Marangoni effect

About: Marangoni effect is a research topic. Over the lifetime, 5336 publications have been published within this topic receiving 98562 citations. The topic is also known as: Gibbs–Marangoni effect.

Thinning and disturbance growth in liquid films mobilized by continuous surfactant delivery

Abstract: A generalized linear stability analysis is applied to the case of a thin liquid film propelled to spread by a continuous supply of surfactant. The time-dependent base states for the film thickness and surfactant concentration give rise to a nonautonomous system describing disturbance propagation. As a first approximation, the nonautonomous operator is treated as time independent, thereby reducing the system of equations to a standard eigenvalue problem. For the range of parameters investigated, this modal approximation reveals a band of unstable modes corresponding to the growth of transverse, sinusoidal corrugations. A transient growth analysis of the fully time-dependent system, which requires the solution of an initial value problem, also signals the possibility of large disturbance growth. In both cases, significant amplification of infinitesimal disturbances can be traced to the region of the film most rapidly thinned by Marangoni stresses, which is characterized by large interfacial curvature and a sharp variation in shear stress. In contrast to previous models implementing a finite surfactant source that predict asymptotic stability, large transient growth and asymptotic instability are possible for the case of sustained surfactant release.

Microgravity experiments on flame spread of an n-decanedroplet array in a high-pressure environment

Abstract: The flame spread phenomena of an n -decane droplet array in the supercritical pressure range were experimentally investigated in microgravity. Experiments were conducted at presure up to 5.0 MPa, which is over the critical pressure of n -decane. Observations of the flame-spread phenomenon were conducted using OH-radical emission, Schlieren, and back-klit images recorded by a high-speed video camera. The flame-spread rates were calculated on the basis of the time history of the OH-emission images. Im microgravity, the flame-spread rate decreased with increasing pressure, had a minimum at a pressure around half of the critical pressure, and then increased again. It had a maximum at the pressure near the critical pressure and then decreased gradually with pressure. In normal gravity, the flame-spread rate monotonously decreased and there was a pressure limit beyond which flame spread did not occur. Around the critical pressure, a jet-like flow of fuel vapor from an unburned droplet heated by the flame of a burning droplet was observed. The fuel-vapor jet from theside opposite the heating region of the unburned droplet reached another adjoining unburned droplet and then flame propagated along the jet, leading to heating pior to ignition of the unburned droplet. The mechanism of the fuel-vapor jet was examined based on the shear flow near the droplet surface induced by Marangoni convection of the unburned droplet heated non-niformly by the burning deoplet. The droplet internal flow rate was measured in normal gravity and confirmed the existence of Marangoni convection. The internal flow rate increased with pressure and had a maximum near the critical pressure. It was expected that the mechanism responsible for the maximum flame-spread rate near the critical pressure was the enhanced heat and mass transfer caused by the fuel-vapor jet and flame propagation along that jet.

Report on Microgravity Experiments of Dynamic Surface Deformation Effects on Marangoni Instability in High-Prandtl-Number Liquid Bridges

Abstract: This paper reports an overview and some important results of microgravity experiments called Dynamic Surf, which have been conducted on board the International Space Station from 2013 to 2016. The present project mainly focuses on the relations between the Marangoni instability in a high-Prandtl-number (Pr= 67 and 112) liquid bridge and the dynamic free surface deformation (DSD) as well as the interfacial heat transfer. The dynamic free surface deformations of large-scale liquid bridges (say, for diameters greater than 10 mm) are measured with good accuracy by an optical imaging technique. It is found that there are two causes of the dynamic free surface deformation in the present study: the first is the time-dependent flow behavior inside the liquid bridge due to the Marangoni instability, and the second is the external disturbance due to the residual acceleration of gravity, i.e., g-jitter. The axial distributions of DSD along the free surface are measured for several conditions. The critical parameters for the onset of oscillatory Marangoni convection are also measured for various aspect ratios (i.e., relative height to the diameter) of the liquid bridge and various thermal boundary conditions. The characteristics of DSD and the onset conditions of instability are discussed in this paper.