Heat transfer from a cylindrical probe immersed in a three-phase slurry bubble column

Abstract

Studies conducted on heat transfer and hydrodynamics in a slurry bubble column containing an air-water-magnetite system are described and discussed. In particular, the heat transfer coefficients between a 19 mm heat transfer probe and surrounding two- and three-phase dispersions and the air holdup were measured as functions of air velocity. Magnetite powders of average diameters 35.7, 49, 58, 69, 90.5, 115.5 and 137.5 μm, and powder concentrations up to 30 wt.% in the slurry were employed to investigate the dependence of air holdup and heat transfer coefficient on air velocity, particle diameter and solids concentration in the slurry at 308 K. The experimental results are compared with the predictions of several of the available correlations and models. The gas holdup in the three-phase system is found to be only slightly smaller than that in the corresponding two-phase system, and there is only a weak dependence on particle diameter and slurry concentration. The correlations given by Reilly et al. and Smith et al. appear to be reasonable in giving the upper and lower bounds respectively for the gas holdup in three-phase systems. The heat transfer coefficient for the three-phase system is slightly greater than that for the corresponding two-phase system, and there is only a weak dependence on particle diameter and slurry concentration. None of the available correlations and model expressions are considered adequate for representing the heat transfer data, but for approximate estimations, those given by Deckwer et al. and Kim et al. may be employed; these respectively give overestimates and underestimates of the data.