Numerical Analysis of Air Supply Alternatives for Forced-Air Precooling of Agricultural Produce

Precooling agricultural produce is an intensive, energy-consuming process. To improve the efficiency of forced-air precooling and ultimately contribute to energy sustainability for postharvest storage of fresh produce, we designed three alternative air supply systems, simulated their cooling performances over a 96 h precooling process in a cold storage facility storing Chinese cabbages, and then compared their performances with a conventional design. All models were developed on a large scale on the basis of validated computational fluid dynamics models. The horizontal air supply scheme shortened the seven-eighths cooling time by 18.8%, and its maximum cooling rate increased by 19.7% compared to the conventional air supply scheme. The seven-eighths cooling time under another alternative design, the vertical air supply scheme, was 9.4% lower than the conventional, with the maximum cooling rate increasing by 10.5%. However, the maximum cooling rate of the last alternative design, the perforated ceiling air supply system, was 6.6% less than the conventional scheme, resulting in a 6.3% longer seven-eighths cooling time. The heterogeneity index of temperature implied that the horizontal air supply offered better overall cooling uniformity than the other designs, which can be attributed to its evenly distributed airflows and well-organized air movement paths, based on the combined analysis of temperature contours and air velocity contours at selected planes. Our findings are expected to provide practical guidelines for the refinement of the air supply system to improve its energy sustainability in forced-air precooling.