Effect of can size on heat transfer characteristics of canned viscous liquid food = ผลของขนาดกระป๋องต่อคุณลักษณะการถ่ายโอนความร้อนของอาหารกระป๋องข้นหนืด


มงคล เลิศสัทธากิจ


วิทยานิพนธ์. (2003) 94 หน้า



The objective of this work was to study the effects of the can size and its geometry on the temperature distribution and flow pattern of canned viscous liquid food during sterilization using the commercially available computational fluid dynamic (CFD) software, CFX version 5.5.1. The simulated model was developed to predict the transient temperature and velocity profiles of a model liquid food, i.e., 3 percent (w/w) carboxy-methyl-cellulose (CMC). Two different patterns of the model liquid food viscosity were assumed, constant and temperature-dependent viscosity. A Boussinesq approximation was assumed for the liquid density. The various can sizes used in this study covered the range normally used in the food industry from the smallest to the largest sizes. Flow characteristics of the liquid food with different viscosity patterns showed that convection was more dominant when temperature-dependent viscosity was assumed, especially in taller cans. The magnitude of the Rayleigh number (Ra) of constant- and variable-viscosity liquids contained in all can sizes varied with the height of the can and had the value in the range of 101-102 and 102-103, respectively. More rapid changes in the liquid flow pattern, i.e., from convection to pure conduction, were also observed when the height to diameter ratio (H/D) was greater; almost pure conduction heating was observed when H/D55.0?. The location of the slowest heating zone (SHZ) of both types of liquids was varied initially, but eventually stayed at a particular region near the bottom of the can; the location of the SHZ was also variedwith the size of the can. It was also found that the SHZ of the constant-viscosity liquid varied with the ratio of the total volume of the can to the heat transfer area (V/A); the higher V/A, the lower the SHZ, when H/D551.<. On the other hand, the SHZ of the temperature-dependent viscosity liquid in various can sizes was located at a lower height than that of the constant-viscosity liquid and varied with H/D; the higher H/D, the lower the SHZ. Due to the influence of natural convection, which obtained from the simulation, the fh value from simulation differed from the Ball and Olson’s conversion equations for the conduction heating pack