Heat transfer analysis during mixed-mode solar drying of potato cylinders incorporating shrinkage: Numerical simulation and experimental validation

Heat transfer analysis during mixed-mode solar drying of foodstuff is crucial in food industries now-a-days as better understanding of the phenomena will assist in suitable design and optimization of the drying process parameters. In the present work, natural convection mixed-mode solar drying experiments were carried out with potato cylinders of varying diameters (8, 10 and 13 mm) with a fixed length of 50 mm. The convective heat transfer coefficient, hcon was evaluated without and with the incorporation of shrinkage effect in the mathematical model. The results predicted that consideration of sample shrinkage led to an overestimation of average values of convective heat transfer coefficient, h¯con by 55.72-61.86% for the investigated samples. It was also observed that the moisture content and sample diameter had a notable influence on heat transfer coefficient. Heat transfer correlations in terms of dimensionless numbers were developed for each sample diameter by an equation of the form Nu = C(Ra)n. The uncertainty in the average value of hcon was found to lie in the range of 1-3%. A finite element based COMSOL Multiphysics software was used to develop a numerical model to project the transient sample temperature during the drying process. The predicted sample temperatures considering shrinkage were in close agreement with the experimental results showing lower values of statistical errors.