Experimental studies of direct contact heat transfer in a slurry bubble column at high gas temperature of a helium–water–alumina system

Slurry bubble column reactors (SBCRs) that are considered as multiphase reactors, are used in numerous industrial applications due to their inherent advantages. They are characterized by high heat transfer rates per unit volume of the reactor as well as better temperature control. In spite of the constructional simplicity of the Slurry bubble column reactors , the scale up analysis of such reactors is complex, because of the strong influence of hydrodynamic parameters on heat transfer properties. Direct-contact heat transfer in a Slurry bubble column reactor occurs when the heat is transferred between a dispersed gas phase and a primary slurry phase in the absence of a separating wall. It involves a complex phenomenon of bubble formation and gas motion through the liquid layer. Therefore, empirical equations from experimental studies are important to describe the direct contact heat transfer.

In the literature, most of the experimental studies and empirical correlations that were performed on different systems to study the direct contact heat transfer, were limited to air/water systems. There is a lack in studying a slurry bubble column reactor with a high temperature helium gas. This lack motivates the present research, which seeks to fill this gap by investigating experimentally the volumetric heat transfer coefficient and the slurry temperature of a slurry bubble column reactor with direct contact heat transfer. In the experiments, a helium gas at 90^oC is injected through a slurry of water at 22^oC and alumina solid particles. Helium gas is considered as a perfect heat transfer medium, because of its high thermal conductivity and specific heat in addition to its inertness and safe usage. The high thermal conductivity of the helium gas will help in decreasing the thermal resistance of the gas side in the direct contact heat transfer. In the literature, it has been shown that the gas density has a significant impact on heat transfer of bubble columns. Since there is a large difference in densities between helium gas at 90^oC and air at ambient temperature, the use of the previous literature results of air/water systems to predict the volumetric heat transfer coefficient of a slurry bubble column reactor with a high temperature helium gas can be risky.

The other feature that characterizes the experimental work of this paper is that, the reported empirical equations of the volumetric heat transfer coefficient were mainly formulated in terms of thermo physical properties of the gas and slurry. In this paper, a new form of empirical equation for the volumetric heat transfer coefficient was formulated in terms of the bubble column design parameters only, such as the reactor dimensions, superficial gas velocity, and solid concentration.