Experimental investigation and numerical modeling of heat transfer during solar drying of carrot slices

Abstract

The knowledge of heat transfer analysis during drying is critical for process design, quality control and energy saving. In this study, convective heat transfer coefficient, hc during solar drying of carrot slices was determined experimentally. Carrot slices of 0.03 m diameter and 0.005 m thickness were dried in laboratory scale natural convection direct, indirect and mixed mode solar dryers. It was observed that samples dried in mixed-mode solar dryer achieved higher values of hc (24.95 W/m2 °C) followed by indirect (15.80 W/m2 °C) and direct solar dryer (13.52 W/m2 °C). Heat transfer correlations were developed during drying of carrot slices in different dryers through standard dimensionless numbers in the form of an equation Nu = C(Ra)n. The results of uncertainty analysis in the hc was observed to be in the range of 0.073%–2.7%. A numerical 2D finite element model was developed to analyse the temperature distribution inside carrot slices during drying period by using COMSOL Multiphysics simulation program. The numerical results were compared against experimental data and the outcome suggested that the sample temperatures are in close agreement with the model predictions. Lower values of statistical parameters showed better acceptability of the simulation model for predicting solar drying behaviour of carrot slices.