NUMERICAL STUDY OF A SOLAR GREENHOUSE DRYER WITH A PHASE-CHANGE MATERIAL AS AN ENERGY STORAGE MEDIUM

Abstract

A numerical study of the thermal behavior of a solar greenhouse dryer with a thermal energy storage unit is presented. The solar greenhouse dryer consists of a gothic metallic arch structure covered with a polycarbonate film on a metallic plate floor. The products to be dried (100 kg of banana Musa ABB CV. Kluai "Namwa") are located as a thin layer on four metallic grids. The thermal energy storage unit, disposed under the greenhouse floor, is composed of a layer of phase-change materials (PCM) placed between the metal plate and a concrete slab. Paraffin wax was used as PCM in thermal energy storage with a melting temperature of 28°C. Transfer equations are derived by considering energy balance for different components of the greenhouse dryer. The enthalpy method and heat conduction equation have been used for calculating the PCM layer and concrete slab, respectively. Equations are solved numerically by an implicit finite difference scheme and homemade software. Parametric studies of the greenhouse dryer coupled to the thermal energy storage unit illustrate the effects of drying air volume flow rate on the greenhouse temperature, drying duration, as well as the efficiency of the solar dryer and energy storage unit. Our results allowed us to conclude that under the climatic conditions of Nakorn Pathom (Thailand) the thermal storage unit improves the greenhouse solar dryer efficiency. For instance, for the drying air volume flow rate ranging from 0.05 to 0.2 m3·s-1, this efficiency varies between 12% and 38% with a thermal storage unit and between 8% and 28% without a storage unit.