Abstract
Open sun drying is a common method of drying of agricultural products in developing countries. Despite having several disadvantages, it is widely practised because it is a very simple way of drying. Tinospora cordifolia (a type of herb), Curcuma longa L. and Zingiber officinale (spices) were dried in the open sun and determined thermal parameters like product temperature, temperature around the product surface and rate of moisture transfer. The drying time for Tinospora cordifolia, Curcuma longa L. and Zingiber officinale were 41, 43 and 45 sunshine hours respectively with average solar radiation of 10.8MJ/m2. Convective heat transfer coefficient (h c) for Tinospora cordifolia, Curcuma longa L. and Zingiber officinale were 1.57-3.85W/m2°C, 2.32-3.42W/m2°C and 1.62-3.34W/m2°C respectively, and increased by raising the difference in temperature between the product and the temperature around the product surface (T) from 0.3°C to 8.1°C. A fair agreement was observed between fitted and experimental results with coefficient of correlation ranging from 0.9984-0.9921, 0.9960-0.9856 and 0.9983-0.9898 for product temperature, temperature around the product surface and moisture content during drying.
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