A Review on Solar Drying of Agricultural Produce

Abstract, Journal of Food Processing & Technology, 2016

Open-air sun drying is a conventional source to dry plants, seeds, fruits, meat, fish, wood, and other agricultural or forest products as a means of preservation. Sun drying of crops is the most widespread method of food preservation in most part of India because of solar irradiance being very high for the most of the year. Yet, for large-scale production the limitations of open-air drying are well known. To overcome the limitations of sun-drying, solar drying technique came into existence. Solar drying also utilizes solar energy which is widely available source of renewable energy but in a different setup. The objective of a dryer is to supply the product with more heat than is available under ambient conditions, thereby increasing sufficiently the vapour pressure of the moisture held within the crop and decreasing significantly the relative humidity of the drying air and thereby increasing its moisture carrying capacity and ensuring sufficiently low equilibrium moisture content Air is heated in the collector and then partially cooled as it picks up moisture from the produce. The produce is heated both by the air and directly by the sun. Warm air can hold more moisture than cold air, so the amount required depends on the temperature to which it is heated in the collector as well as the amount held (absolute humidity) when it entered the collector. There are various classifications of solar dryer based on design criteria and mode of use i.e. active solar dryer, passive solar dryer, box dryer cabinet dryer, greenhouse dryer etc. The limitations of solar drying are also there by comparing it with modern drying techniques as it will not work during bad weather or in night and do on. By adopting different advancement techniques in solar drying, these limitations can be suppressed which will be helpful for commercialization of the technology. Keywords: Sun-drying, renewable energy, equilibrium moisture content.