Experimental study of Influence of depth ratio on convection types of two-layer liquid
- Paper number
IAC-08.A2.4.10
- Author
Prof. Qi KANG, National Microgravity Labrotory, Institute of Mechanick, Chinese Academy of Sciences, China
- Coauthor
Dr. Lujun LI, National Microgravity Laboratory/CAS, China
- Coauthor
Prof. Li DUAN, National Microgravity Labrotory, Institute of Mechanick, Chinese Academy of Sciences, China
- Coauthor
Dr. Liang HU, Institute of Mechanics, Chinese Academy of Sciences, China
- Year
2008
- Abstract
In this paper, the Bénard-Marangoni convections of two-layer fluid heated from below are investigated experimentally. The flows are visualized from side with PIV and structure of velocity fields near onset of convection are observed while the depth ratio varies in a wide range. It is well known that two different mechanisms are responsible for the appearance of the cellular convection when the temperature difference across the liquid layer is above a threshold. They are buoyancy (Rayleigh-Bénard convection) that dominates in relatively thick layers, and interfacial tension (Marangoni convection) that dominates in very thin layers. In some cases both mechanisms are active, which is referred to as the Bénard-Marangoni convection. Buoyancy effect and interfacial tension effect are characterized separately by the Rayleigh number Ra and Marangoni number Ma. The relative important of the two effects is characterized by Bond number Bo which is independent of the temperature difference. Generally, if Bo>1, the buoyancy effect is more important; however, if Bo<1, the interfacial tension effect is more important. The experiments are conducted in a rectangle cavity with the transparent sidewalls and top lid. The horizontal section of the cell is 100mm×40mm. Fluorinert Electronic liquid FC70 and the silicon oil KF96-10CS are chosen. The interfacial tension is assumed to decrease linearly with temperature at the interface and the temperature coefficient of interfacial tension ? is -4.46x10-5N/(mK). The high resolution velocity fields are obtained through processing the particle images with the adaptive and cross correlation method of PIV. In our experiments, the total depth of liquid layer h keeps constant. As the depth ratio hr of two liquid layer varies within 0.25 6.35, convective construction near onset of convection are observed. Comparisons with the Rayleigh-Bénard convection of two-layer fluid reveal the influence of interface tension on the Bénard-Marangoni convection of the two-layer fluid. In term of the local Bond number, convective patterns may very well be explained. Some new patterns are observed in our experiments. One detailed classification is suggested by comparing the motion construction and intensities in both layers at same time. The relationship between the dimensionless wave number and the Bond number is analyzed. Finally, the five types of convection construction are identified, which are caused by the competition of the flow in the bottom and top layers influenced greatly by the ratio of Rayleigh number of two liquid layer Rar and local Bond number.
- Abstract document
- Manuscript document
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