Modelling, Simulation and Fabrication of a Hybrid Solar Dryer for the Drying of Medicinal and Aromatic Plants (MAPs)-Case Study Khyber Pakhtunkhwa (KPK), Pakistan

Abstract

Due to escalating prices of fossil fuels and their dwindling supply worldwide, solar energy is the best alternative to conventional fuels. Pakistan, being located in the sunny belt, has enormous potential for solar PV and thermal applications. Solar thermal energy can find potential applications in drying of agricultural products and medicinal and aromatic plants (MAPs) by using solar dryers. This study develops an indirect-mode forced convection hybrid solar dryer model at commercial scale and a lab scale prototype as well. Commercial scale model has been proposed after careful assessment of Maps’ drying load, equilibrium moisture content and metrological data of target areas in KPK-Pakistan, through extensive literature review and field visits. Lab scale prototype of solar dryer consists of a flat plate solar collector, drying chamber, biomass burner, heat exchanger, temperature sensors and two DC fans. Biomass burner serves as the supplement heat source in case of rainy or cloudy weather. And fans force the hot air from solar collector or biomass burner to the drying chamber, at required flow rate. Hot air moves through perforated trays inside the drying chamber from bottom inlets, and absorbs moisture from the products. Then moist air exits through the top vent. In order to predict the thermal performance of solar collector under varying ambient conditions and flow rate, a simulation algorithm has been developed. This algorithm involves matrix inversion technique in MATLAB. Modeling and simulation of dryer chamber has been done using FLUENT. Simulation results indicate the temperature distribution and velocity gradient within chamber, under testing conditions. Based on modeling and simulation results, lab scale prototype of solar dryer has been fabricated at Manufacturing Resource Center (MRC)-NUST. For experimental verification of dryer performance several drying tests were conducted for different types of MAPs, under ambient conditions. The comparison between computed and experimental results for thermal performance of solar collector and drying chamber indicated a satisfactory convergence.