Influence of sample size and shape on transport parameters during drying of shrinking bodies

An experimental investigation on the influence of sample size and shape on heat and mass transport parameters under natural convection air-drying is presented. Potato cylinders with length of 0.05 m and thicknesses of 0.005, 0.008, 0.010 and 0.016 m, and circular slices with diameter of 0.05 m and thickness of 0.01 m were dried in a laboratory scale hot-air cabinet dryer. Results indicate that each transport parameter exhibits a linear relationship with sample thickness. Convective heat and mass transfer coefficients (h(c) and h(m)) decreased whereas moisture diffusion coefficient (D-eff) increased with increasing thickness. Considering no sample shrinkage effect in the parameter analysis, for the thickness range considered, the values of h(c) are found to be underestimated in the range of 29.0-30.6%, whereas those of h(m) and D-eff are overestimated in the range of 33.7-38.0% and 75.9-128.1%, respectively. Using Levenberg-Marquardt algorithm for optimization, a correlation for Biot number,for mass transfer (Bi-m) as a function of drying time and sample thickness is proposed. A close agreement was observed between dimensionless moisture contents predicted by this relation and those obtained from experiments for different sample thicknesses at drying air temperature of 60C For the same thickness and drying conditions, circular slices caused an increase in each transport parameter significantly.