Studies on thermal sterilization of liquid foods in cans and pouches using computational fluid dynamics

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dc.contributor.advisor Farid, Mohammed en Ghani, Abdul Ghani A. en 2020-06-02T04:37:47Z en 2020-06-02T04:37:47Z en 2001 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract Temperature distribution, velocity profiles and the shape of the slowest heating zone (SHZ) during natural convection heat transfer of different liquid food materials in a two-dimensional can sitting in an up-right position and a three-dimensional can lying horizontally, were predicted theoretically. The computational fluid dynamics (CFD) code PHOENICS, which is based on finite volume method, was used for this purpose. The partial differential equations, describing the conservation of mass, momentum, and energy, were solved numerically. Saturated steam at 121 °C was used as the heating media. The liquid foods (CMC, concentrated cherry juice and carrot-orange soup) used in the simulation, were assumed to have constant properties except for the viscosity (temperature dependent) and density (Boussinesq approximation). The effect of natural convection was found to force the slowest heating zone (SHZ) to migrate towards the bottom of the can. The simulations highlight the movement of the SHZ and the formation of secondary flow, which affects the shape of the SHZ. The measured temperature at the geometric center of a can was compared with that predicted, and the agreement was reasonable throughout the whole period of heating. Sterilization of food in cans has been well studied both experimentally and theoretically, but limited works have been done on sterilization of food in pouches. In this study, natural convection heating of viscous liquid foods (broccoli-cheddar soup, carrot-orange soup and beef vegetable soup) in a uniformly heated three-dimensional pouch, were presented for the first time. The SHZ was found to migrate into a region within 30-40% of the pouch height from its bottom and at a distance approximately 20-30% of the pouch length from its widest end. Experimental measurements have been performed to validate the computed results for the temperature distribution in the pouch. These measurements were conducted at Heinz Watties Australasia Research and Development Laboratories in New Zealand, using Easteel Pilot Plant Retoit, which operates using steam at 121°C. The measured temperature at different locations in the pouch Was compared with that predicted, and were found to be in a very good agreement. The result of a simulation performed for the same pouch, but based on conduction heating, were also presented for the purpose of comparison. In all the simulations, the retort temperature was assumed to rise instantaneously and remained at 121°C. The effect of retort come-up time (the time required for the temperature of the retort to reach a selected constant processing temperature after steam is turned on) was also studied in one of the simulation and found to have a very small effect on the temperature distribution and the location of the slowest heating zone. The cooling process following the holding period, in which the food is hold for a period sufficient to kill the microrganism, was also simulated for the purpose of understanding its effect on the temperature distribution in the pouch. Thermal processing of liquid food always results in important biochemical changes such as bacteria deactivation and nutrient concentration changes. The distiibution of the live bacteria concentration and the concentrations of vitamins C (ascorbic acid), Bi (thiamin) and B2 (riboflavin) in a can and pouch filled with liquid food materials (CMC, concentrated cherry juice, carrot-orange soup and beef-vegetable soup) during thermal sterilization were obtained for the first time through numerical simulations. In these simulations, the governing equations for continuity, momentum and energy were solved numerically together with the concentration equations foi live bacteria and vitamins. Arrhenius equation was used to describe the kinetics of these biochemical changes, and it was introduced to the existing softwaie package PHOENICS using a FORTRAN code. The simulations show that, the concentration of the live bacteria and vitamins in a can depends on both temperature distribution and flow pattern, while in pouches, these concentrations depend mostly on the temperature distribution. The effect of using different sterilization temperature on the biochemical changes during thermal sterilization of viscous liquid food (concentrated cherry juice) was also studied. The concentrations of Vitamin C (ascorbic acid) and bacteria {Bacillus stearothermophilus) after heat treatment of pouches filled with liquid foods (carrot-orange soup and beef vegetable soup) were measured. The measured values were found to be in a good agreement with the values obtained from the simulations. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA9998296614002091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. en
dc.rights Restricted Item. Full text is available to authenticated members of The University of Auckland only. en
dc.rights.uri en
dc.title Studies on thermal sterilization of liquid foods in cans and pouches using computational fluid dynamics en
dc.type Thesis en Chemical and Materials Engineering en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en

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