An Empirical Methodology for Evaluating the Fluid to Particle Heat Transfer Coefficient in Bi-axially Rotating Cans Using Liquid Temperature Data

Abstract

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°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 (3×3 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 .

Effect of Process Variables on Heat-Transfer Rates to Canned Particulate Newtonian Fluids During Free Bi-axial Rotary Processing

“…A methodology was established (Dwivedi and Ramaswamy 2008) to overcome this problem and evaluate the heat-transfer coefficients associated with free axial rotation using an empirical approach. The technique involved first obtaining a relationship between U and h fp in the fixed axial mode and assuming a similar relationship would exist in the free axial mode.…”

“…Models were developed in the previous study (Dwivedi and Ramaswamy 2008) for U and h fp under fixed axial rotation to get h fp /U values for a limited range of experiments. However, in order to be able to use them under a broader range of experimental conditions, additional data over a broader range of processing conditions are needed so that more comprehensive models could be developed relating U and h fp in fixed axial mode.…”

“…The other two cans held at the opposite end were restrained all the way and, therefore, provided fixed axial mode (only rotating with the cage). Additional details of the modification are provided in Dwivedi and Ramaswamy (2008).…”

“…In the free axial mode, the liquid temperatures were measured using Track Sense® Pro (Ellab Inc., Centennial CO), an FDA-compliant wireless multi-channel data-logging system. Additional Dwivedi and Ramaswamy (2008).…”

“…Traditional computation of U and h fp , however, require data on both particle and liquid temperatures. In a previous work (Dwivedi and Ramaswamy 2008), a useful methodology was established for evaluating U and h fp in free axially rotating cans under commercial processing conditions. The method involved developing correlations between h fp and U using real timetemperature data gathered from test cans in the fixed axial mode of rotation and then coupling them with experimentally evaluated U from fluid temperature gathered with wireless sensors to compute h fp for bi-axially rotating cans.…”