Numerical modeling of periodic airflow reversal with variable air supply velocity for optimal forced-air cooling of apples

Abstract

Airflow distribution inside fruit packages is the primary factor responsible for improving the cooling characteristics of a forced-air cooling system. Often, while focusing on one cooling parameter optimization, the effects of other cooling parameters are ignored, which are essential for an optimized cooling system. The present study analyzed the effects of flow velocity variations combined with flow reversals on primary cooling characteristics (i.e., cooling rate, cooling uniformity, and energy consumption) with both individual and multi-parameter optimization using numerical modeling. A simulation approach is proposed for combined velocity variations and flow reversals, providing consistent results with the experimental data. Fifteen cooling plans were formulated based on the number of flow reversals, reversal frequency, and velocity variation analysis. The analysis shows that energy consumption based on pressure drop increased significantly when airflow velocity exceeded 2 m/s. The cooling rates were higher for higher velocity (i.e., 3 m/s); however, the energy consumption tripled when compared to 2 m/s. Therefore, some cooling strategies are suggested based on cooling rates and energy consumption, and appropriate compromises are made between both for an optimal system. Similarly, optimized cooling strategies were selected based on cooling uniformity analysis with different tools. The overall heterogeneity index calculated based on three-dimensional surface heterogeneity maps showed the highest uniformities in all plans involving flow reversals. Finally, some novel cooling strategies are proposed from cooling plans analyzed using multi-parameter optimization, considering cooling rates, cooling uniformity, and energy consumption as primary performance parameters.