Experimental Investigation Of Bubble Hydrodynamics Behaviours In Newtonian Fluids

Gas liquid contacting is a common and important operation in process industries. In most cases, the gas liquid contacting is achieved by dispersing the gas into liquid in the form of bubbles. Bubble is the basic element of the gas liquid contacting and mass transfer. Phase interaction force, the key parameter for the numerical simulation of gas liquid two phase flow, is also mainly affected by the bubble hydrodynamic behaviors. To get better understanding of mechanism of gas liquid transfer phenomena, the bubble hydrodynamic behaviors were investigated by using PIV and analyzed theoretically in this studyIn the research of single bubble rising in stagnant liquid, of which the Morton number ranges from3.21×10-11to163and bubble Reynolds number from0.02to1200, the rising velocity of bubble is measured, while velocity and drag coefficient are calculated, respectively. It is found that in low Reynolds number region (Re<350), bubble drag coefficient decreases with the increase of Reynolds number (CD oc Re-0.94), while it increases with Reynolds number in relatively high region (CD∝Re2)(350<Re<1200). The classic Jamialahmadi equation is suitable for low viscosity liquids (2.2×10-4Pa·s<μ<3.1×10-2Pa·s), after being modification, it is extent to be as high as1.5Pa·s. In the section of bubble trajectory in water, it is found that the bubble begins to oscillate as the bubble is larger then1.8mm (spherically equivalent diameter), at which the critical Reynolds number is as high as475. The deformation of bubble could be characterized by its aspect ratio, which is correlated with Reynolds number, Eotvos number and Morton number well (E∝Re0.625Eo-1Mo0.291).In the section of double in-line bubbles interaction, leading and trailing bubble sizes range from4mm to12mm and10mm to20mm, and leading bubble is always smaller than the trailing. There exist two cases of bubbles interaction, including coalescence and conjunction, for which the critical size is DL≈8.7mm and Dr≈12.7mm. To a fixed size leading bubble, its rising velocity increases with the size of trailing bubble, while it is the same as a fixed size trailing bubble, and the velocity increase for each bubble has a relation as follows:△UL∝(DL/DT)-1.637Mo0.159and△UT∝(DL/DT)-1.563Mo-0.071. A triangle-cone model is used to describe the wake shape in investigate trailing bubble drag coefficient. It is shown that the trailing bubble coefficient decreases with the relative distance between bubbles, and is lower than that of a free rising single bubble. Based on the experimental data, it is found CD.T∝Re-2Eo1.452.In high viscosity liquid, there exists a type of conjunct bubble. By comparing the rising velocity of single and conjunct bubbles, it is found there is no obvious difference when these ones have equal size. Moreover, conjunct bubbles rising velocity could be charactered by its drag coefficient and the projected area of leading bubble, which is also the function of bubble equivalent diameter, bubble size ratio and Reynolds. Three models are proposed to calculate the conjunct bubbles velocity, and the projected area diameter is more suitable for the description of bubble velocity than its equivalent diameter. In addition, the mobility of bubble surface is also necessary to be taken into consideration.In the research of bubble breakup in shear flow, due to the limitation of measurement technology, single phase flow and bubble breakup phenomena were investigated by using PIV and high-speed camera respectively. The interaction between shear flow and bubble breackup is analyze by combining the results. The results show that bubble breakup could be divided into three stages, elongation, middle indentation and rupture, which lasts for about30ms totally. The average conditions for a bubble (9.2mm-14.7mm) breakage are0.045m/s(average velocity),0.0025m2/s2(turbulent kinetic energy)及77.5s-1(shear rate). After dividing the bubble size into several regions by step of0.5mm, it is found that turbulent kinetic energy and flow shear rate could be correlated with bubble size well, which are kc∝e-103Dc and γC∝e-41.0Dc, respectively. Bubble deformation at breakup point is also considered by using Capillary number, which shows the Capillary number and aspect ratio for a breaking bubble have relations Ca∝e49.3D and L/a∝(1-e-3.72Ca)-1, while the inclination of a breaking bubble has no significant relation with Capillary number, though it increases with Capillary number totally.