A study of radiation and natural convection of air on drying of coffee beans in a heat recovery solar dryer

摘要

A solar heat recovery dryer for drying coffee beans was designed and tested based on heat recovery through condensation. A mathematical model of the dryer was built based on heat and mass transfer, fluid flow and boundary analysis. Experimental data from the first run was used to estimate two critical constants in the model, and seven subsequent runs at different conditions were used to validate the model. The simulated results and the experimental data correlated well (r = 0.97). Design of the solar heat recovery dryer was then optimized in terms of annual profit, estimated from operation, maintenance, construction and product costs. The three parameters optimized were the dryer height, length, and the depth of the coffee bed. A sensitivity analysis of the profit equation showed that the tray area, density of coffee beans and the price of labour had the most effect on profit. From this, a suitable design of the solar heat recovery dryer was developed for local conditions.