Liquid‐to‐particle heat transfer in continuous tube flow: Comparison between experimental techniques

Abstract

The liquid-to-particle convective heat transfer coefficient (h fp ) is a critical parameter in the design of safe continuous thermal processes for particulate foods. Three methods of measuring h fp values during continuous tube flow were compared: moving thermocouple, liquid crystal, and relative velocity. A model error analysis of the heat transfer methods (moving thermocouple and liquid crystal) indicated that measurement of the temperature and particle velocity were important sources of error. For the relative velocity method, the measurement of relative velocity, the rheological properties of the carrier medium, and thermal conductivity of the fluid were found to be most important. The liquid crystal method yielded the highest values of all techniques, largely because of the freedom of rotation allowed to particles under test conditions. The moving thermocouple and relative velocity methods yielded results that were in agreement with each other, the principal reason being the restriction of rotation in the former, and neglect of rotation in the latter. The moving thermocouple approach can be used for conservative but realistic estimation of h fp in continuous flow through holding tubes. The relative velocity method does not stand on its own, but can be used to provide a measure of verification for the other methods.

Effects of Particle Diameter and Position on Hydrodynamics around a Confined Sphere

“…This may constrain accurate design of industrially important processes. One important example is in the field of aseptic food processing, where the relatively slow-to-heat food particles are sterilized by heating the carrier fluid inside a holding tube. − In these applications, the kinetic parameter of microbial destruction is highly sensitive to temperature. Variations in heating duration and heating rate of the particle may significantly affect the outlet product sterility.…”

Effects of Particle Blockage and Eccentricity in Location on the Non-Newtonian Fluid Hydrodynamics around a Sphere

“…Assuming these coefficients to be the same as those applicable under unconfined situations and uniform fluid flow may lead to erroneous design and unpredictable outcomes in industrially relevant applications. One example is aseptic food processing where the solid food particle suspended in a holding tube undergoes thermal sterilization. − If the forces acting on the particles are wrongly predicted and the designed holding tube length is longer than required, overprocessing of food particles may lead to a product of unacceptable quality. Additionally, the particles may not be always suspended at the tube center.…”

Effect of Blockage Ratio on Drag and Heat Transfer from a Centrally Located Sphere in Pipe Flow

“…This causes a serious constraint in the process design of industrial applications. One example is aseptic food processing where solid food particle is immersed in a holding tube (Salengke and Sastry, 1996;Balasubramaniam and Sastry, 1996;Ramaswamy et al, 1997). In this application, suspended food particulate is thermally sterilized due to the heating provided by the surrounding carrier fluid.…”