Heat Transfer at the Bottom of a Cylindrical Vessel Impinged by a Swirling Flow from an Impeller in a Draft Tube

Heat transfer at the bottom of a cylindrical vessel impinged by a flow with tangential velocity component generated by an axial-flow impeller in a draft tube was measured using the electrodiffusion experimental method. Local values of the Nusselt numbers along the radial coordinate of the heat transfer surface and corresponding mean values are presented for relatively small distances of the draft tube from the impinged surface (0.25 <= h /d <= 1). Such small distances are typical for mixing of liquids, which ensures good homogenization and increases the intensity of heat and mass transfer in many industrial operations. Results are compared with literature data for unconfined impinging jets with no tangential velocity components. The additional tangential velocity component generated by the rotating impeller significantly influences the hydrodynamics of the impinging jet and decreases the heat transfer intensity in the case of small distances from the impinged surface. A correlation describing the mean Nusselt number at the vessel bottom is proposed. It can be used in a design of a real industrial piece of equipment with heat transfer situated at the bottom.