移动式冷库性能及其冷却均匀性分析

    Analysis of the performance and cooling uniformity of mobile cold storage

    • 摘要: 针对果蔬冷链运输过程中采摘后的“最先一公里”的保鲜问题,该研究开发了一种移动式冷库。该设备用于田间果蔬预冷以及冷藏,以消除果蔬采摘后的田间热和呼吸热。对该设备冷库库板的导热热阻、机组制冷系数以及冷库内部的冷却均匀性进行了性能试验研究,并采用温度异质性系数和温度变异系数用以评价冷库内部的冷却均匀性。结果表明,冷库板的导热热阻为3.98 m2·°C/W,制冷一体机的制冷系数为2.07,具有较高的导热热阻以及制冷系数,有利于设备的节能运行;设备运行过程中冷库门侧左上角测点处具有较低的温度异质性系数为0.08 %,制冷机组侧右上角测点处具有较高的温度异质性系数为0.48 %,冷库整体的温度变异系数为0.034%,不论是温度异质性系数还是温度变异系数均低于0.5 %,可以认为该冷库具有较高的冷却均匀性,将有利于降低果蔬预冷过程的损腐率。

       

      Abstract: Fruits and vegetables still have vital signs after harvest. Their field heat and respiration of biological entities can greatly dominate the quality of fresh products for a better shelf life. This study aims to keep the fruit and vegetable fresh in the first kilometer after picking during cold chain transportation. An integrated equipment system of mobile cold storage and refrigeration was developed for the precooling and storage of fruits and vegetables in fields, in order to eliminate the field heat and respiratory heat after picking. The performance of the equipment was analyzed from three aspects: the thermal resistance of cold storage panels, the coefficient of performance of the integrated refrigeration, and the cooling uniformity inside the cold storage. Among them, the cooling uniformity was also evaluated using temperature heterogeneity and variation coefficients. Two experiments were carried out to verify the performance and cooling uniformity of mobile cold storage. The heat balance method was used to measure the thermal resistance. Notably, the integrated refrigeration machine was also shut down during the experiment. The temperature difference between the inside and outside of the cold storage was maintained by the external heater and axial fan. Temperature measurement points were arranged 100 mm away from the geometric center of the inside and outside of the cold storage. At the same time, there were eight measuring points 100 mm from three sides of the cold storage top angle inside the cold storage, one of which was arranged in the geometric center of the cold storage. As such, the temperature field distribution was measured to calculate the performance and cooling uniformity of the mobile cold storage, according to the flow and heat transfer characteristics. The results showed that the high thermal resistance of the cold storage panels is 3.98 m2·℃/W and the coefficient of performance of the integrated refrigeration machine is 2.07, which were conducive to the energy-saving operation of the equipment. There was a small overall fluctuation (about 0.1%) of the temperature heterogeneity coefficient at each measurement point in the process of equipment operation. The largest overall fluctuation was lower than 1%, only when the integrated refrigeration machine was shut down and defrosted. The temperature heterogeneity coefficient was lower at the upper left corner of the cold storage door (0.08 %), and higher at the upper right corner of the refrigeration unit (0.48 %). The temperature coefficient of variation was 0.034% in the integrated refrigeration machine. Both the temperature heterogeneity and variation coefficients were lower than 0.5 %. Therefore, cold storage with high cooling uniformity can be beneficial to reduce the decay rate of fruits and vegetables in the process of pre-cooling.

       

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