Thermal Time Distributions in Tubular Heat Exchangers during Aseptic Processing of Fluid Foods

Abstract

AbstractThe objectives of this study were to develop a mathematical model for thermal time distributions (TTD) in tubular heat exchangers and to perform a computer simulation to study the role of TTD in food process design. A computer simulation of heat transfer to a pseudoplastic fluid with variable thermophysical properties heated in a tubular heat exchanger was carried out. A power law model, with the flow behavior consistency indices modeled as temperature‐dependent properties, is used to described the flow behavior of the fluid. The coupled continuity, momentum, and energy equations with corresponding boundary conditions for constant wall temperature and heat flux are solved numerically by a Dufort‐Frankel finite difference technique. Thermal processing models are then applied to obtain TTD by tracking fluid elements along the flow path in a heating section. TTD and F curves are used to evaluate process effectiveness. Two tube radii (0.0254 and 0.0382 m) and two wall temperatures (125 and 130 °C) were studied. Increasing the wall temperature from 125 to 130 °C reduced the length of the heat exchanger by 11.3%. Increasing the tube radius by 150% caused an 84.2 % increase in the length of the heating section.