Drying characteristics, energetic and exergetic investigation during mixed-mode solar drying of pineapple slices at varied air mass flow rates

Abstract

Present work is focused on the assessment of energy and exergy flow in a mixed-mode solar dryer during the drying of pineapple slices by utilizing first and second law of thermodynamics. Moreover, drying kinetics and effective moisture diffusivity with shrinkage correction were also investigated at natural convection (NC) and forced convection (FC) conditions. The initial moisture of pineapple slices (90%, wb) was reduced to 29.66, 23.06, 24.05 and 19.68% (wb) in 6.5 h under NC, air mass flow rates of 0.006, 0.01 and 0.015 kg/s, respectively. Results revealed that diffusivity determined by assuming negligible shrinkage demonstrated 3.5–5.3 times overestimation than shrinkage consideration. Energy analysis exhibited that about 55–78% of total input solar energy constituted thermal losses from the absorber plate. Remarkably, an increase of air mass flow rate caused an augmentation in useful heat gain by air and a simultaneous reduction in thermal losses from collector along with its efficiency improvement. Exergetic investigation of dryer identified that the exergy efficiency of the solar collector and drying chamber was positively influenced by increasing air velocity. Furthermore, exergy efficiency of the dryer for NC and drying air mass flow rate of 0.006, 0.01 kg/s was 85.45%, 46.15%, and 18.88% lesser than 0.015 kg/s, respectively.