Effects of refrigerated truck temperature field uniformity on preservation of vegetables

Abstract: Social development promotes the growth of food production, thus increasing the requirement for food cold-chain circulation. The cold chain of fruits & vegetables occurs among picking, storage, and transportation and the entire process prior to consumption. It is what keeps fruits & vegetables at the appropriate temperature environment in order to maximize their storage quality assurance. Refrigerated transport has higher requirements on vehicles such as good refrigeration insulation properties free from large temperature fluctuations. Using refrigerated trucks is an advanced means of meeting the refrigerated transport development trends. Refrigerated trucks are able to meet the diverse market and the small quantities of frozen or fresh goods. Recently, the quantity of refrigerated trucks has been increasing rapidly. It is very important for refrigerated trucks to improve their uniform temperature field. The temperature field distribution of refrigerated trucks is one of the key factors that ensures a uniform distribution of the cooling capacity and it is what achieves energy reservation and weight loss reduction. Therefore, ensuring a uniform flow in the distribution of cargo area is a critical issue in improving the quality of transported fruits & vegetables. Air supply is one of the key factors that ensures a uniform temperature field distribution to keep fruits and vegetables at good quality, prolong the shelf-life of products, and reduce loss in the refrigerated transport.Therefore, the experimental system for a refrigerated truck and data acquisition system has been developed. The experimental system consists of the refrigeration system, carriage of the refrigerated truck, and the fan. The data acquisition system includes the acquisition board, acquisition program, personal computer, anemometer, and thermocouples. The temperature in the refrigerated truck can be adjusted by the thermostat based on the different temperature requirements. To assess the temperature distribution in the refrigerated truck, the temperature non-uniformity (S) has been defined. In this paper, three kinds of vegetables (baby cabbages, peppers, and flammulina velutipes) have been tested in the refrigerated truck under different conditions. The weight loss rate, membrane penetration rate, vitamin c content, and chlorophyll content were evaluated under different storage conditions with three kinds of air supply forms. Weight loss rate, membrane penetration rate, and vitamin c content were evaluated under different storage conditions with different temperature fields, with temperature non-uniformity values of SI=3.71, SII=5.68, and SIII=8.36. It was found that the effect of the temperature field on the quality of vegetables is significant. Results show that the uniform temperature field has a better effect on preservation. The reason for this is that the more uniform the temperature is distributed, the more uniform the cold energy is distributed. In doing so, vegetables can be kept at the appropriate temperature environment; thus, the quality of vegetables can be kept for a long time. The three kinds of vegetables (baby cabbages, peppers, and flammulina velutipes) show the same result. This study can provide a reference for the optimization design of the refrigerated truck. The results can contribute to improving the quality control of vegetables or agricultural products during the process of refrigerated transport.