Evaluation of convective heat transfer coefficient during drying of shrinking bodies

The convective heat transfer coefficient during drying of shrinking bodies is evaluated using an insulated laboratory scale cabinet dryer under natural convection conditions. Drying experiments were performed on cylinder shaped potato samples of diameter 0.01 m and length 0.05 m for air temperatures 40, 50 and 60 degrees C. The heat transfer coefficients with and without shrinkage effect were determined as a function of drying time. The results reveal that the heat transfer coefficient with shrinkage is higher than that obtained without shrinkage and becomes almost double at the end of the drying period It is also observed that the moisture content of the sample and the drying air temperature have significant influence on the heat transfer coefficient. In order to obtain a functional relationship between the ratio of the heat transfer coefficients with and without shrinkage and the dimensionless shrinkage parameter, a correlation is developed. The experimental data have also been correlated by an equation of the form Nu = CRan. The numerical values of the heat transfer coefficient during drying are found to be in close agreement with those reported in the literature. (c) 2005 Elsevier Ltd. All rights reserved.