Numerical simulation of heat pump thin layer drying of Amaranth leaves

Abstract

ABSTRACT Dried foods are higher in nutrients than their fresh counterparts. Numerical modeling, such as computational fluid dynamics (CFD), can be used to simulate the drying process and its method, thereby the effort to fine-tune the physical experimentation can be minimized considerably. In the present study, a CFD simulation model is developed based on the experimental investigation of the drying of Amaranth leaves in the CFD optimized drying chamber of a heat pump dryer (HPD). The distribution of the fluid domain and the influence of various circumstances on heat and mass transfer are investigated. In order to solve the mass transfer equation, an external model is developed in “C” language for the source term of moisture generation in the moisture transport equation and energy equation. This external model is then linked to the model using a user defined function (UDF) in the FLUENT CFD software. The calculated and measured drying temperature and moisture fraction are presented as a function of drying time. The obtained transient simulation results of the drying process are validated with the experimental results. The results of the CFD simulation are in accordance with the experimental results as per the physics of the problem. The maximum deviation between the experimental and CFD moisture-time plot is observed to be less than 8%. The difference between CFD and experimental results is attributed to temperature assumption, heat losses, and air leakage in the drying chamber. The new CFD methodology established in this study can be utilized as a generic procedure for evaluating the effectiveness of a HPD for drying various types of leaves.