Sponsor: NASA
Surface-tension-driven flows are of central concern in a microgravity environment because they can be the dominant flows in some processes used in the space environment. The success of these processes is therefore linked to our degree of understanding of the accompanying surface-tension-driven flow. In this project, we consider a thermocapillary flow in a thin film contained in a shallow slot. Asymptotic methods are used to develope a nonlinear equation describing the behavior of the free surface of this film. The equation includes the effects of surface tension, surface-tension gradients, free-surface heat transfer, and viscosity. End effects are modeled by the end boundary conditions. Additional effects that can be included are inertia and the curvature of the film when in a cylindrical geometry. The equation is solved numerically using spectral methods. We use the results to examine the possibility of steady flows and their stability. We also examine the possibility of unsteady flows that may lead to the rupture of the liquid film. These numerical simulations will improve our understanding of how unsteady thermocapillary flows behave in a bounded domain and will help identify the associated instability mechanisms.
Sponsor: NASA
In a micro-gravity environment, there is a need for methods
to control and manipulate small and large masses of fluid in order
to ensure that the associated systems behave properly. In this
project, we investigate one technique for micro-gravity fluid
management. The idea is to impose a temperature gradient on a
rigid surface so as to produce a thermocapillary flow in a liquid
droplet attached to the surface. This flow alters the shape of
the liquid droplet, which it turn can cause the droplet to move
along the surface due to contact-line dynamics. Previous work
has shown the proof of this concept with a two-dimensional droplet.
In the current project, we are extending this work to model a
fully three-dimensional droplet. The initial work involves a thin
droplet and the development of a nonlinear evolution equation
for the free surface using lubrication theory. The equation will
be solved numerically. The results will help us describe the physics
of thermocapillary droplet migration and the extent to which it
can be successfully applied in a real micro-gravity application.
Professors G. Paul Neitzel and Marc K. Smith, in conjunction
with Professors Robert M. Nerem (ME), Athanassios Sambanis (ChE)
and Timothy M. Wick (ChE)
Sponsor: NASA
Bioreactors are vessels in which biological cells may be cultured, to the point that actual tissues may be grown. The fluid-dynamic environment of the bioreactor is crucial to the success of the endeavor. The tissues are fragile and do not survive in high-shear environments, however, convection is necessary both to provide nutrients to the cells and to rid the neighborhood of the cultures of waste products. Consequently, efforts to tailor the flow within the bioreactor to best meet these constraints and requirements may yield enormous benefits. The work associated with this project will seek to characterize the flow within an existing, rotating-wall bioreactor, to examine the response of tissues to varying shear stresses, and, ultimately, to redesign the bioreactor to provide a more hospitable environment for tissue growth.
Thin liquid films are seen in many technologies involving such things as film cooling, coating processes, condensation processes, gas absorption processes, and lubrication of crude oils in pipes. One project in this area involves the characterization of a thin liquid film flowing down a heated, vertical cylinder. A uniform thin film is always unstable and an evolution equation describing the behavior of this instability has been derived. Initial numerical investigations have described the approach of the film to stable traveling waves on the interface. Some experimental work has shown how the film ruptures if the film flow rate is too low. Future work will be involved with both of these areas.
Another project in this area is concerned with the spreading of a surfactant layer over another liquid layer. Here, we must consider the initial spreading to be of a bulk liquid spreading over another bulk liquid. Eventually, the upper liquid becomes a monolayer and the spreading process proceeds by a different path. Our work involves the theoretical characterization of each of these spreading processes, and the numerical solution of the resultant equations.
Go to the Marc Smith's Home Page
Last Modified: October 4, 1996
Contact: marc.smith@me.gatech.edu