HEAT TRANSFER STUDIES DURING FORCED AIR PRECOOLING OF PERISHABLE FOOD PRODUCTS

Abstract

The importance of preservation of perishable food products has been felt throughout the world with the rapid growth of world population and increase in all around demand for food products. In order to avoid the shortage of supply during needy hours, they may have to be preserved for long time to prevent their perishing. To maximize the efficiency of cooling and freezing operations for foods, it is necessary to optimally design the refrigeration equipment to fit the specific requirements of the particular cooling or freezing application. The design of food refrigeration equipment requires estimation of the cooling and freezing times of foods, as well as corresponding refrigeration loads. The accuracy of these estimates, in turn, depends upon accurate estimates of the surface heat transfer coefficient for the cooling or freezing operation. In this respect, accurate determination of the heat transfer parameters for the cooling operation is essential. In the present work, forced-air precooling experiments were conducted on an apple, an orange and group of apples, varying the cold air velocities. Their temperatures at three locations i.e. core, half-radius and surface, were measured and plotted against time. From this data, the convective heat transfer coefficient was calculated and a correlation between it and the cold air velocity was drawn. Further, the Nu-Re correlation was also established using the above test results.