Sudhir K. Sastry

Effect of fluid viscosity on the ohmic heating rate of solid-liquid mixtures

The effect of fluid viscosity on the ohmic heating rates of fluid-particle mixtures was investigated. Fluids of identical electrical conductivity but different viscosity were used with identical amounts of solid particles (of electrical conductivity lower than the fluid) and heated ohmically in batch (static and vibrating), and continuous flow heaters. In the static ohmic heater, the heating rate of the fluid and particles was found to be comparable for the different fluids. However, in the vibrating ohmic heater, the heating rate of fluid and particles was found to increase with increasing fluid viscosity. In the continuous flow ohmic heater, the mixture with the higher viscosity fluid heated faster than that with the lower viscosity fluid. The important implication is that poor interphase convective heat transfer may actually contribute to accelerated overall heating, since the more (electrically) conductive phase does not lose heat readily to the less (electrically) conductive phase, and consequently heats rapidly, transferring heat to the other phase by larger temperature differences.

Residence time distribution of cylindrical particles in a curved section of a holding tube: the effect of particle concentration and bend radius of curvature☆

Abstract The residence time and the residence time distribution (RTD) of model food particles (cylindrical, diameter and length = 0.02 m, density = 1130 kg/m 3 ) in the curved section of a transparent holding tube have been investigated. Variables included in the study were particle concentration (20%, 30% and 40%) and bend radius of curvature (0.089, 0.22 and 0.28 m). The results show that the means of the normalized residence time tend to increase as either particle concentration or bend radius of curvature increased. However, there was no clear tendency of the effect of the experimental variables on the standard deviation of the normalized residence time. Empirical correlations between the means and the standard deviations of the normalized residence time and particle Froude number, particle concentration, and the ratio of bend radius of curvature to tube diameter are presented.