Design And Experiment Of Controlled Atmosphere Vaporizer By Liquid Nitrogen Injection Equipped On Transportation Of Fruits And Vegetables

Air conditioning and fresh-keeping transportation is one of the more advanced method for keeping fruits and vegetables. It has the advantages of high efficiency, environmental protection, and low cost. By controlling the gas components of the environmental preservation, the breath of fruits and vegetables is suppressed, the preservation period of fruit and vegetable is prolonged. In order to improve the efficiency of air conditioning, to prevent freezing damage from fruits and vegetables, a new type liquid nitrogen filling type vaporizer of air conditioning and fresh-keeping transportation is designed, and it has been tested. The main research contents and results of this article are as follows:(1) The air conditioning and fresh-keeping technology of the domestic and foreign is analyzed through the literature review. The research status of heat ex-changer in low temperature is summarized at present. The performance of heat transfer and frosting of finned vaporizer has been analyzed in emphasis. The research results provide basic theory for optimal design of the vaporizer.(2) In order to improve the air conditioning effect of liquid nitrogen injection type fresh-keeping transportation equipment, a liquid nitrogen filling type vaporizer is designed and a liquid nitrogen vaporization test platform is established. By changing the vaporizer fin spacing and the velocity of facing wind through the process of the liquid nitrogen injection test, we get and analysis the result of the outlet temperature of a vaporizer, the wall surface temperature and the amount of frost under the condition of different fin spacing and velocity of facing wind. The test results show that: The bigger the facing wind velocity is,the better the effect of heat transfer is,the higher the temperature of outlet is and the smaller the frost thickness is; the influence of the facing wind velocity on the wall temperature and the outlet temperature of the vaporizer is higher than that of the fin spacing; when the vaporizer facing wind velocity of the vaporizer is 0m/s. The larger the fin spacing, the higher the outlet temperature and the wall temperature, the better the heat transfer effect; when the vaporizer facing wind velocity is 0.8m/s, the smaller the fin spacing, the slower the frosting velocity, the higher the outlet temperature and wall temperature and the better heat transfer effect.(3) The oxygen reduction characteristics is analyzed insides fresh-keeping transportation. The changing of oxygen reduction rate and clapboard temperature insides transportation are analyzed in different conditions. The results showed as follows. Under the condition of wind speed of air returning way is 6m/s, the initial temperature is 5?and 80% relative humidity, The larger the fin spacing, the higher the temperature of vaporizer outlet and clapboard. The lower oxygen reduction rate insides fresh-keeping transportation. Under the condition of fin spacing is 4mm, the initial temperature is 5?and 80% relative humidity, The larger the speed of air returning way,the higher the temperature of vaporizer outlet and clapboard. The lower oxygen reduction rate insides fresh-keeping transportation. Under the condition of fin spacing is 4mm, the speed of air returning way is 6m/s and 80% relative humidity, The larger the initial temperature, the higher the temperature of vaporizer outlet and clapboard. The changing of oxygen reduction rate insides fresh-keeping transportation is small.(4) In order to grasp the effect of controlled atmosphere by liquid nitrogen injection on the homogeneity of flow fields in the transportation container, a liquid nitrogen vaporization test platform is established, the homogeneity of temperature fields and relative humidity inside the transportation container is studied by changing the vaporize fin spacing and the velocity of the air return way and the ambient temperature. The results showed that the fin spacing has a certain influence on the homogeneity of the temperature field and the relative humidity field in the transportation container. The homogeneity is relatively good when fin spacing is 7mm and relatively poor when fin spacing is 4mm; The larger the wind speed of air returning way, the better the homogeneity of temperature field and the worse the homogeneity of relative humidity field; The higher the ambient temperature, the better the homogeneity of temperature field and relative humidity field.Through finished the theory modeling of vaporizer, analyzed and studied of the performance of heat transfer and frosting, analyzed the the oxygen reduction rate and clapboard temperature and homogeneity of flow field besides transportation container, we complete the full design of vaporizer. The research results provide reference for further development of the fresh keeping equipment with controlled atmosphere.