Apparent thermal diffusivity estimation of the banana during drying using inverse method

A new approach for the estimation of apparent thermal diffusivity of foods at different drying temperatures was explored, analysed and discussed in this work. Temperature versus time was obtained numerically at the center of the food (banana, "nanicao" variety) using the ID Fourier equation with drying temperatures in the range between approximately 17-65 degrees C and moisture content in the range between 0.01 and 3.43 (dry basis). The solution of the partial differential equation is made with a finite difference method coupled to an optimization technique of Differential Evolution used in inverse method. The mathematical model proposed considered the effects of shrinkage and convective heat transfer at surface of fruit. Parameters of two functions, the first dependent of the moisture content and the second dependent also of the temperature were obtained by inverse method modelling the apparent thermal diffusivity. Such parameters that provide the best least square fit between the experimental and predicted time-temperatures curves are presented in this work. This study demonstrated that a small change in the temperature and moisture content of banana cause an abrupt change in the apparent thermal diffusivity, which decrease with the decreasing of the moisture. Statistical analysis shows the excellent agreement between reported and estimated curves. (c) 2007 Elsevier Ltd. All rights reserved.