Thermocapillary convection in a liquid bridge is induced by non-uniform surface tension distribution over the free surface owing to a temperature difference between two cylindrical rods sustaining the liquid bridge. Types of the induced flows were categorized into several regimes mainly according to the suspended particle motion in the bridge and the surface temperature variation. The particle accumulation structure (PAS) has been observed accompanied with the traveling wave oscillation in the liquid bridge. Besides, a feedback control upon nonlinear thermocapillary convections in a half-zone liquid bridge of a high Prandtl number fluid was conducted. The traveling wave, which may emerge in a long liquid bridge, is investigated in comparison with the hydrothermal wave, emerging in a thin liquid layer. The difference and the similarity in the oscillatory flow between long and short liquid bridge are discussed.
This paper presents a technique for measuring two-dimensional dynamic surface deformation (DSD) of liquid bridge with thermocapillary convection by using temporal speckle pattern interferometry (TSPI). The technique includes two parts; one is the determination of multiple reference phases from phase-shifted speckle images and the other is the recovery of DSD-induced phase variations from sequential specklegrams that are correlated with the reference phases. The reference phases are determined by using a temporal speckle phase method (TSPM) incorporating a piezoelectric translator. On the other hand, the phase variations are recovered by using a new algorithm that is modified from the method proposed by Carlsson & Wei (2000). It utilizes neighboring pixel information to calculate the phase change from a pre-determined initial phase to be determined separately. The present modification is done by replacing the use of a single initial phase with that of multiple reference phases so as to minimize the effect of errors in the initial phase as well as in the specklegrams acquired. The present method is shown to be effective for dealing with both large noise in specklegram and error in initial phase. Its performance is verified through both computer simulations and direct comparisons with the data obtained using a different method. The DSD results measured in pulsating mode and in rotating mode in oscillatory thermocapillary convection are reported here. Some new features, such as the propagation direction of DSD wave, are detected in the first from the present measurement.
Studies on the Marangoni flow of molten silicon are reviewed. Marangoni flow of low Pr number fluids, such as molten silicon, have been carried out mainly experimentally from the viewpoint of application. Since, for molten silicon, it is rather difficult to attain small Marangoni number, a partially confined structure has been employed both for experimental and numerical studies. The critical Marangoni number Mac3 is an important criterion from the application viewpoint. Flow instability has been studied experimentally; basic relationship between an aspect ratio and azimuthal wave number is sustained even under the large Marangoni number case.
The experimental study on thermocapillary convection of low Prandtl number fluid was carried out to investigate the transition behavior to oscillatory flow. The half-zone liquid bridge of molten tin was used as a test configuration. It could be experimentally detected that the axisymmetric steady flow changes to three-dimensional steady one with increasing the temperature difference between hot and cold disks. At higher temperature difference, oscillatory transition was also observed. Aspect ratio dependence on critical Marangoni number was made. The experimental result of a first critical Marangoni number agreed very well with numerical one.
Experimental and numerical researches on Marangoni convections in thin layer of low and high Pr number fluids in annular pools are reviewed. First, the Marangoni instability in thin layers of liquids during heat or mass transfer through interface is reviewed very briefly in order to distinguish them from the hydrothermal wave type thermocapillary flow instability. Secondly, hydrothermal wave type instabilities in rectangular liquid pools are reviewed very briefly. Then, observed and numerically reproduced hydrothermal wave type instabilities in annular pool of silicon melt and silicone oil are reviewed and explained in detail.
A round liquid jet issued into an otherwise quiescent gas at a pressure far exceeding the critical pressure of the liquid has a thermodynamic surface state close to a critical mixing condition, yielding a vanishingly small surface tension and a large gas density at the surface. Thus, under microgravity conditions, large-Weber-number instability behaviors can be successfully observed using a near-critical-mixing-surface jet issued at low speed from a nozzle in laminar-flow form. Mechanisms for the excitation of Taylor instability immediately downstream of the nozzle exit and for the shortwavelength disintegration of the liquid jet are explored on the basis of microgravity experiment observations and theoretical considerations, in order to characterize the initiation of capillary instability and the breakup of liquid ligaments into drops involved in turbulent atomization.
This article summarizes research in fluid dynamics instability especially addressing the Marangoni convection problems. In the introductory and following sections, the general information concerning a fluid dynamics and instability is described. In the following section, current status of Marangoni research in liquid bridge configuration are overviewed, while in the last section, the candidate themes of space experiment utilizing the International Space Station (ISS) are introduced and the perspectives in fluid science are remarked.
Moving ‘contact line’ as the boundary line of solid-liquid-gas interface is so familiar phenomenon in a daily lives; such as sliding rain droplet on the window, advancing wine in the glass in drinking it, falling droplet on your body in taking a shower, etc. Such phenomena can be often seen also in industrial situations; coating of the solid surface by a liquid film, extending a dry patch in a liquid film on the heated surface in a heat exchanger, growing bubble and rewetting after the bubble detaching on the solid surface in boiling phenomena, and so on. A large number of experimental and theoretical researches have been conducted upon the moving contact line, and they have indicated that there exists a precursor thin liquid film preceding the advancing bulk liquid film or droplet. The dynamics of the fluid in the vicinity of the contactline region, however, is not understood at all. In the present manuscript, typical phenomena concerning the moving contact line and the preceding works in this field are abstracted, and then the latest topics by the present authors' group are introduced.
Microgravity fluid physics is an important part of the microgravity science for understanding the macroscopic fundamental phenomena in the microgravity environment, and is also the basis of many microgravity engineering and subjects of other fields in microgravity sciences. The main results on the space experiments of fluid physics in China are summarized in the present paper.
Effects of tilted laser angle on absorption-induced spontaneous ignition of PMMA sheet in microgravity are numerically investigated. Laser absorption via MMA vapor (produced by PMMA decomposed reaction) plays a key role to lead spontaneous ignition in this system. Laser exposure angle, total laser power, and laser profile are varied to discuss about the their roles on the ignition. Calculated results show that an ignition delay time is not solely controlled by laser power; imposed laser density on the surface can also be important. Multiple of ‘laser density’ and ‘laser power’ is found to predict the ignition delay time fairly well. This suggests that former one (related to PMMA heat up time) and latter one (related to MMA heat up time) gives equivalent effect on the ignition.