Exploration of heat and momentum transfer in turbulent mode during the precooling process of fruit

Abstract

Developing a simulator is a prevalent method for the study of any process in which various phenomena occur simultaneously, such as the precooling process; it is also necessary in package designing. During the precooling process of fruit and in the case of large packages at high airflow rates, the flow regime inside the packages is turbulent, which is in most studies assumed to be a laminar flow that causes low prediction accuracy. In the present study, a mathematical model consisting of heat and momentum transfer in the case of a transient and a k-ɛ turbulence model, respectively, was developed in the precooling process of fruits. Two packages and two airflow rates were used to validate the model. The results demonstrate that the turbulence-model-based simulation of the precooling was carried out with a lower element number, within a shorter time, and with a satisfactory accuracy (R2 >.93866 & RMSE < 0.62). The model could predict the air movement between the fruit and consequently the heat transfer between the air and fruit. The simulator could be utilized to package designing and predicting the precooling time at the industrial scale to prevent the over-cooling of fruits and reduce energy consumption. Based on the results, the precooling of apples in the commercial package was conducted in both experimental and simulation methods with high heterogeneity lasting 268 and 520 min at airflow rates of 0.5 and 1.5 L s−1 kg−1p, respectively. By using the developed simulator, the new package was designed for apple through which the cooling time and heterogeneity decreased 48% and 35%, respectively, as compared with those obtained in the commercial package.