Adsorption and regeneration characteristics of composite desiccants

Solar dryers are economical for crop drying and are environmental friendly. However, in tropical region due to high humidity of ambient air the efficiency of solar dryer gets reduced. Desiccants can be used for reducing the humidity of ambient air. In the present study, three desiccants viz. silica gel, bentonite clay and activated carbon were selected and tested for their use to improve efficiency of solar dryer. The composite desiccant mixture was prepared by mixing three selected desiccants in different ratios and was evaluated for adsorption and regeneration characteristics. The adsorption rate of different composite desiccants was calculated at 2 h interval. The regeneration rate of composite desiccants was studied at a temperature of 50°C and 55°C and the data were recorded at 1 h interval. The evaluation was done at three weightage levels of adsorption rate: regenerate: unit cost i.e. 50: 30: 20, 60: 20: 20 and 40: 40: 20. The maximum value of performance index at three weightage levels based on highest adsorption rate and regenerate rate and lowest unit cost was observed as 1.66, 1.5 and 1.81. The treatment T (Silica gel 100%) was found as better desiccant among the selected composite desiccant with average adsorption rate 1.49%moisture per h followed by T₅ (Silica gel 80%, Activated 20%) with 1.46% moisture per. The statistical analysis showed that the performance efficiencies of silica gel were observed highest 84.33%, 77.33%, and 91.7% at different weightages of adsorption rate, regeneration rate and cost of composite desiccant.