DESIGN AND EVALUATION OF AN ENHANCED SOLAR DRYER USING HEAT STORAGE UNIT FOR TOMATOES DRYING

Mixed-solar dryer with heat storage unit improve the process of solar drying Roma tomatoes. This paper presents a performance comparison between two mixed-mode solar dryers. The dryers were identically designed and constructed,, however one of dryers utilized mobile and easily adjustable flat solar storage unit attached to the drying chamber during night hours to improve the drying rates after sundown(enhanced). The dryers were tested under both day and night hours. Solar insolation, Air temperature changes of ambient and drying chamber, as well as relative humidity were measured during the drying process. Rehydratation ratio, color and sensory properties were used as a parameter for the dried sample quality. Temperatures inside the dryer that utilized the heat storage unit were approximately 5 15℃"> higher than those in the normal dryer during night hours. The enhanced dryer overall showed a considerable increase in drying rate with a 33.3 and 36 % decrease in total drying time for tomatoes quarters and discs respectively as compared to the normal dryer to reach the final moisture content. Newtonian equation fitted very well the experimental data and it is possible to accurately simulate the thin layer drying behavior of tomatoes drying by enhanced dryer. Two well-defined falling rate periods and a very short constant rate period were observed. Drying constant ( k ) was greatly affected by drying air temperature and shape of tomatoes . Drying of tomatoes discs and quarters by enhanced dryer revealed good color, taste and appearance, meanwhile tomatoes halves gave unacceptable color. So, drying of halves is generally not recommended Heat storage unit permits drying to continue even after sunset or when the environmental conditions such as rainfall and high relative humidity make it difficult for normal solar drying to take place