Evaluation of Convective Heat Transfer Coefficient of Herbs Dried in a Mixed Mode Solar Dryer

A mixed mode forced convection solar dryer (MFSCD) integrated with double pass counterflow solar air heaters was developed in-house for drying of high valued Moringa Oleifera and Stevia rebaudiana leaves. Experiments were carried out to evaluate the convective heat transfer coefficient of the samples in the developed solar dryer and under open sun drying (OSD). From the analysis, the average convective heat transfer coefficient of the leaves in the MFSCD are found to be 4.93 and 4.22 W/m2-K for Moringa and Stevia leaves and in OSD the average values are 1.31 and 1.25 W/m2-K, respectively. The efficiency of the mixed mode solar dryer was found to be 26.4 %. The proximate analysis for the protein and fiber content of the experimental samples concludes that the crude protein and crude fiber of solar dried samples are better than the sun-dried ones.