Effect of Throttling Variation on the Performance of Vapour Compression Refrigeration System

Abstract

In this paper, the effect of throttling variation on the performance of vapour compression refrigeration system using R134a refrigerant as working fluid was investigated and reported. The investigation was carried out using a refrigeration test rig with capillary line as throttling device which was split into three capillary lines of the same length under a room temperature condition of 29 – 32°C. The test rig was equipped with four sigma manifold gauges which were installed at the inlet and exit of the condensing and evaporating units to take the pressure and temperature readings of the working fluid. Experimental trials were conducted by taking the pressure-temperature readings when one-, two- and all the three capillary lines were engaged for the throttling process. The enthalpy condition of the refrigerant at the inlet and exit of the condenser and evaporator were obtained from a standard COOLPACK saturation table. The performance of the refrigeration system was analysed based on the experimental data. Results showed that the temperature difference between the inlet and exit of the evaporating unit was found to increase from 8.66°C to 24.65°C, refrigerating effect increases from 141.2 kJ/kg to 144.6 kJ/kg while work done by compressor decreases from 24.8 kJ/kg to 21.6 kJ/kg as the number of capillary lines employed increases from one to three. The coefficient of performance of the system was found to increase from 5.69±0.04 to 6.71±0.04 which was 17.9% and 7.5% higher than the COP of the system if only one- and two capillary lines were respectively employed for the throttling process. The system behaviour has been attributed to earlier development of the two-phase mixture from the saturated liquid as the number of capillary line increases, thus improving the system performance.