Thermodynamic evaluation of heat transfer heterogeneity: Comparative case studies on air cooling methods for postharvest apples

摘要

The heat transfer during air cooling of postharvest produce tends to be heterogeneous using either room cooling or forced-air cooling due to air?ow maldistribution. The heterogeneity is typically evaluated in terms of temperature. In this study, the thermodynamic indicators, including the rates and the temporal cumulation of entropy generation and entransy dissipation, are proposed for heterogeneity analysis. Based on the experiments with postharvest apples, the heterogeneity is compared between air cooling methods using the proposed thermodynamic indicators. The temporal variation tendencies and spatial distribution characteristics of these thermodynamic indicators are further discussed. Higher heat transfer heterogeneity regarding to the rates of entropy generation and entransy dissipation is observed at the beginning stage and at the end of the process with lower temperature heterogeneity. In comparison with the entropy generation, the entransy dissipation is more appropriate for heterogeneity comparison because of the consistency. The cumulative entransy dissipation is generally higher at the locations with more air?ow and higher heat transfer rate. When compared with room cooling, the consistent reduction of standard deviation and coeffcient of variation for the cumulative entransy dissipation indicates overall lower heat transfer heterogeneity for forced-air cooling.