Simulation study of controlled atmosphere storage environment for sweet potatoes using modular turnover boxes

Abstract

Objective: To mitigate unfavorable factors during the packing, transportation, and storage of fruits and vegetables, a foldable, preassembled turnover box was designed based on the premise of recycling. Methods: Standardized boxes were used to hold sweet potatoes, which were considered long rotating ellipsoids, and the storage environment was modeled. A porous medium model, a species transport model, and a local non-thermal equilibrium model were used to study the temperature, humidity, speed, O2 volume fraction, and CO2 volume fraction distributions in the cargo area during the curing warming, post-curing cooling, and storage stages. Results： 40 ℃ was the optimum curing air supply temperature, and the time required was 5.85 h. 10 m/s was the optimum post-curing cooling air supply speed, and the time required was 8.47 h. The air supply velocity （4.0~6.0 m/s） had little effect on the distribution of O2 and CO2 volume fractions. When the air supply velocity was 4.5 m/s, the storage effect was the optimal, with deviation rates of 1.24% and 0.48% compared to the target storage conditions （12 ℃, 90.00% RH）. The generation of respiratory heat in sweet potatoes leaded to a shorter time for the internal temperature of the cargo area to reach the target curing temperature, while requiring a longer time to reach the target storage temperature. Compared to thermal conduction, convective heat transfer played a dominant role, resulting in a lag in temperature change between the internal and external temperatures of the cargo area during the storage process. Increasing the temperature and air supply velocity facilitated a faster attainment of the desired curing and storage temperatures. The physical characteristics and storage volume of sweet potatoes within the cargo area determined the subsequent warming and cooling processes. Conclusion: The velocity field on the surface of the cargo area exhibits a weak correlation with the distribution of RH, whereas the temperature field demonstrates a negative correlation with the RH field and exhibits a similar distribution pattern. The air supply velocity can alter the fluid flow direction inside the cargo area box, and both the magnitude of the air supply velocity and the direction of fluid flow inside the box significantly impact on the temperature distribution within the cargo area.

Keywords

• sweet potato
• turnover box
• porous medium
• non-uniformity coefficient
• numerical simulation
• storage