HEAT PENETRATION PARAMETERS AS INFLUENCED BY NEEDLE THERMOCOUPLES AND REMOTE TEMPERATURE SENSORS IN 211 × 300 THREE‐PIECE CAN SIZE
Authors: KHURANA A. , AWUAH G.B. , WEDDIG L.M. , BALESTRINI C.G. , PODOLAK R. , SHAFER B.D. 
Published: December 2008

Heat penetration studies were conducted to investigate the effect of potential heat transmission error on the heating factors as a result of internal mounting of remote sensors in 211 × 300 can sizes. The applicability of established correction factors to heat penetration data from the remote sensors was explored, while “new” correction factors were determined for adjusting both the lag factor (jh) and heating rate index fh.

This study demonstrates that internally mounted remote sensors in smaller can sizes (211 × 300) can enhance heating in still cooks probably because of a sensor “heat sink” effect and volume displacement (less mass) for a given headspace. Likewise, significant errors would occur if remote sensors were used in smaller can sizes (211 × 300 and smaller) for still cooks. Increasing both can headspace and retort revolutions per minute minimized differences in heating factors/process time between the thermocouple and remote sensors. For end‐over‐end agitation, remote sensors could potentially be used with extra precaution to sensor configuration, methodology used in evaluating data, and the fact that both headspace and revolutions per minute would play significant roles in dictating the magnitude of anticipated errors. Given the challenge in establishing proper conditions that minimize sensor errors, and uncertainties as to when an error gets amplified for smaller‐sized cans, the use of internally mounted remote sensors (in their present size) in 211 × 300 or smaller cans must be considered with extreme caution.

Our results show that existing correction factors for thermocoupled containers are not applicable to heat penetration data from internally mounted remote sensors. The average correction factors found for internally mounted remote sensors were 1.2 and 1.07 for jhand fh, respectively. It cannot be overemphasized that these correction factors have been determined using internally mounted miniature remote sensors for specific configurations (i.e., specific fixtures for mounting sensors) and retort operating conditions for conduction heating products. Therefore, any departure from our testing protocol, especially for different sensor sizes, mounting fixtures and can size (both diameter and height) could potentially require different correction factors.

PRACTICAL APPLICATIONS

The relevance of this study is to provide timely information to the food and other related industries where self‐contained miniature remote temperature sensors could potentially be used to design thermal processes for canned food products. Particularly useful to the food industry is the identification of the need to apply correction factors (for both lag factor, jh, and heating rate index, fh) to compensate for heat transmission errors. More importantly, the study emphasizes the need to be prudent in selecting the appropriate method for establishing heat penetration data and could serve as a guideline for setting up thermal process test designs using remote temperature sensors.