Determination of constant and variable thermal diffusivity of cashew pulp during heating: Experimentation, optimizations and simulations

Abstract

Cashew nut is used by the industry in the production of roasted kernels, whose flavor is appreciated in various parts of the world. However, the production of 1 ton of roasted kernels generates up to 15 tons of cashew apple, which is a highly perishable by-product. To increase its shelf life, cashew apple can be transformed into pulp, which is then pasteurized. Designing efficient pasteurizers requires knowledge of the thermal diffusivity of this product, in the heating step. Thus, an experiment was carried out with heating of this pulp placed in a metallic cylinder (from 25.6 °C to 63.1 °C), in a water bath (at 63.1 °C), with a thermocouple fixed at the central point of the product. Thermal diffusivity was determined through the inverse method, using analytical and numerical solutions of the diffusion equation. The use of a variable thermal diffusivity, given as a function of the local temperature, expressed by α(T) = a1cosh(a2T2), produced excellent fit of the simulation to the experimental data, with random distribution of errors, and with χ2 = 0.1626 and R2 = 0.999984.