Donyk T. Heat Transfer and Hydrodynamics in a Tube with Partial Flow Swirl Generator, based on the Cruciform Insert

The thesis is aimed to the experimental and theoretical (computer) studies of heat transfer, pressure drop, local and vortex structures of the turbulent air flow in a round tube with partial swirl generator, based on the cruciform insert. The partial flow swirl is created near the heat transfer surface by means of bendable elements of 0.01 m height, 0.03 m width and angle of their deviation in the wide range. The swirl generator design provides a wide range of the swirl flow angle near the heat transfer surface. This design was protected by the patent of Ukraine for the useful model. In the experiments the swirl flow angle was varied from 15 to 45 degrees. Studies of the in-tube average heat transfer with partial flow swirl have shown that heat transfer augmentation factor varies with a maximum and minimum that is due to specific vortex mixing factor behavor. The pressure drop increases monotonically with a swirl flow angle increase. The summarising of published database have shown that heat transfer intensifiers of a different design having a general mechanism of heat transfer augmentation (flow swirl, flow separation, and vortex mixing) are characterized by the general correlation, based on the Reynolds analogy factor. The in-tube computer simulation with a partial flow swirl has defined some specific features of axial velocity, turbulence and swirl flow angle variations in the near-wall region. Based on the helical line theory, the contribution of individual factors in the heat transfer augmentaion (flow velocity, flow swirl, turbulence, and vortex mixing) has been defined. The results of experimental studies have allowed proposing the new concept of heat transfer intensifier quality coefficient, where the Reynolds analogy factor for the dimpled surface at low Reynolds numbers is used as the basis magnitude. It is shown that for all currently emploted heat transfer intensifiers this coefficient ranges in the slender compass from 0.37 up to 1.0, while for the investigated in this study swirl generators this factor varies from 0.50 to 0.62. The calculation procedure has been developed to predict the in-tube heat transfer and pressure drop with partial flow swirl generator, based on the cruciform insert.