CONVECTIVE HEAT TRANSFER COEFFICIENT FOR CUBIC PARTICLES IN CONTINUOUS TUBE FLOW USING the MOVING THERMOCOUPLE METHOD¹

Abstract

The convective heat transfer coefficient, hfp, between fluid and cubic particles was investigated with respect to flow rate, viscosity, and particle to tube dimension ratio using a moving thermocouple method. This study was conducted for a single particle. the determined values of hfp ranged from 199 W/m2C and 749 W/m2C. Results indicate that an increase in viscosity or dimension ratio decreased hfp values. In contrast, an increase in flow rate increased values of hfp. the effect of particle to tube dimension ratio was the opposite of those in previous studies by this method and appears to be due to differences inflow regime (laminar in this study, as compared to fully developed turbulence in previous work). A dimensionless correlation developed to relate Nusselt number to generalized Reynolds and Prandtl numbers, ratio of particle characteristic length and diameter of the tube, had an r2 value of 0.94.

DETERMINATION of CONVECTIVE HEAT TRANSFER COEFFICIENT BETWEEN FLUID and CUBIC PARTICLES IN CONTINUOUS TUBE FLOW USING NONINVASIVE EXPERIMENTAL TECHNIQUES1

“…For particle to tube size ratio, h, values increased when the particle size decreased (p <0.05). The above observation is similar to the result obtained using moving thermocouple methods (Zitoun and Sastry 1994), but there is an apparent inconsistency with the results obtained by Sastry et al (1990). The principal reason for the difference is the flow regime: laminar in the present instance; fully developed turbulence in the earlier study.…”

“…More recent work from this laboratory (Balasubramaniam and Sastry 1994) has found that under laminar flow conditions, the effect of particle-to-pipe dimension ratio was not clear cut; this was attributed to variation in particle trajectories (which were not controlled). Zitoun and Sastry (1994) determined convective heat transfer coefficients for cubic particles in non-Newtonian carrier fluids in laminar flow using the moving thermocouple approach of Sastry et al (1990). Results indicated increasing heat transfer coefficients with increasing flow rate, decreasing viscosity and decreasing particle-to-tube dimension ratio.…”

“…The differences were attributed to the mixed and highly turbulent flow regime in the earlier study, which resulted in the dominance of "channeling" or "Bernoulli" type effects under turbulent flow. However, the study of Zitoun and Sastry (1994) did not involve control of particle trajectories. A better understanding of trends in h, would be achieved if parameters such as radial location were controlled, dictating the use of suitable noninvasive techniques.…”

Transport phenomena in food engineering: basic concepts and advances

“…That coefficient and data on residence time distribution are necessary to design different processes, such as those in which particles are moving through a heat exchanger and holding tubes sections (as is the case of aseptic processing systems). Different correlations to predict fluid-to-particle heat transfer coefficients (h fp ) for processing of particle foods flowing in tubes have been developed recently to solve this kind of problems (Sastry & Zuritz, 1987;Chandarana, Gavin, & Wheaton, 1990;Zuritz, McCoy, & Sastry, 1990;Mwangi, Datta, & Rizvi, 1992;Balasubramaniam, 1993;Zitoun & Sastry, 1994a, 1994bAstrom & Bark, 1994;Bhamidipati & Singh, 1995;Awuah & Ramaswamy, 1996;Chakrabandhu & Singh, 1998). Zareifard (2000, 2003), and Zareifard and Ramaswamy (2001) developed correlations for experimental data obtained from two techniques allowing particle motion during the heating process: a calorimetric method (CM) in which the particle was free to move and rotate along the length of holding tube, and a particle oscillatory motion method (POMM) in which particle was allowed a controlled movement in an oscillatory fashion.…”

Design of Conservative Simulated Particles for Validation of a Multiphase Aseptic Process

“…Heat penetration measurements for a food particle traveling through an aseptic processing system are difficult and not practical at the present time without restricting the free movement of food particles (Sastry 1986; Lee and Singh 1990; Heldman 1992; Maesmans and others 1994). Due to challenges encountered in measuring the temperature of moving particles in aseptic processing systems, several alternatives have been considered, such as biological validation techniques (Cacase and others 1994), moving thermocouple methods (Sastry 1992; Zitoun and Sastry 1994a), liquid crystal technique (Zitoun and Sastry 1994b), time temperature integrators (Guiavarc'h and others 2002), melting point indicators (Mwangi and others 1993), and relative velocity methods (Balasubramaniam and Sastry 1994).…”