Design and no-load performance test of GU-PCM2 temperature controlled phase change storage refrigerator

© 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved. The existing phase change material (PCM) devices of PCM refrigerated truck are mostly arranged on the top of the carriage, which has the problems of high gravity center and uncontrollable temperature and so on. In view of the above problems, a new type refrigerated truck was designed in this paper, which integrated phase change thermal storage unit, refrigeration system, heat-insulated carriage, air supply system and so on. The cold storage device was set independently in the front of the truck and was insulated. PCM mass required for phase change thermal storage unit was 360 kg (the phase transition temperature is -30℃ and the latent heat of phase change is 175.3 kJ/kg), which used cheap electricity at night to store energy, when working, the temperature in carriage could be adjusted between -25-10℃. The simulation and tests of 2 working modes were carried out with the setting temperature of 0 and -18℃ in a refrigerated prototype. A computational fluid dynamics (CFD) simulation model of PCM refrigerated truck was built and the temperature field in carriage was simulated, the root mean square error and maximum absolute error between simulations and measurements of 2 working modes were 0.7 and 0.8℃, 1.1 and 1.2℃ respectively, the simulated temperature calculated by the simulation model agreed well with the measured temperature, and the measured temperature near the air outlet in the carriage was slightly lower than the simulation temperature, while the measured temperature near the rear section was slightly higher than the simulation temperature, this was due to the fact that the simulation data were generally in an ideal state, but the cold leak was unavoidable at the return air outlet of the actual refrigerated truck and the heat leak (air leak) at the door. The test results showed that the new type of PCM refrigerated truck proposed in this paper could effectively control the temperature more than 10 h on the basis of sufficient cold storage. The average temperature fluctuated between 1.1-2.9℃ and -14.8--16.9℃ and the fluctuation ranges were 1.8 and 2.1℃ under the 2 working modes. The lowest temperature in the carriage was located at the front of the carriage and close to both sides of the air outlet, the high temperature area was located at the top of the middle of the carriage and near the air inlet. The coefficient of temperature non-uniformity was less than 1.0 when the setting temperature in carriage was 0℃ and was less than 0.4 when the setting temperature in carriage was -18℃. In terms of cooling time, it took 60 minutes when the carriage was set to 0℃ and 90 minutes when the carriage was set to -18℃. The tested results showed that the average temperature fluctuation of the new type temperature controlled PCM refrigerated truck was 48.7% lower than that of the traditional PCM refrigeration truck, the coefficient of temperature non-uniformity was 50% lower, and the center of gravity was 25.9% lower than that of the overhead traditional PCM refrigeration truck. In addition, the temperature stability of the new type PCM refrigerated truck was better than that of the similar mechanical refrigerated truck because it didn't need to defrost the evaporator during long-term operation. The new type PCM refrigerated truck can effectively reduce the transportation energy consumption and cost while guaranteeing the quality and safety of goods, and the research provided the basis for the optimization and application of the PCM refrigerated truck.

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