Conjugate modeling of flow and simultaneous heat and mass transfer in convective drying of porous substances

An in-depth understanding of the convective drying mechanism is significant for improving industrial production efficiency and reducing available energy consumption. In this research, a conjugate numerical model appropriate for representing the convective drying is developed and incorporated into the computational fluid dynamics framework, which adopts a non-equilibrium approach to depict the thermal transfer between the hot air and wet porous substances. The thermophysical properties of wet porous substances are formulated to change dynamically in response to the variation of moisture content. A concept of two-resistance dynamic equilibrium is introduced to characterize the interstitial mass exchange between phases, in which the void surfaces of wet porous substances are treated as phase interfaces. That numerical model is then validated by simulating the convective drying of apple slices for different airflow conditions. Calculation results show that the numerical model is capable of accurately predicting the time history of moisture content. The simulative results are in excellent agreement with experimental data as well. The flow distribution of field variables, the non-equilibrium thermal transfer, and the interstitial mass exchanges are also effectively captured. It indicates that the present conjugate numerical model can predict the pivotal physical phenomena involved in convective drying.