Chapter 5, Problem 5.67P

3.24 You want to cool air from 150°C to 60°C but you cannot afford a custom-built heat exchanger. You find a used cross-flow exchanger (both fluids unmixed) in storage. It was previously used to cool 136 kg/min of NH3 vapor from 200°C to 100°C using 320 kg/min of water at 7°C; U was previously 480 W/m²K. How much air can you cool with this exchanger, using the same water supply, if U is approximately unchanged? (Actually, you would have to modify U using the methods of Chapters 6 and 7 once you had the new air flow rate, but that is beyond our present scope.)

Q1. A vapour compression refrigeration uses R-12 as a refrigerant and the liquid evaporates in the evaporator at - 15°C. The temperature of this refrigerant at the delivery from the compressor is 15°C when the vapour is condensed at 10°C. Find the C.O.P. if (i) there is no under cooling (ii) the liquid is cooled by 5°C before expansion by throttling. Take specific heat at constant pressure for the superheated vapour as 0.64KJ/kg k. and that for liquid as 0.94KJ/kg k the other properties of refrigerant are as follow: a) Temperature b) 0°С с) Enthalpy(KЈK)) d) Entropy(KJ/kg k) e) liquid _j) 22.3 0) 45.4 f) Vapour k) 180.88 g) liquid 1) 0.0904 9) 0.1750 h) Vapour m) 0.7051 i) -15 n) 10 p) 191.76 r) 0.6921

Only solve if u are 100% sure about Sol