Experimental study of the performance of solar dryers with pebble beds

• Published in: Energy sources 1997-07, Vol.19 (6), p.579-591
• Main Authors: HELWA, N. H., REHIM, Z. S. ABDEL
• Format: Article
• Language: English
• Subjects: Applied sciences; composite materials; dryers; efficient dryer; energia solar; energie solaire; Energy; Equipments, installations and applications; Exact sciences and technology; Natural energy; packed bed modeling; pebble bed; secadoras; sechoir; Solar energy; solar energy storage; Solar thermal conversion
• ISSN: 0090-8312; 1521-0510
• DOI: 10.1080/00908319708908874

Major problems of the arid region are transportation of agricultural products and losses due to spoilage of the products, especially in summer. This work presents the performance of a solar drying system consisting of an air heater and a dryer chamber connected to a greenhouse. The drying system is designed to dry a variety of agricultural products. The effect of air mass flow rate on the drying process is studied. Composite pebbles, which are constructed from cement and sand, are used to store energy for night operation. The pebbles are placed at the bottom of the drying chamber and are charged during the drying process itself. A separate test is done using a simulator, a packed bed storage unit, to find the thermal characteristics of the pebbles during charging and discharging modes with time. Accordingly, the packed bed is analyzed using a heat transfer model with finite difference technique described before and during the charging and discharging processes. Graphs are presented that depict the thermal characteristics and performance of the pebble beds and the drying patterns of different agricultural products. The results show that the amount of energy stored in the pebbles depends on the air mass flow rate, the inlet air temperature, and the properties of the storage materials. The composite pebbles can be used efficiently as storing media.