Study on the Liquid Refrigerant Defrosting System and the Defrosting Rule

The liquid refrigerant defrosting (LRD) is a defrosting method which leads the liquid refrigerant in the high-pressure reservoir to the frosting evaporator. The refrigeration process is continuous during the defrosting period, which increases the defrosting frequency. Compared with the traditional defrosting method, no large fin spacing should be left to reduce the defrosting frequency. The system can recover all the defrosting cooling capacity to improve the subcooling, so that the indoor air temperature fluctuations are avoided. In order to explore the effect and the rule of the LRD, the defrosting experiments were carried out in different frosting mass under the condition of the cold storage temperature of −20 °C. The defrosting time, temperature rise value, cooling capacity, and compressor power consumption value were calculated at the different frosting mass. Interpolation and applying the curve fitting equation helps to obtain remaining values. The relative humidity was calculated by the frosting mathematical model. Finally, the relationship between the coefficient of performance (COP) and the defrosting cycle (the sum of the defrosting time and the frosting time) was obtained. The experiments and theoretical research showed that the fluctuating value of cold storage temperature was about 5 °C and the defrosting time was about 30 min during the defrosting process. In the case of the relative humidity of 70%, 80%, 90%, the optimum defrosting cycle of the experiment was 16.4, 10.9, 7.5 h and the frosting mass was 2.66, 2.90, 3.22 kg, and the maximum COP was 1.51, 1.48, 1.45.