can anyone solve this problem??? The vapor-compression refrigeration system show

Question

can anyone solve this problem???

The vapor-compression refrigeration system shown in Figure 1 below uses R134gas its working substance. The pressures upstream and downstream of the compressor are 28 psia and psia, respectively. Saturated liquid exits the condenser, and there is a 20 degree F sub-cooling before the fluid is throttled, for the conditions given calculate: The COP for the cycle with sub-cooling The COP of the cycle without sub-cooling The percent increase in refrigerating effect between part (a) and (b) The percent increase in required work between parts (a) and (b)-

Explanation / Answer

ANSWER THIS WILL HELP YOU The sub-cooling or under-cooling in the saturated liquid line increases the refrigeration effect or cooling effect, thus the COP of VCR system increases. Superheating (referring to superheating of the refrigerant vapor leaving evaporator) and subcooling (referring to subcooling of refrigerant liquid leaving the condenser) are apparently two significant processes in practical vapor-compression refrigeration systems and are applied to provide better efficiency (COP) and to avoid some technical problems, as will be explained below. Superheating During the evaporation process the refrigerant is completely vaporized partway through the evaporator. As the cool refrigerant vapor continues through the evaporator, additional heat is absorbed to superheat the vapor. Under some conditions such pressure losses caused by friction increase the amount of superheat. If the superheating takes place in the evaporator, the enthalpy of the refrigerant is raised, extracting additional heat and increasing the refrigeration effect of the evaporator. If it is provided in the compressor suction piping, no useful cooling occurs. In some refrigeration systems, liquid-vapor heat exchangers can be employed to superheat the saturated refrigerant vapor from the evaporator with the refrigerant liquid coming from the condenser (Figure 3.32). As can be seen from Figure 3.32, the heat exchanger can provide high system COP. Refrigerant superheating can also be obtained in the compressor. In this case, the saturated refrigerant vapor enters the compressor and is superheated by increasing the pressure, leading to the temperature increase. Superheating obtained from the compression process does not improve the cycle efficiency, but results in larger condensing equipment and large compressor discharge piping. The increase in the refrigeration effect obtained by superheating in the evaporator is usually offset by a decrease in the refrigeration effect in the compressor. Because the volumetric flow rate of a compressor is constant, the mass flow rate and the refrigeration effect are reduced by decreases in the refrigerant density caused by the superheating. In practice, it is well known that there is a loss in the refrigerating capacity of 1% for every 2.5

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