Non-linear heat and mass transfer in packed spherical horticultural produce: Heterogeneity and irreversibility

Abstract

Heterogeneous distribution of heat generation from respiration reaction inside produce as well as irreversibility from different sources are still not analyzed especially for non-linear phenomena with different external operating conditions and internal produce properties. In this study, a numerical model of coupled heat and mass transfer with reaction kinetics of respiration is developed for packed spherical postharvest produce. We then analyze the distribution and irreversibility of respiration heat inside them under different inlet velocity, gas diffusivities and reaction rate of aerobic and anaerobic respiration. The result shows that non-linear distribution of respiration heat is identified as the transition of dominated mechanisms from convective mass transfer and diffusion of O2 resulting in local peaks between produce surface and center to convective cooling and thermal conduction leading to peak convergence with decreasing values near produce center. Increasing inflow air velocity causes reduced heterogeneity of respiration heat and earlier transition with shorter duration. Furthermore, in response to different gas diffusivity and respiration rate, non-linear variations of distribution characteristics for respiration heat are obtained by coupling effects of heat and mass transfer with complex reaction kinetics. While airflow and heat transfer processes are the main irreversibility sources, non-linear variations of entropy generation for mass transfer and respiration reaction are also obtained under external and internal influence.