Abstract:
Abstract: At present, cold chain in China is developing rapidly, especially in the cold chain market of agricultural products, it has huge market potential. But the cold chain transportation still faces serious constrains for its development. The shortage of cold chain capacity and frequent discontinuity in the process of transportation deteriorate the quality of agricultural products. Thermal storage cold chain transportation equipment currently used includes refrigerated transportation with cold storage technology and adiabatic thermal insulation technology from which thermal storage insulation boxes are mainly used. Thermal storage insulation box is composed of heat preservation box and thermal storage plate. Thermal storage insulation box has no refrigeration function, the temperature is controlled by putting thermal storage plates of different temperature in the box, and the temperature could be maintained for a long time. The temperature of fresh-keeping and cold chain transportation are requested in the range of 2 - 8 ℃, the thermal storage material (sodium sulfate salt hydrate system) is wrapped in polyethylene thermal storage plate. It is used in polypropylene (EPP) foaming thermal storage boxes and vacuum insulation plate (VIP) boxes, and constitutes the thermal storage cold chain transportation equipment. Good Supply Practice (GSP) was used in this study to verify equipment and built temperature test system of thermal storage insulation boxes. Temperature measuring points were distributed at different sites, as such, the heating curve of each point in the box was obtained. Heat preservation effect was evaluated by the average cooling time in box. The influence of the way of holding thermal storage plates and the insulating properties of the insulation box material were considered. Our study showed that the insulation property of vacuum insulation board was better than foamed PP, the cooling maintain time could be increased by 19.3% and the average cooling maintain time increased 1.74h. The temperature distribution was more uniform and stable. However, if each wall in the vacuum insulated plate insulation box was arranged with a cooling board, the box capacity would be reduced effectively. So it was necessary to consider the influence of this factor in the practical application. The cooling maintaining time of the refrigerant under the modality of side-sway was extended by 10.5% than top-sway. But the temperature difference between top and bottom of the box was large. The temperature distribution is uneven. Adding of thermal storage board on the top made the temperature declined 2 - 3℃. The temperature distribution was more uniform when the modality of top and side were adopted, which was more conducive to the preservation of fruits and vegetables. The temperature of each point when the box was loaded and unloaded was compared, and the cooling maintaining property was analyzed, the cooling maintaining time of load decreased 0.7 h than unload. In the actual application process, all factors which affect the quality of the goods and reasonable selection of the pre-cooling temperature, the amount of refrigerant and pre-cooling temperature of the refrigerant should be considered.