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Fluid thread breakup is the process by which a single mass of fluid breaks into several smaller fluid masses. The process is characterized by the elongation of the fluid mass forming thin, thread-like regions between larger nodules of fluid. The thread-like regions continue to thin until they break, forming individual droplets of fluid. Thread breakup occurs where two fluids or a fluid in a vacuum form a free surface with surface energy. If more surface area is present than the minimum required to contain the volume of fluid, the system has an excess of surface energy. A system not at the minimum energy state will attempt to rearrange so as to move toward the lower energy state, leading to the breakup of the fluid into smaller masses to minimize the system surface energy by reducing the surface area. The exact outcome of the thread breakup process is dependent on the surface tension, viscosity, density, and diameter of the thread undergoing breakup. ==History== The examination of droplet formation has a long history, first traceable to the work of Leonardo da Vinci who wrote: He thus correctly attributed the fall of droplets to gravity, but misinterpreted the mechanism which drives thread breakup. The first correct analysis of fluid thread breakup was determined qualitatively by Young and mathematically by Laplace between 1804 and 1805. They correctly attributed the driver of thread breakup to surface tension properties. Moreover, they also deduced the importance of mean curvature in the creation of excess pressure in the fluid thread. Through their analysis, they showed that surface tension can behave in two ways: an elastic mechanism that can support a hanging droplet and a pressure mechanism due to capillary pressure that promotes thread breakup. Savart followed in 1833 with experimental work, utilizing the stroboscopic technique to quantitatively measure thread breakup. He noted that breakup is a spontaneous process, occurring without an external stimuli. This work allowed him to determine that droplets are produced from a jet flowing from a tank at a distinct rate inversely proportional to the nozzle radius and proportional to pressure in the tank. These observations facilitated Plateau's work that established the relationship between jet breakup and surface energy. Plateau was able to determine the most unstable disturbance wavelength on the fluid thread, which was later revised by Rayleigh to account for jet dynamics. As the surface disturbance becomes large, non-linear theory must be applied. The behavior of jets with large disturbances was examined experimentally by Magnus and Lenard. Their experiments helped to characterize satellite droplets, droplets that are produced in addition to the large main droplet, through the introduction of high speed photography. High speed photography is now the standard method for experimentally analyzing thread breakup. With the advent of greater computational power, numerical simulations have begun to replace experimental efforts as the chief means of understanding fluid breakup. However, difficulty remains in accurately tracking the free surface of many liquids due to its complex behavior. The most success has occurred with fluids of low and high viscosity where the boundary integral method can be employed as the Green's function for both cases is known. Dommermuth and Yue characterized irrotational, inviscid flow by this method as did Schulkes. Youngren and Acrivos considered the behavior of a bubble in a high viscosity liquid. Stone and Leal expanded this initial work to consider the dynamics of individual drops. For fluids of middling viscosity, full simulations using the Navier-Stokes equations are required with methods determining the free surface such as level-set and volume of fluid. The earliest work with full Navier-Stokes simulations was done by Fromm which focused on inkjet technology. Such simulations remain an active area of research. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fluid thread breakup」の詳細全文を読む スポンサード リンク
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