Experimental Research of Drying Characteristic of Red Banana in a Single Slope Direct Solar Dryer Based on Natural and Forced Convection.

Abstract

SUMMARYResearch backgroundTraditionally, open sun drying method serves to dry the products for long time preservation. Solar drying is also employed to minimise the drying time to achieve the required moisture content. This method inherently contains complex heat and mass transfer mechanisms, which makes difficult to describe drying kinetics at the micro level.Experimental approachIn this paper, research is carried out to investigate the drying of 5 mm thick slices of red banana (Musa acuminata ’Red Dacca’) in a single slope solar dryer based on natural and forced convection. Based on the experiments, a new semi-empirical thin layer drying kinetics is proposed and compared with other existing models. The proposed model with the correlation coefficient (R2) of 0.997 is in very good agreement with other well-known models. Based on the model, we calculated the moisture diffusivity and activation energy of the red banana drying process.Results and conclusionsIt was found that the moisture diffusivity of the red banana samples was in the range 0.87-1.56·10-9 m2/s for natural convection solar drying and 0.84-2.61·10-8 m2/s for forced convection solar drying. The activation energy of the red banana varied from 24.58 to 45.20 kJ/mol for passive and 22.56 to 35.49 kJ/mol for active drying. Besides, we carried out energy and exergy analyses of red banana in the dryers and found that the average exergy losses in the forced and natural convections were 16.1 and 6.63 kJ/kg and the average exergic efficiency of the natural and forced convection dryers was 57.7 and 70.9%, respectively.Novelty and scientific contributionA single slope direct solar dryer was designed and built to maintain the desired temperature for a specified period in both natural and forced convection mode. A novel drying kinetics model with higher correlation coefficient (R2) than the other drying kinetic models is proposed for the preservation of red bananas.