Theoretical And Experimental Investigations On Quasi-laminar Viscous Bubbly Flows

Because bubbly flows are normal phenomena both in nature and industry,it is worth to investigate bubbly flows for science research and practiceapplication. However, few studies on quasi-laminar viscous bubbly flows havebeen developed in the past. So the dissertation presents both theoretical andexperimental investigations on adiabatic incompressible quasi-laminar viscousbubbly flows under conditions of no mass transfer and low void fraction. The experimental study on lift forces on transformable bubbles in shearliquid has been performed. The most possible transverse positions of bubbles(or particles ) in fully developed flows in vertical pipe can be captured by PIV(particles image velocimetry) technology. So the lift forces on bubbles (orparticles) are known, the lift forces and wall forces on bubbles (or particles)are equivalent at the most possible transverse positions. Then the ratios of liftforces on bubbles and particles with the same diameters and conditions havebeen calculated and expressed in empirical formulas. Since the lift forces onparticles have been constructed well, the lift forces on bubbles can be held. The two-fluid model has been derived for quasi-laminar viscous bubblyflows. The basic equations of two-fluid model have been developed byapplying ensemble averaging to the local instantaneous conservation equations.These basic equations can not been calculated until some close laws have beenconstructed. Two of the most important close laws are liquid Reynolds stressand the difference between liquid interface averaged pressure and liquidaveraged pressure, but they are constructed under potential conditions atpresent. So under considering the influence of viscous boundary layer, the newformulas of them are derived by averaging the real liquid velocity field andpressure field around a sphere bubble in cell-ensemble averaging method. Theinterface momentum transfer tensor is constructed by the new formula of liftforce and expressions of other force on bubbles, and other close laws are - II -Abstractprovided. Then the two-fluid model for quasi-laminar viscous bubbly flows hasbeen constructed by these basic equations and close laws. The approximate analytical solutions of the two-fluid model have beenderived for the fully developed quasi-laminar viscous bubbly flows in verticalpipe. Though the approximate analytical solutions are not the real analyticalsolutions and should be calculated by numerical method, they can offer thegenesis of the bubbly flow field more directly. Some quasi-laminar viscous bubbly flows in papers have been predicted bythe approximate analytical solutions of the two-fluid model. It proved that thetwo-fluid model is highly applicable and accurate, since the prediction resultscoincide with the experiment data in most flows.