Experimental measurements of bubble convection models in two-phase stratified liquids

Abstract

The surface flow generated by a bubble plume is a technique proposed to collect the surface-floating substances. This has a great importance when handling the oil layer formed during large oil spill accidents due to the need to protect naval systems, rivers, and lakes. The motivation of this research is to broaden the understanding of oil flow in the stratified layer of oil on the free surface. Laboratory experiments have been carried out in order to investigate the multi-dimensional motion of water and oil due to bubbles. The flow structure of bubble-induced convection in a stratified liquid is investigated by using particle imaging velocimetry (PIV) measurements and pathline measurements. It is confirmed by this paper that the flow structure is strongly modulated by the gas flow rate and bubble size. The velocity of the surface flow induced by the bubble plume in the vicinity of the oil-water interface is about 50% larger and stronger than that inside the oil layer. Moreover, the surface flow is particularly rapidly generated in the vicinity of the oil-water interface. The highest kinetic energy (which is 0.012(m/s)2) is generated at a far distance inside the bubble plume and in the vicinity of the oil-water interface. This observation confirms the idea that the bubble plume can indeed generate a strong and wide surface flow over the bubble generation system. The oil layer is easily broken by bubbles, especially with high void fraction and small bubble size and high gas flow rates. The experimental results were compared with the numerical results of our earlier paper. It is confirmed by this paper that the experimental results resemble the numerical results. As a reference, in a thermally stratified liquid, the liquid flow pattern of bubble-induced convection has also been measured by using thermo-sensitive liquid crystal tracer particles in which a color-image processing is combined to measure the temperature field. These results were compared to the immiscible stratified cases.