Performance Analysis of Solar Grape Dryer with Thermal Energy Storage

ABSTRACT Fruits and vegetables constitute a major part of the food crops in developing countries. From the limited data available on post-harvest losses in fruits and vegetables, it is understood that the actual losses are much higher. The minimum reported loss is 21%, while some references indicate estimates of above 40–50% . The most notable feature is that many varieties of fruits are seasonal and many of them are consumed in their dried form to a large extent which has been made possible by the process of drying Grape is one of the world’s largest fruit crops. The world production of grapes is presently 65,486 million tones out of which India accounts for 1.2 million tones. Drying the grape, either by open sun drying, shade drying or mechanical drying, produces raisins.  Raisin production has a great important in terms of foreign trade, farmer’s income and employment. In India, its cultivation is mostly confined to western parts of Maharashtra and Gujarat, Karnataka..The largest area brought under the cultivation of grapes is in the state of Maharashtra. Considering the commercial value of raisins and concentrating on reduction in waste, if the renewable technology is available for local farmers then it will be economically benefited. At the same time to overcome the disadvantage of the intermittent nature of solar energy, if thermal energy storage system is integrated with solar dryer it could enhance the energy storage capacity and make the system suitable for continuous usage. In this work efforts have been made to develop the mixed mode forced convection solar dryer for grapes drying with thermal energy storage. The performance of the dryer has been investigated experimentally. Dryer is designed with capacity of 25 kg and consist of the flat plate collector based air heating system integrated with thermal energy storage which utilizes Paraffin wax (PCM) as phase change material. Effect of mass flow rate of air on moisture content, drying rate and drying time with and without incorporation of thermal energy system has also been evaluated. Grapes are dried with developed solar dryer to check effect on drying time for different air flow rates. The thermal efficiency of dryer has been evaluated with and without use of thermal energy storage system for grapes at different air flow rates. The raisins are tested for final moisture content and its nutrition value with the commercially available resins in the market. The result shows that drying of grapes is technically feasible in accordance with international norms for moisture content and nutrition value for raisins with reduced drying time. The moisture reduction of grapes obtained with developed dryer is from 80% to 20% in 24 sunshine hours with thermal energy storage system. Incorporation of thermal energy storage system reduces drying time from 30 sunshine hours to 24 sunshine hours for grapes with mass flow rate air 0.01484 kg/sec. Drying time reduction is observed with decrease in mass flow rate of air for grapes.