Multi-temperature Distribution Optimization And Precise Temperature Regulation Of Refrigerated Truck

With the growth of production and circulation of fresh agricultural products in recent years, material exchange is becoming more common in local areas. The proportion of short-distance distribution using cold chain transportation increases. As an efficient transportation form, multi-temperature refrigerated trucks are widely used to transport various goods requiring different storage temperatures. Aiming at the multi-temperature refrigerated trucks with single evaporator, the study includes three aspects, the heat load calculation of compartment, the layout optimization of air supply system, and temperature control method.The thermal load of each zone is calculated to obtain the total heat load of refrigerated compartment, based on the heat transfer theory. The results show that the heat passed through the interior of the compartment wall is the main portion of the total heat load, while the respiratory heat is the secondary.The research purpose is to improve the uniformity of the temperature distribution inside the compartment. Air supply system optimization objectives include air outlet layout, air return height, air supply angle and other parameters. Consider the interaction between the factors, this paper designs a L27(313) orthogonal test. Using computational fluid dynamics method and standard k-ε model, this paper obtained the temperature field distribution inside the compartment under different conditions.The temperature data is collected for the fifteen coordinates of the multi-temperature refrigerated trucks’refrigerated zone and normal temperature zone. Evaluation of statistical analysis is irregularity coefficient. The results show that the temperature irregularity coefficient of refrigerated zone is significantly higher than that of the normal temperature zone; changes in the level of various factors have different effects on the irregularity coefficient. In no-load state, air outlet layout is the most significant factor affecting the compartment temperature distribution; in loading state, air return height is the most important factor affecting the compartment temperature distribution. By analyzing the laws of air return height affecting the compartment temperature distribution, this paper presents multi-temperature refrigerated trucks vertical rail design. The results show that vertical rails can change the state of the temperature distribution inside the compartment. Without destroying the temperature distribution of normal temperature zone, it can improve the uniformity of temperature distribution of refrigerated zone.Finally, by analyzing the working environment as well as refrigerated trucks temperature control demand, also consider the temperature control process with multi-parameter, nonlinear and hysteresis characteristics, this paper proposes the use of fuzzy control methods to achieve the compartment temperature control. Based on actual operating experience, fuzzy control rules are designed. In this paper, using Matlab software to simulate the fuzzy controller and compared with conventional PID control methods. The results show that:the fuzzy controller designed in this paper can quickly converge. Compared with the traditional PID controller, fuzzy control has a small overshoot and can quickly tuning parameters. Therefore, the fuzzy controller can be used in refrigerated trucks temperature control and improve the control accuracy.In this paper, the heat load calculation, the layout optimization of air supply system and the design of temperature control were completed. It can provide bases for the selection of evaporator and structural parameters. In addition, it provides suggestions for improving the accuracy of temperature control. This has important significance for the use and promotion of multi-temperature refrigerated trucks.