Drying characteristics of eggplant drying in a heat pump dryer

Substantial amounts of fresh agricultural food products are lost after harvest, during handling, storage, processing, and transport. Drying is a method by which food is kept from spoilage after harvest. In the current study, a simple mathematical modelling is developed for eggplant drying to reduce the physical experimentation. The governing differential equation is converted into an algebraic equation using the finite difference implicit technique. A finite difference equation is developed for each node to determine the water content, and all of the nodal equations are solved simultaneously. Eggplant slices are dried with the aid of a heat pump dryer (HPD) in a closed-loop mode in the current study. The influence of drying air temperatures (30–60 °C), relative humidities (< 20%) and air velocities (3.5, 2.5 and 1.5 m/s) in drying (equilibrium moisture content < 10%) eggplants slices is investigated. The drying rate and drying time are significantly influenced by the air velocity. Increased drying rate with reduced drying time is observed for low drying velocity of 1.5 m/s. The drying rate curves are plotted for different drying velocities and discussed. Drying rate curves indicate that the drying process materializes mostly in the first and second falling rate periods. The results of the experimentation are in accordance with the results of many earlier research studies with the similar products listed in the references. The model is validated with experimental findings. The simulated results are consistent with the experimental data. A reasonable correlation coefficient (R-square) of 0.98 is obtained for moisture concentration of eggplant slices at different interval when comparing experimental and data derived from a numerical solution of similar agricultural production crop. The moisture concentration calculated using the numerical method assuming the convective mass transfer boundary condition matches the moisture content calculated using the analytical solution assuming the moisture content at the boundary is constant at all times. The new numerical modeling developed in this study can be used to simulate the experimental data that can be obtained from a HPD for drying different kinds of eggplant slices without conducting physical experimentation.