Transient temperature distributions within spherical products with internal heat generation and transpiration: experimental and analytical results

Abstract

PRECOOLING is a cooling process where the field temperature of fruit and vegetables is reduced to their storage temperature in sufhcient time after harvest in the field before storage or transportation [l-3]. Experimental and theoretical studies on the determination of temperature distributions, thermophysical properties, and cooling times during precooling of fruit and vegetables are at the developmental stage. Especially in the forced-air cooling of the food products, heat and mass transfer exhibit a complicated nature because of respiration heat as internal heat generation and transpiration as a result of water loss [ 1,4]. A number of studies has been made in the past to relate heat and mass transfer analyses during cooling of food products [4-l 11. The various methods developed for calculating heat and mass transfer in fruit and vegetables have been reviewed and discussed [B]. In order to obtain a mathematical model, we consider the fact that the convective heat transfer is more signi6cant in the first case and is thus taken as the overall heat transfer coefficient; in the second case the overall heat transfer coefficient is the sum of the convection and radiation heat transfer coefficients ; in the third case the overall heat transfer coefficient is the sum of the convection and radiation heat transfer coefficients. We also consider the effect of moisture evaporation on the convective heat transfer coefficients. The objective of the present study is to obtain a methodology for the analysis of transient heat transfer during the cooling process, to determine the experimental and theoretical temperature distributions and the effective thermal properties of the product, and then to compare the computations with the experiments for four different air velocities.