40 kg/hr * 335 kJ/kg

= 4190 kJ/hr + 13400 kJ/hr

= 17590 kJ/hr

Refrigeration effect (Q_C) = 17590 kJ/hr

As we know that 1 TR = 210 kJ/min = 12600 kJ/hr

Thus, TR equal to 17590 kJ/hr = 17590 kJ/hr /1.396 =12600 kJ/hr