Optimal Design and Performance Analysis of Hybrid Solar PVT Dryers Integrated with Phase Change Materials for Agri-Food Preservation

Abstract

This thesis investigates the performance of four prototype solar dryers operating under both natural and forced convection modes. The systems are classified into two natural convection models and two forced convection models. The first is a solar dryer based on natural convection, the second utilizes forced convection, while the third and fourth incorporate a heat recovery system under natural and forced convection, respectively. The study aims to enhance the efficiency of solar dryers by addressing the challenge of limited solar energy availability during specific periods. To mitigate this, a heat recovery system was integrated, along with paraffin wax (PCM) thermal storage units, to minimize heat losses and enable effective drying even under low solar irradiance conditions. Experimental testing was conducted under real atmospheric conditions at the Laboratory of New and Renewable Energies in Arid and Saharan Areas and the Laboratory of Process Engineering at the Scientific Research Center, Kasdi Merbah University, Ouargla. Under natural convection, the maximum internal air temperature reached 90.1 °C for the dryer equipped with heat recovery, compared to 73.8 °C for the conventional system. The average absorber temperature was 69.2 °C with heat recovery and 62.5 °C without. Lemon slices were used as the drying product, and ten mathematical models were employed to describe thin-layer drying kinetics. For forced convection models, the internal air temperature reached 103.1 °C with the heat recovery system, and 84.8 °C without. The average absorber temperatures were 90.1 °C and 79.6 °C, respectively. Moisture content in lemon decreased from 94% to 10% within 8 to 9 hours. The heat recovery system enabled faster drying (up to 6 hours) and increased drying temperature by approximately 20 °C. Thermal efficiency was found to be 40% for the system with heat recovery and 30.76% for the one without. Overall, the study demonstrates the potential of integrating heat recovery and thermal storage systems into solar dryers to improve their performance, particularly for greenhouse agricultural applications and in periods of limited solar availability.