Heat transfer enhancement by multilobe vortex generators: Effects of lore parameters

A three-dimensional computational method is developed to study the flow and heat transfer in a circular tube with a multilobe vortex generator inserte d. Governing equations are discretized by the finite volume technique. The irregular lobe geometry is treated using curvilinear nonstaggered grids. Ex amination of the flow field reveals that the radial and counterradial flows induced inside and outside the lobe are forced to form axial vortices down stream of the vortex generator Because of the transport of the high-speed, low-temperature core flow toward the tube wad by the vortex, heat transfer is enhanced. Also because of the vortex flow, the high-temperature wall flo w is carried away from the wall to mix with the low-temperature core flow. Consequently, very effective augmentation in the heat transfer and mixing o f flow temperature results. It is shown also that since the slope of the lo be is increased by enlarging the lobe penetration, reducing the lobe length , and making a concave contour geometry, the circulation, representing the strength of the axial vortex induced by the lobe, is promoted, leading to h igher heat transfer and flow mixing By increasing the lobe number both the circulation and Nusselt number (Nu) decrease because of the narrowed lobe p assage.