ABSTRACT
The research presents the design and development of indirect passive solar dryers, equipped with paraffin and used engine oil as thermal storage material embedded in a heat exchanger copper pipe, which runs from the collector to the drying chamber. The dryers were operated and tested under ambient conditions of temperature and relative humidity ranges of 29.1-40.2^oC and 27-90% respectively. Paraffin and used engine oil thermal storage material has a temperature of 10.8°C each above ambient temperature at noon time which kept the product drying. Collector of dryer-a has the highest recorded efficiency of 26.67% as a function of the presence of the paraffin oil available as the thermal storage material in the heat exchanger pipe. Pre-treated ginger slices with 30seconds, 60 seconds, and 90seconds boiling water were used to test, compare and select dryer A as the best dryer based on standard dryer performance parameters. Dryer A equipped with paraffin oil produced 0.016MJ of energy with total useful energy of 1.30MJ reduced moisture content of ginger from 82.14%wb to 7.14%wb within 15 hours, while Dryer B with used engine oil produced 0.009MJ of energy with total useful energy of 1.29MJ dried similar product for 16 hours. Dryer A shows shorter drying time while Dryer B and C which carries air showed greater average exergy efficiency of 44.9% and 55.6% respectively. Pre-treatment and drying time showed statistical significant effect on moisture content at 5% probability level. Finite difference method was used to solve and simulate the heat and mass transfer equations of the selected dryer. The numerically simulation under natural convection using COMSOL multi physics software showed a perfect modelling of the system. Drying temperature, relative humidity and moisture distribution of the ginger slices where predicted and compared with experimented results with R² values of 0.67, 0.61 and 0.95 respectively.