CFD Simulation of Airflow and Heat Transfer During Forced-Air Precooling of Apples

In this work, we study how different air-inflow velocities affect the apple-temperature distribution during forced-convection cooling of individual apples by simultaneously modeling airflow and heat transfer. In general, an increase in airflow velocity increases the cooling rate and heat transfer fluxes across the apple surface and decreases cooling time. The results show that a reasonable increase in cooling rate is obtained with an increase in airflow velocity to 2.5m/s; any further increase in airflow velocity simply wastes energy because it leads to a relatively low increase in cooling and heat transfer fluxes across the apple surface. By comparing the temperature simulated with and without accounting for respiratory heat, the maximum temperature difference is approximate to 0.033 K during cooling. Therefore, respiratory heat has a negligible effect on the temperature variations of fruit. The model was verified by comparing its results with those of experiments. The predicted results are consistent with the measured results. Practical ApplicationsTo ensure the quality and safety of horticultural products and extend their storage and shelf life across the entire cold chain, a critical step in the postharvest cold chain is the rapid precooling after harvest to remove field heat. In this work, we investigate how to improve the cooling rate and minimize the cooling time during forced-convection cooling of apples. In addition, the effect of respiratory heat on temperature variations of fruit is also studied. This research provides not only a more detailed understanding of flow distribution and temperature variations of fruit during cooling, but also a reliable theoretical basis for minimizing unnecessary energy consumption during forced-convection cooling of produce.