Design, Fabrication and Experimental Testing of Indirect- Mode Forced Solar Coffee Dryer

Abstract

Considering the size and relevance of coffee industry to the Ethiopian economy an indirect, active-type, environmentally friendly, low-cost solar dryer presents the design, fabrication and experimental testing, as well as experimental investigation on forced solar coffee dryer. The solar collector and dryer system configuration has been optimized for minimal pressure drop by incorporating guide vanes and minimizing flow separation tendency during experimental testing. In addition, , thermal performance of the solar air heater was evaluated experimentally at different airflow rates on a collector with flat absorber plate and with open drying on the ground by taking the same amount of wet coffee and area that coffee in machine and on ground occupies. High collector outlet temperature and efficiency were observed in a collector with flat absorber plate. The effect of depth of grain, moisture content on wet basis, airflow rate and humidity of air were explored for parametric sensitivity during drying time. The capacity of the drying rate of the machine in kg/h are about 1.1 kg/ h and 0.53 kg/h during clear sunshine day and partial overcast sunshine day respectively. Within 6hours, coffee bean dried from 29% moisture content to12.1% on a clear sunny day and within 7hours from 17% moisture content to 11.1% on a partially overcast day. Results show that the average drying thermal efficiency of the dryer was found to be 50.6% for clear sunshine day and 36.8% for partial overcast day. A great t agreement has been observed between the experimental results and the design temperature rise predicted output with a deviation of 7.6%. Analytically predicted drying time compared with experimentally measured drying time within a 12.8% deviation. The cost-to-benefit analysis has been done and the payback period is found to be 1.05 years.