Experimental performance and modeling of a greenhouse solar dryer for drying macadamia nuts

Abstract

This paper presents experimental performance and modeling of a greenhouse solar dryer for drying macadamia nuts. The dryer consists of a parabolic roof structure covered by polycarbonate sheets on a concrete floor. Dimension of the dryer is 9 m in width, 12.4 m in length and 3.45 m in height. Six 15-W DC fans powered by two 50-W PV modules were used to ventilate the dryer. The dryer was installed at a macadamia nut producer in Loei Province, Thailand. To investigate its performance, the dryer was used to dry six batches of macadamia nuts. For each batch, 730 kg of in-shell macadamia nuts was dried in the dryer. Results obtained from this investigation showed that drying air temperatures in the dryer varied from 30°C to 65°C. The drying time for macadamia nuts was within 5 days and good quality dried product was obtained. To model the performance of the greenhouse solar dryer, a system of partial different equations describing heat and moisture transfer during drying of the macadamia nuts in the dryer was formulated. This system of partial differential equations was solved numerically using the finite difference method. The simulation results agreed well with the experimental data for solar drying of the macadamia nuts. The estimated of payback period of the dryer is 1 year.