Mechanical tuning of the evaporation rate of liquid on crossed fibers

We investigate experimentally the drying of a small volume of perfectly wetting liquid on two crossed fibers. We characterize the drying dynamics for the three liquid morphologies that are encountered in this geometry: drop, column and a mixed morphology, in which a drop and a column coexist. For each morphology, we rationalize our findings with theoretical models that capture the drying kinetics. We find that the evaporation rate depends significantly on the liquid morphology and that the drying of liquid column is faster than the evaporation of the drop and the mixed morphology for a given liquid volume. Finally, we illustrate that shearing a network of fibers reduces the angle between them, changes the morphology towards the column state, and so enhances the drying rate of a volatile liquid deposited on it

Development and use of image scanning ellipsometer to study the dynamics of heated thin liquid films. Progress report, July 1, 1989--December 31, 1994

Long-term objective is to determine heat transfer and stability of evaporating ultra-thin films, some of which may form permanent coatings. Goal is to develop and use a microscopic image-processing system (IPS) to measure the film thickness profile; the IPS has two parts: an image analyzing interferometer and an image scanning ellipsometer

Development and use of image scanning ellipsometer to study the dynamics of heated thin liquid films. Final report, July 1, 1989--June 30, 1998

The general objective of this research was to study the characteristics of evaporative phase change in ultra-thin films. The immediate objective was to develop and use microscopic image processing systems (IPS) to measure film thickness profiles. The IPS has two possible configurations: an image analyzing interferometer (IAI) and/or an image scanning ellipsometer (ISE). Both pure liquid films and the formation of sol-gel (xerogels) coatings were studied. An IAI was developed and used to measure the thickness profiles of equilibrium and evaporating liquid films under various conditions. The design and construction of an ISE was also completed and the system was successfully tested by measuring the thickness profile and the refractive index of a non uniform solid film. The profiles of both wetting and partially wetting draining isothermal films were also measured using the ISE. The profiles of the wetting films were analyzed to obtain the dynamics of transport processes in completely wetting thin films. The analysis of the nonwetting profiles continues. TEOS based sol-gels were fabricated in bulk as well as deposited as films on silicon wafers by spin-coating. The authors found that the properties of the final xerogel films are very sensitive to the processing conditions

A Study of the Constrained Vapor Bubble Thermosyphon

The objective of this effort is to better understand the physics of evaporation, condensation, and fluid flow as they affect the heat transfer processes in a constrained vapor bubble heat exchanger (CVBHX). This CVBHX consists of a small enclosed container with a square cross section (inside dimensions. 3 x 3 x 40 mm) partially filled with a liquid. The major portion of the liquid is in the corners, which act as arteries. When a temperature difference is applied to the ends of the CVBHX, evaporation occurs at the hot end and condensation at the cold end resulting in a very effective heat transfer device with great potential in space applications. Liquid is returned by capillary flow in the corners. A complete description of the system and the results obtained to date are given in the papers listed

Aerogel Projects Ongoing in MSFC's Engineering Directorate

When we speak of an aerogel material, we are referring more to process and structure than to a specific substance. Aerogel, considered the lightest solid material, has been made from silica for seventy years. Resorcinol-formaldehyde, organic aerogels have been developed more recently. However, aerogel can be made from almost any type of substance, even lead. Because an aerogel is mostly air (about 99%), the solid substance used will affect the weight very little. The problem with aerogels is their low tensile strength and lack of elasticity. Therefore, the challenge is to find ways to make the stronger or ways to circumvent the strength issue. Organic aerogels have slightly higher strength than base silica aerogels, while the carbonized version has three to five times the break strength of the base aerogel