## 1 Introduction  
Refrigerated display cases effectively prevent food spoilage and prolong the sales time of food [1]. Open display cases have the advantages of a good display effect and convenience for customers looking to buy, and they are widely used in supermarkets [2, 3]. From the current research situation, the display cabinet performance research capacity mainly includes the three aspects of heat load, air curtain, and energy savings. Studies have shown that the latent heat load caused by wet air accounts for 11%, which has a great influence on the performance of the display cabinet. By studying the influence of wind speed, environmental humidity, and radiation on the wind curtain, an optimal value of air supply velocity was found, and radiation was considered to be closer to the experimental value. Researchers have compared experimental data and simulation results to find the key factors affecting the air curtain and put forward efficient and energy-saving measures to improve the air curtain. Adding fog flow to the turbulence model could improve the performance of the display cabinet. In the calculations made in most of the studies above, the display cabinet was in a no-load state, and the distribution of food temperature under a load state was not considered [2]. Vertical refrigerated display cabinets adopt a multilayer shelf design to increase the space for storing food, resulting in inconsistent temperature distribution across the different layers and a trend of gradually increasing temperature in the vertical direction from top to bottom [4; 5]. How to improve the uniformity of this temperature distribution in the cabinet has become a hot research topic for experts and scholars in recent years. The temperature distribution in a refrigerated display cabinet is not uniform. In the vertical direction, there is a temperature difference between different shelves, with the temperature from the top to the bottom shelf of the refrigerated display cabinet displaying a rising trend and the bottom shelf area temperature being the highest. In the direction of the transverse, the temperature gradient at the front end of each shelf of the leeward board and refrigerated display cabinet is relatively large. The design of the structure, such as the board, shelf, and wind curtain, is unreasonable. The problems of uneven temperature distribution and high energy consumption in vertical refrigerated display cabinets have been studied by a large number of researchers. These studies mainly focused on four aspects: improving the defrosting formula, optimizing the air curtain, optimizing the cooling system, and optimizing the structure. In terms of improving defrosting methods, defrosting with refrigerant liquid after condensation is beneficial to improving the refrigeration efficiency of the refrigeration system as compared with defrosting by electric heating. Moreover, the temperature fluctuation of food in the cabinet is smaller, which is conducive to ensuring the quality of refrigerated food, and the frost layer easily falls off. In terms of air curtain optimization, studies have optimized the speed ratio of the double-layer air curtain of a vertical refrigerated display cabinet. The optimization scheme of the double-layer air curtain velocity was determined by the method of testing and modeling. When the velocity of the outer-layer air curtain is 0.455 m/s and the velocity of the inner-layer air curtain is 0.717 m/s, it can meet the requirements of low temperature in the cabinet and minimize the cold air spill-over [4]. The optimization of the display cabinet air curtain [6; 7; 8; 9; 10], air outlet [11; 12], leeward plate [8; 13], and shelf [14; 15; 16; 17] is an important measure to improve the temperature distribution uniformity in the cabinet. [PERSON] et al.