Termal performance and drying kinetics of quinoa in a mixed natural and forced convection solar dryer

Abstract

The objective of this research was to analyze the thermal performance of a mixed natural and forced convection solar dryer with multiple arc-shaped ribs coupled to the upper part of the absorber plate and to determine the drying kinetics for the drying process of quinoa (Chenopodium quinoa Willd). The mixed solar dryer is low cost and easy to build, it has an air blower system that operates autonomously with a photovoltaic panel. Thermal performance and mathematical models for drying kinetics were determined for quinoa. Performance tests were conducted for mass flow rates of 0.189 kg/min, 1.197 kg/min, 1.547 kg/min and 1.893 kg/min. The results reveal that, the maximum average thermal efficiency of the solar air heater was 77 % for an average solar irradiance of 1055 W/m2 and for a mass flow rate of 1.197 kg/min where the average drying temperature was 56 °C. The maximum average overall efficiency achieved was 23.28 % and the minimum drying time was 2.1 hours, for a flow rate of 1.197 kg/min. The mixed solar dryer has a maximum efficiency for a forced flow of 1.02 kg/min and the drying time is reduced to 68% compared to open sun drying. The Page model is the best fit for describing the drying kinetics of quinoa under forced flow conditions, and the Wang and Singh model is the best fit for natural convection drying of quinoa.