Performance evaluation and economic feasibility of a solar-biomass hybrid greenhouse dryer for drying Banana slices

Abstract

A greenhouse dryer consisting of drying chamber, drying trays, biomass unit and heat exchanger was used in this study. Three energy modes were considered namely solar, biomass and solar-biomass. The dryer performance was evaluated based on drying air properties, drying rates, energy efficiency, energy utilization and exergy efficiency. During drying, the temperature difference between inside and outside was found to be 12.96 ± 5.25, 8.88 ± 1.38 and 13.21 ± 6.21 °C for solar, biomass and solar-biomass modes, respectively. This had a corresponding relative humidity difference of 8.76 ± 8.28, 24.26 ± 8.83 and 27.51 ± 10.24%, respectively. The mean drying rates were found to be 0.28 ± 0.04, 0.21 ± 0.03 and 0.23 ± 0.06 g/gdm/hour for solar, biomass and solar-biomass modes, respectively. The results showed significant difference between means of the drying rates of banana slices for the three energy modes. Further analysis showed insignificant difference between drying rates of solar and solar-biomass as well as biomass and solar-biomass. Energy efficiency and exergy efficiency for solar mode were found to be lower than that of biomass and solar-biomass modes. In addition, average energy utilization ratio in the greenhouse dryer was noted as 35.58 ± 24.78, 40.60 ± 10.52 and 33.46 ± 13.45% for solar, biomass and solar-biomass modes, respectively. The corresponding average hourly exergy efficiency of drying air was found to be 64.60 ± 24.78, 59.37 ± 10.52 and 66.50 ± 13.47%, respectively. There was no statistical difference between the exergy efficiency of drying air for the three energy modes used. The payback period of the dryer was found to be <1 year which is lower than expected life of the dryer (4 years).