Unsteady Heat Transfer for Package in Refrigerated Room with Free-forced Combined Flow

Abstract

To investigate the heat transfer phenomena for a food package in a refrigerated room with upflow or downflow, temperature distributions in the package were numerically calculated using fundamental equations. These equations were derived under certain assumptions in the case where one side wall of the package was in touch with the duct and gas flowed upward or downward through the duct, while the other side walls were insulated as a model of the package wall in the refrigerated room. The temperatures were solved for an unsteady state using the empirical equation for the heat transfer coefficient.
The temperature at the front surface of the package remarkably decreased in the beginning and then only slightly decreased with elapsed time. The average heat transfer rate from the package to ambient fluid in upflow was about two times larger than the one in downflow. This meant that the cooling time of the package by upflow could be shortened by half of the downflow one.
To check these calculated results, the temperature distributions were experimentally measured under the same operating conditions as those of the theoretical analysis. The calculated temperature distributions agreed closely with the measured ones.