Surface-Tension Devices

Surface-tension devices consist of wicking or grooved surfaces to direct the flow of liquid in boiling and condensing. 

DeBrock, S.C., 1967. Surface tension devices for management of space propulsion system propellants. In SAE Aerospace Systems Conference, Los Angeles, CA, June 27-30. 

DeBrock, S.C., Grove, R.K., Sloma, R.O., Balzer, D.L., Brill, Y., Yankura, GJV., 1971. A survey of current developments in surface tension devices for propellant acquisition. J. Spacecr. Rocket. 8, 83-98. 

The question of time scales has already appeared in this discussion. When a foam is generated, the time scale of surfactant adsorption is very important. If the bubble surfaces are not rapidly covered by surfactant monolayers, bubble rupture is easy, and both foam quantity and stability are poor. The adsorption kinetics can be conveniently studied by dynamic surface tension devices. In these instruments, a fresh surface is created and the surface tension decrease with time due to adsorption can be monitored [6]. Above... 

This is a fairly accurate and convenient method for measuring the surface tension of a liquid-vapor or liquid-liquid interface. The procedure, in its simpli-est form, is to form drops of the liquid at the end of a tube, allowing them to fall into a container until enough have been collected to accurately determine the weight per drop. Recently developed computer-controlled devices track individual drop volumes to = 0.1 p [32]. 

The developed theory of two-phase laminar flow with a distinct interface which is based on a one-dimensional approximation, takes into account the major features of the process the inertia, gravity, surface tension and friction forces and leads to the physically realistic pattern of a laminar flow in a heated micro-channel. This allows one to use the present theory to study the regimes of flow as well as optimizing a cooling system of electronic devices with high power densities. 

However, coalescence of the foam may occur. In aqueous systems, this may be prevented by adding surfactants to lower the surface tension. With organic solvents, this is not as facile. Hence there may be limits to applicability. For unstable gas/liquid dispersions, the micro devices described here may only be used for shortterm contacting. 

The Wilhelmy hanging plate method (13) has been used for many years to measure interfacial and surface tensions, but with the advent of computer data collection and computer control of dynamic test conditions, its utility has been greatly increased. The dynamic version of the Wilhelmy plate device, in which the liquid phases are in motion relative to a solid phase, has been used in several surface chemistry studies not directly related to the oil industry (14- 16). Fleureau and Dupeyrat (17) have used this technique to study the effects of an electric field on the formation of surfactants at oil/water/rock interfaces. The work presented here is concerned with reservoir wettability. 

The n-A curves were measured with a trough equipped with a moving blade and a piezoelectric device (Figure 2). Both the trough (286 mm long and 70 mm wide) and blade were coated with Teflon. The subphase temperature was kept within 0.1 °C by use of a water jacket connected with a thermostated circulation system, and the environmental air temperature was kept at 18 °C. The surface tension was measured with a Wilhelmy plate made of filter paper (25 x 25 x 0.25 mm) using a piezoelectric device. The surface pressure(ji) is defined as ... 

Yarin and Weiss[357] also determined the number and size of secondary droplets, as well as the total ejected mass during splashing. Their experimental observations by means of a computer-aided charge-coupled-device camera and video printer showed that the dependence of the critical impact velocity, at which splashing initiates, on the physical properties (density, viscosity, and surface tension) and the frequency of the droplet train is universal, and the threshold velocity may be estimated by ... 

Finally, as device geometries decrease, spacings between stripes of resist also decrease. With micron and submicron patterns, the surface tension of etch solutions can cause the liquid to bridge the space between two resist stripes. Etching of the underlying film is thereby precluded. 

The various surface forces are seen to be responsible for capillary rise. The lower the surface tension, the lower the height of the column in the capillary. The magnitude of y is determined from the measured value h for a fluid with known pL. The magnitude of h can be measured directly by using a suitable device (e.g., a photograph image). 

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