The Study Of Thermal And Humid Environment Characteristics Of Controlled Atmosphere (CA) Storage

The storage capacity and arrangement of fruits and vegetables affect the thermal environment in controlled atmosphere(CA) store. During the long-term storage, frosting of the chiller, moisture loss of fruits and vegetables and humidification of the humidifier affect the humid environment and its distribution. The environment of the cold store under different running conditions of the equipment is different. This paper studied the changing process of thermal and humid environment according to the operating conditions at the different stage.In this paper, a 50 t CA storage for apples in Xi’an of is numerically studied. k-?(SST) model is selected and user-defined function(UDF) program of respiration of fruits and vegetables is written to get the real respiratory heat and gas components. The detailed numerical calculation were generalized as follows:1) In order to verify the reliability of numerical calculations and UDF, the simulated results of temperature during the cooling process and O2 volume fraction during the oxygen reducing process was compared with the measured values, showing good agreement with each other.2) To research the effect of storage capacity on thermal environment, the cooling time as well as the distribution and the quality of the temperature field after cooling were mainly considered. The cooling time increases with the increase of storage capacity. The cooling time was more than 90 hours when the storage capacity exceeded 58 t, the temperature of the apples could not decrease to meet the requirement in less than 3 days. During the cooling period, the temperature at center point increased first and then decreased. The temperature of the point increased when the storage capacity is larger, which can increase to 279.3 K. Meanwhile, the uniformity coefficient of temperature decreased and lower the quality of the environment.3) The storage capacity of goods affect significantly the reduction time of O2 concentration. According to the numerical calculation, the reduction time of O2 concentration is getting much shorter with the increase of storage capacity.4) Five different arrangements of apples are comparatively studied in this paper. The cooling time and the thermal and humid environment at the end of cooling are simulated and compared. The conclusion shown that there must be some suitable distance in cargo area. The best arrangement should be with the distance from goods to goods to be 0.5 m, and 0.3 m between goods and wall.5) The cooler frosting and the humidification of the humidifier were considered to be the main influence factor on the humid environment in the CA storage on the basis of numerical calculation. The relative humidity dropped with the increase of frost on the cooler. The relative humidity of the airflow area decrease faster than that of the cargo area. When the humidifier is working, the relative humidity changed greatly at first and then slowly. Similarly, the relative humidity of the airflow area changed quickly than the cargo area.The developed 3-D physical and mathematical models of air flow, heat and mass transfer inside the CA storage can be applied to get the changing thermal and humid environment. The research would provide a theoretical guide to the management of the real CA storage.