The study of vapor-compression refrigeration cycles in refrigerators via energy and exergy analysis

A typical 250 l cooler type refrigerator is analyzed based on experimental data by employing the first and second laws of thermodynamics at steady state in order to quantify the location of loses on component-level and to determine the efficiency potential of each component. The refrigerator is equipped with data acquisition to measure temperature, pressure, flow rate, and power consumption at major locations of the refrigeration cycle, and operated at standard test conditions. Until the refrigerator cycle reaches the steady state, all data were measured and recorded at certain period. Based on the measured data, invaluable properties of the refrigerant such as enthalpy, and entropy are determined, and energy and exergy rates for components modeling them as steady flow systems are calculated to quantify the sites and amounts of energy and exergy loses. The results are tabulated in tables, and energy and exergy flow diagrams are drawn to elucidate where loses and inefficiencies are occurring. The analysis indicates that the second law efficiency is 4,3% which is very low compared with other refrigerators, although the first law efficiency is within a normal range (In fact, it is very close to the value of 1,3 given in the compressor specification). The reasons for such a low second law efficiency are due to large exergy destructions in the compressor, after the condenser, evaporator, suction line heat exchanger, and dryer-capillary tube. The major sources of the exergy destructions are the heat transfer across finite temperature differences between the refrigerant and the mediums, as well as flow friction and subsystem heat transfers. One of the most significant results drawn from the study is that a compressor should be taken as a key component for a higher efficiency refrigerator.