Comparison of combination mode of energy conservation for refrigerated car based on CFD numerical simulation

Abstract: Accurate temperature control is the key to achieving high quality food in cold-chain transport, and the suppliers pursue the goal of energy efficiency, emissions reduction, and transportation cost reduction. This paper takes the short distance refrigerated truck as the research object and potatoes as the experimental goods, and then establishes the calculation model for solving the temperature distribution in the refrigerated compartment. Two kinds of fan cooling temperatures (0℃ and 3℃) and cargo areas under the "blanks on both two sides and middle" stack method were used to simulate the cooling process. According to the refrigerating unit power and best refrigerating temperature of goods, the optimal time interval was defined to open and close a cooling fan in the process of transportation. Taking the wind speed at the air conditioning outlet, air-conditioner temperature, refrigerated compartment, initial temperature of the cargo area, and the physical parameters of goods as the initial boundary conditions, a 3D numerical calculated model of the car body was built by using a porous model, which took the average values of the three directions (0°, 90°, 135°) of wind speed as the actual wind velocity in a physical simulation. The unsteady numerical simulation methods of Computational Fluid Dynamics (CFD) were used to model the distribution of the temperature field in a refrigerated compartment with different stages of an opening and closing fan. The results showed that, based on the contour map of temperature field in different section of Z-axis direction, the increased rate of the cargo area temperature reduced gradually. It was suggested to add a piece of iron plate on the upper surface of the cooling fan motors, to enhance the flow strength of the front cold air and improve overall cooling rate in the goods. The change of average temperature and temperature distribution of the goods area were compared with the cooling stage and the natural convection stage. The data indicated that when the refrigeration temperature was 3℃ and cooling plus closing time of cooling fan were both 10 minutes, the energy of 3.6×105J was reduced compared with the refrigeration temperature was 0℃, cooling time was 15 min and the closing fan lasted 20 minutes. The combination was more advantageous to reduce nonessential energy consumption and improve overall transport economic benefit. The model was validated by comparing the simulation values with measured values, and the results showed that the root mean square error was 0.540℃ and the mean absolute error was 0.493℃, which showed the rationality of the design scheme and the accuracy of the selected calculation model. The study revealed the temperature distribution of goods under various cooling temperatures and cooling times in the whole process of transportation. It also provided a reliable theoretical basis for reasonable selection of the optimal combination mode of cooling fan temperature and cooling time, reducing transportation costs, and realizing energy conservation and emissions reduction.