An empirical methodology for evaluating the fluid to particle heat transfer coefficient in bi-axially rotating cans using liquid temperature data.

摘要

An empirical methodology was developed for evaluating the fluid to particle heat transfer coefficient (h_fp) and overall heat transfer coefficient (U) in bi-axially rotating cans. Conventional particle temperature measurement during thermal processing is generally difficult in cans undergoing agitation processing and is even more difficult in cans going through bi-axial free rotation as in continuous flow turbo cookers. Thin wire flexible thermocouples have helped in gathering temperature data of both particle and liquid in end-over-end batch processes. Wireless temperature loggers have been developed for liquid temperature measurements in continuous flow systems which can be used to estimate U. Evaluation of h_fp is still difficult in these systems due to difficulty in gathering particle temperatures. The proposed method involves developing correlations between h_fp and U using real time-temperature data gathered from test cans in fixed axial mode and then coupling them with experimentally evaluated U from fluid temperature gathered with wireless sensors to compute h_fp for bi-axially rotating cans. The methodology is based on the assumption that within a can, factors that influence U will also influence h_fp, and therefore h_fp and U are generally interrelated. A three factor, five level central composite rotatatable design and a response surface methodology was used to develop the correlation models for the U and h_fp in fixed axial mode with retort temperature (111.6-128.4 degrees C), glycerin concentration (80-100%), and rotational speed (4-24 rpm) as the main factors. The developed model was used to evaluate the U and h_fp in the free bi-axial mode, using a full factorial design (3x3 factorial). The method was successfully implemented and an analysis of variance study, as expected, indicated all three major factors to influence the U and h_fp values. Glycerin concentration and rotation speed were highly significant (<0.001), while temperature was marginally significant (p<0.05) with respect to U while all factors were significant with h_fp.