Design And Experimental Analysis Of A Direct Solar Dryer With Thermal Energy Storage Equipped With A New Heat Recovery System.

Résumé: This postgraduate thesis investigates the performance of two preliminary models of natural convection solar dryers, one equipped with a heat recovery system and the other without this system. The aim of the study is to enhance the efficiency of solar dryers by addressing the challenge of insufficient solar energy during certain periods. To overcome this limitation, a heat recovery system was integrated to reduce heat loss, and the dryers were equipped with paraffin wax (PCM) boxes for thermal energy storage, enabling effective drying even under low solar energy conditions. Experimental tests were conducted at the Applied Renewable Energies Research Unit (URAER) in Ghardaia, under real weather conditions. The initial models were subjected to no-load tests, and the internal air temperature reached 87 degrees Celsius in the solar dryer with the heat recovery system, and 65 degrees Celsius in the solar dryer without the heat recovery system. The average absorber temperatures were recorded as 75 degrees Celsius in the dryer with heat recovery and 66 degrees Celsius in the dryer without heat recovery. Performance evaluation of natural convection greenhouse dryers was conducted using peppers as drying products. Ten mathematical models were used to describe the drying kinetics of the thin layer of peppers. The results indicated that the Logarithmic and Midilli-Kucuk models were the most suitable for describing the solar drying process of the products in the tested preliminary models. The moisture content of the peppers decreased from 93% to 11% within a period of three to four days. The dryer with the heat recovery system resulted in faster drying up to one day and a gain in drying temperature approximately 30% up to 20 degrees. The efficiency of the preliminary models was determined to be 40% for the dryer with heat recovery and 30.76% for the second dryer without heat recovery. Overall, this study demonstrates the potential of integrating heat recovery and thermal energy storage systems into solar dryers to improve their performance during periods of low solar energy availability. The results provide valuable insights for improving the design and operation of solar greenhouse dryers for effective drying of agricultural products with reduced energy consumption.

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