Study On Temperature Field Simulation In Refrigeration Container And Its Applicability Evaluation System

Refrigerated truck is an important transport of perishable food cold chain transport, but the temperature field distribution inside the compartment is not clear, lack of applicability evaluation system, which seriously restricts the refrigerated vehicle manufacturing precision and the practical benefits. In this paper, a city refrigerator car with a volume of 4.5m* 1.9m* 1.9m is studied. The dynamic heat transfer mechanism of refrigerator cars’ inner and outer wall and the temperature field distribution are studied. The diversion structure of the temperature field in the compartment is improved, and the uniformity of the temperature field is improved, which provides a theoretical basis for the optimization design of the structure of the refrigerated compartment. The relationship between the temperature field and the temperature, the speed of the car and the thickness of the car body are studied. The applicability evaluation system of temperature field in refrigerated compartment is constructed. A refrigerated vehicle test bench is built to carry out the experiment on the simulation result verification of the internal temperature inside the container and applicability of the evaluation system.The convective heat transfer characteristics and the calculation method of the heat flux of the compartment wall are studied, and the change of the heat flux of the compartment wall is revealed. The influence of flow heat transfer coefficient and vehicle speed on the heat flux of the inner wall inside the compartment is studied. The results show that the average heat flux density of the compartment wall increases with an increase in the heat transfer coefficient and speed, but when the car speed reaches 5m/s, the average heat flux density increase with the speed. The average heat flux density of the external wall of the compartment was simulated. The results show that the average heat flux density difference of the outer wall surface is large, and improves with an increase in the ambient temperature. The simulation results of the average heat flux density are consistent with those of the theoretical model. The average heat flux of wall 2, 3,4,5 and 6 showed a linear increasing trend with an increase in the vehicle speed. The convective heat transfer coefficient of the inner wall inside the compartment is numerically simulated, and a method for calculating the average wall heat flux is proposed.The influence of the environmental conditions and the flow structure of the compartment on the temperature field distribution in the refrigerated compartment are studied, and the distribution of the temperature field in the stacking area is revealed. The influence of the environment temperature, vehicle speed and loading condition on the temperature field distribution in the refrigerated compartment are simulated and studied. The results show that the cooling air flow in the refrigerated compartment is gradually diverged from the main flow direction of the evaporator. In the mainstream direction, the air temperature is gradually increased. Mainstream area forms in the middle-top of the refrigerated compartment, thus the front part of the overall temperature is higher than the rear. The main air flow forms the low temperature area in the bottom corner of the car. The temperature is gradually increased along the bottom of the car. A recirculation zone is formed in the lower part of the carriage, and a local eddy current and a disturbed flow area are formed in the corner and the middle area of the carriage. The influence of the structure of the top guide structure on the temperature field is studied. The results show that under the top air supply mode, with flow guide duct and strip air outlet with the opening ratio of 30%, the uniformity of temperature field inside the compartment is improved when hanging meat. The probability distribution of the temperature field in the stacking area is studied. The results show that the probability density of the temperature field in the stack is in line with the Gauss distribution. The increase of ambient temperature causes the temperature field inside the compartment to rise and the temperature range to expand.The applicability evaluation index, evaluation system and standard temperature field evaluation model of the temperature field in the compartment are studied. The applicability evaluation system of the temperature field in the compartment is established, which includes the evaluation indexes such as the average temperature of temperature field, the nonuniformity coefficient of temperature and the temperature difference, etc., and the extended evaluation indexes such as the average deviation from temperature difference ratio, temperature uneven coefficient ratio, temperature difference ratio, etc. The mathematical model of the standard temperature field evaluation index is established. The model is characterized by the relationship between the average temperature of the standard temperature field, the temperature nonuniformity coefficient and the temperature difference, and the volume ratio. The effectiveness of the proposed model is verified by the experimental results.The temperature field test bench is developed, and the distribution of the temperature field test data in the compartment is studied. By the standard temperature field evaluation system constructed in this paper, the applicability of the test temperature field is evaluated. The temperature field test bench can simulate the natural environment temperature ranging from-10 to ～45℃ and the speed from 0 to 100km/h. The experimental results show the validity of the simulation results of the temperature field in the compartment. The probability distribution and probability density distribution of the temperature field test data are studied. The results show that the probability density variation of the temperature field test data is in accordance with the Gauss distribution, which is consistent with the distribution of the simulated results of the temperature field in the compartment. The test results of the temperature field are slightly smaller than the simulation results, and the deviation between the two kind results is less than 10%. The effect of the air supply mode on the test temperature field in the compartment is studied experimentally. The results show that the air supply with the 20mm damper is best to improve the uniformity of the temperature field. In the experiment, the high temperature region is significantly reduced, and the average temperature is decreased, which are consistent with the simulation results. The applicability of the test temperature field is evaluated by the standard temperature field evaluation system, which is a fundamental for the optimization of standard temperature field evaluation index, the evaluation index and the working conditions of temperature field in the compartment.