Simulation and experimental verification of aseptic processing of non-Newtonian fluids under turbulent flow conditions in a tubular heat exchanger
Abstract
The overall goal of this dissertation is to improve efficiency of aseptic processing systems by developing mathematical models for soybean milk under turbulent flow conditions. First of all, rheological behavior of soybean milk at various solid contents (9%–16% w/w) was measured using an oscillatory viscometer under turbulent flow conditions in a temperature range of 60–140°C. The power law model was the most appropriate for rheological modeling of soybean milk. The apparent viscosity was not affected by flow rate. The equations describing the effects of temperature and concentration on rheological parameters (n, K) were developed within the aseptic processing temperature range. The velocity and temperature profiles of soybean milk under turbulent flow conditions were predicted in a tubular heat exchanger with the temperature-dependent physical and rheological properties by solving the coupled continuity, momentum, and energy equations with the boundary layer approximations. Through computer simulation for thermal processing of soybean milk, the desirable processing conditions that minimize the length of heat exchanger were identified to achieve the minimum processing time (F0) of 12 min and at least 90% reduction in the initial trypsin inhibitor activity. The quality index for aseptically processed soybean milk was based on the normalized a-value of Hunter's colorimeter. The color change of soybean milk due to thermal processing followed the first order reaction kinetics. The kinetic parameters for quality were determined at three different solid contents of soybean milk. The activation energies for color change were 16.5, 17.6 and 17.8 kcal/mol at 9%, 13% and 16% soybean milk, respectively. Using these kinetic parameters, quality loss due to thermal processing was predicted with simulated time-temperature data. In order to properly inactivate trypsin inhibitor and maximize quality in the thermal processing, it is necessary to pre-heat at lower temperature (below 100°C for 30 min) prior to the aseptic processing of soybean milk.
Degree
Ph.D.
Advisors
Singh, Purdue University.
Subject Area
Food science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.