Development of indirect type solar dryer and experiments for estimation of drying parameters of apple and watermelon

In the present paper, an indirect type solar dryer (ITSD) has been developed for apple and watermelon drying. The performance of ITSD and drying kinetics of watermelon and apple slices have been analyzed. From the experimental analysis, diffusion coefficient, surface transfer coefficients and activation energy of apple and watermelon were estimated. Experimental outcomes showed that the temperature inside the drying cabinet varied with time because of frequent variation in solar intensity. The average thermal efficiency of the collector and dryer was 54.5% and 25.39% during apple drying and 56.3% and 28.76% for watermelon drying, respectively. Moisture content of apple decreased from 6.16 to 0.799 kg/kg of dry basis (db) and that of watermelon reduced from 10.76 to 0.496 kg/kg of db. Drying curve was fitted with different models of existing studies. Average effective moisture diffusivity was estimated and it was 4.28 x 10(-9) m(2)/s and 4.01 x 10-9 m(2)/s for apple and watermelon, respectively. Mass transfer coefficient is found to be in the range 1.584 x 10(-4) to 3.158x10(-3) m/s for apple and 5.17x10(-4) to 4.98x10(-3) m/s for watermelon. Heat transfer coefficient was in the range of 0.16 to 3.19 W/m(2) K and 0.52 to 5.04 W/m(2) K for apple and watermelon, respectively. Activation energy for apple and watermelon is 17.34 and 18.71 kJ/mol, respectively.