Chapter 5, Problem 5.54P

3.5 An ammonia refrigeration system operates between saturated suction temperature of -20°C, and saturated discharge temperature of +40°C. Com- pare the COP of the cycle using wet compression with that of the cycle using dry compression. Assume that the vapour leaving the compressor is saturated in the case of wet compression, and the vapour entering the compressor is saturated in the case of dry compression. The refrigerant leaves the condenser as saturated liquid.

4.46. An ideal Solvay refrigerator utilizing nitrogen as the working fluid operates between 0.101 and 2.02 MPa with the compression handled isothermally at 300 K. The maximum tem- perature in the cold space is 190 K. If the work obtained from the expansion process is used to reduce the work of compression, determine the net work per unit mass compressed, the refrigeration effect per unit mass compressed, and the figure of merit for the refrigeration system. To simplify the calculations, it may be assumed that the mass of gas present in the regenerator during the expansion process is negligible compared to the mass of gas in the expansion volume.

A refrigeration unit utilises ammonia as the refrigerant. The diagram for the circuit isshown in Figure Q3 below, with the following conditions: point (1) is a saturated liquidat –30 oC, points (3), (4) and (7) is a saturated liquid at 10 oC and point (5) is a saturatedvapour at –30 oC. The isentropic efficiency of the compressor and pump is 80% and itis assumed there are negligible heat losses to the surroundings. The liquid ammoniahas a specific volume of 0.0015 m3 kg-1. (a) Discuss which factors must be considered when selecting an appropriate refrigerant?(b) Calculate the coefficient of performance (COP) of the cycle.(c) If the effect of refrigeration is 10 kW, determine the required mass flow rate.