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NASA NTRS1996

Surface Tension Driven Convection Experiment-2 (STDCE-2

The surface tension driven convection experiment-2 (STDCE-2) was conducted onboard the U.S. Microgravity Laboratory (USML)-2 Spacelab which was launched on October 20, 1995. The main objectives of the experiment was to study oscillatory thermocapillary flows in microgravity. Thermocapillary flows were generated in cylindrical test chambers filled with 2 centistokes silicone oil. Six modules were used to study three different chamber diameters and two different heating modes. Tests with both flat and curved free surfaces were conducted. The flow field was studied by flow visualization and an infrared imaging system recorded the oil free-surface temperature. An optical (Ronchi) system was used to measure the oil free-surface deformation and motions. A total of 55 tests were conducted and oscillations were found in most of them. The data are being analyzed.

Ostrach, Simon↗

NASA NTRS2001

Wetting Angle and Surface Tension of Germanium Melts on Different Substrate Materials

The sessile drop technique has been used to measure the wetting angle and the surface tension of molten germanium (Ge) on various substrate materials. Sapphire, fused silica, glassy carbon, graphite, SiC, carbon-based aerogel, pyrolytic boron nitride (pBN), AlN, Si3N4, and CVD diamond were used as substrate materials. In addition, the effects of different cleaning procedures and surface treatments on the wetting behavior were investigated. The highest wetting angles with values around 170 deg. were found for pBN substrates under active vacuum or with a slight overpressure of 5N Argon or forming gas (2% Hydrogen in 5N Argon). The measurement of the surface tension and its temperature dependence for Ge under a forming gas atmosphere resulted in gamma(T) = 591 - 0.077 (T-T(sub m).

Kaiser, N.↗

NASA NTRS1988

Acoustic measurement of the surface tension of levitated drops

The measurement of the frequency of the fundamental mode of shape oscillation of acoustically levitated drops has been carried out to determine the surface tension of the drop material. Sound fields of about 20 kHz in frequency allow the suspension of drops a few millimeters in size, as well as the necessary drive for oscillations. The surface tension of water, hexadecane, silicone oil, and aqueous solutions of glycerin levitated in air has been measured, and the results have been compared with those obtained with standard ring tensiometry. The two sets of data are in good agreement, the largest discrepancy being about 10 percent. Uncertainties in the effects of the nonspherical static shape of drops levitated in the earth's gravitational field and the rotation state of the sample are the major contributors to the experimental error. A decrease of the resonance frequency of the fundamental mode indicates a soft nonlinearity as the oscillation amplitude increases.

Trinh, E. H.↗

NASA NTRS1987

Calculation of the surface tension of liquid metals using a one-component-plasma reference system

The one-component-plasma (OCP) model is used as a reference system instead of the traditional hard-sphere fluid to calculate the liquid-vapor interfacial surface tension of liquid metals within the density functional formalism. The calculated surface tensions of the alkali metals are in excellent agreement with experiment. For the polyvalent metal Al, the result obtained is larger than experimental measurements. It is concluded that the OCP system is not suitable to describe the liquid-vapor phase transition in simple metals which have a nominal plasma parameter larger than the usual freezing value of about 178. The calculated interfacial widths in all cases are narrower than the expected experimental values.

Zeng, X. C.↗

NASA NTRS1992

Stability analysis of surface tension effects on a double-diffusive layer

The linear stability characteristics of a fluid layer with simultaneous temperature and concentration gradients in a reduced gravity field are examined. The surface tension of the fluid is assumed to be a linear function of temperature and concentration. It is concluded that a small amount of gravity may damp out oscillatory instability or may alter its dynamics so that instability appears as steady convection. The onset of salt-finger instability may be in the overstable mode due to the surface tension method. The Lewis and Prandtl numbers of the material have a strong influence on the stability boundaries and onset characteristics of the system.

Chen, C. F.↗

NASA NTRS2000

Rotating Molten Metallic Drops and Related Phenomena: A New Approach to the Surface Tension Measurement

Molten aluminum and tin drops were levitated in a high vacuum by controlled electric fields, and they were systematically rotated by applying by a rotating magnetic field. When the evolution of the drop shape was measured as a function of rotation frequency, it agreed quantitatively well with the Brown and Scriven's theoretical prediction. The normalized rotation frequencies at the bifurcation point agreed with the predicted value 0.559, within 2%. An anomalous phenomenon which totally deviated from the prediction was observed in rotating molten tin drops when they were kept in a high rotation rate for several hours. No anomaly was observed in aluminum drops when they underwent similar condition. It was speculated that under the strong centrifugal force in the drop the tin isotopes must be separating. Since Al-27 is essentially the only naturally abundant isotope in the aluminum drops, the same anomaly is not expected. Based on the shape deformation of a rotating drop, an alternate approach to the surface tension measurement was verified. This new surface tension measurement technique was applied to a glassforming alloy, Zr(41.2)Ti(13.8)Cu(12.5)Ni(10.0)Be(22.5) in its highly viscous states. Also demonstrated in the paper was a use of a molten aluminum drop to verify the Busse's prediction of the influence of the drop rotation on the drop oscillation frequency.

Rhim, Won-Kyu↗

NASA NTRS1988

Surface tension driven convection experiment

Thermocapillary flow is driven by a thermally induced surface tension variation along a liquid free surface. In the Earth-gravity environment such flows are usually overshadowed by buoyancy driven flows, but at reduced gravity conditions their influence could be significant. A comprehensive theoretical and experimental research program was stated 12 years ago and is still being continued. Past work done at Case Western Reserve University as well as work done by others is reviewed. The justification for low-gravity experiments is presented.

Ostrach, Simon↗

NASA NTRS1989

Surface tension measurements of aqueous ammonium chloride (NH4Cl) in air

Aqueous NH4Cl's solidification is often used to model metal alloy solidification processes. The present determinations of the magnitude of the variation of aqueous NH4Cl's surface tension as a function of both temperature and solutal concentration were conducted at 3, 24, and 40 C over the 72-100 wt pct water solutal range. In general, the surface tension increases 0.31 dyn/cm per percent decrease in wt pct of water, and decreases 0.13 dyn/cm for each increase in deg C. Attention is given to the experimental apparatus employed.

Lowry, S. A.↗

NASA NTRS1976

Surface-tension-induced convection experiment MA-041

In the absence of gravity, stirring in a liquid is suppressed because of density differences caused by thermal or compositional gradients. However, other mechanisms resulting in natural convection in a microgravity environment exist. One of the most important mechanisms for liquid metals is surface tension driven convection, which becomes predominant in the low gravity environment. In this case, surface tension differences caused by compositional or temperature gradients have been demonstrated to cause stirring in liquids during experiments performed onboard Skylab. Compositional gradients were created by adding a soap solution to a large water globule, which caused vigorous fluid motion for some moments after the addition.

Reed, R. E.↗

NASA NTRS1984

The effect of anisotropic crystal-melt surface tension on grain boundary groove morphology

The shape of a stationary solid-liquid interface in a temperature gradient near a grain boundary in a pure material is calculated for anisotropic crystal-melt surface tension and equal thermal conductivities of crystal and melt. Results are compared with those for the well-known problem of the two-dimensional equilibrium shape of a crystal. For small anisotropy, the resulting interface shapes have continuously turning tangents but differ in detail from the grain boundary groove shapes that have been calculated for isotropic surface tension. For larger anisotropy, the interface shapes have discontinuities in slope as a result of missing orientations.

Voorhees, P. W.↗

NASA NTRS1988

Fluoride glass: Crystallization, surface tension

Fluoride glass was levitated acoustically in the ACES apparatus on STS-11, and the recovered sample had a different microstructure from samples cooled in a container. Further experiments on levitated samples of fluoride glass are proposed. These include nucleation, crystallization, melting observations, measurement of surface tension of molten glass, and observation of bubbles in the glass. Ground experiments are required on sample preparation, outgassing, and surface reactions. The results should help in the development and evaluation of containerless processing, especially of glass, in the development of a contaminent-free method of measuring surface tensions of melts, in extending knowledge of gas and bubble behavior in fluoride glasses, and in increasing insight into the processing and properties of fluoride glasses.

Doremus, R. H.↗

NASA NTRS1988

Effect of surface tension anisotropy on cellular morphologies

A three-dimensional weakly nonlinear analysis for conditions near the onset of instability at the crystal-melt interface was carried out to second order, taking into account the effects of latent heat generation and surface-tension anisotropy of the crystal-melt interface; particular consideration was given to the growth of a cubic crystal in the 001-, 011-, and 111-line directions. Numerical calculations by McFadden et al. (1987), performed for an aluminum-chromium alloy with the assumption of a linear temperature field and an isotropic surface tension, showed that only hexagonal nodes (and not hexagonal cells) occurred near the onset of instability. The results of the present analysis indicate that the nonlinear temperature field (which occurs when thermal conductivities of the crystal and the melt are different and/or the latent heat effects are not negligible) can modify this result and, for certain alloys and processing conditions, can cause the occurrence of hexagonal cells near the onset of instability.

Mcfadden, G. B.↗

NASA NTRS1994

A Quasi-Containerless Pendant Drop Method for Surface Tension Measurements of Molten Metals and Alloys

A quasi-containerless pendant drop method for measuring the surface tension of molten metals and alloys is being developed. The technique involves melting the end of a high-purity metal rod by bombardment with an electron beam to form a pendant drop under ultra-high vacuum conditions to minimize surface contamination.

surface tension thermophysical property↗

NASA NTRS1994

Surface Tension Driven Convection Experiment (STDCE)

Results are reported of the Surface Tension Driven Convection Experiment (STDCE) aboard the USML-1 (first United States Microgravity Laboratory) Spacelab which was launched on June 25, 1992. In the experiment 10 cSt silicone oil was placed in an open circular container which was 10 cm wide by 5 cm deep. The fluid was heated either by a cylindrical heater (1.11 cm dia.) located along the container centerline or by a CO2 laser beam to induce thermocapillary flow. The flow field was studied by flow visualization. Several thermistor probes were placed in the fluid to measure the temperature distribution. The temperature distribution along the liquid free surface was measured by an infrared imager. Tests were conducted over a range of heating powers, laser beam diameters, and free surface shapes. In conjunction with the experiments an extensive numerical modeling of the flow was conducted. In this paper some results of the velocity and temperature measurements with flat and curved free surfaces are presented and they are shown to agree well with the numerical predictions.

Ostrach, Simon↗

NASA NTRS1990

Surface tension and viscosity from damped free oscillations of viscous droplets

Damped oscillations of a viscous droplet in vacuum or in an inert gas of negligible density are considered. The dependence of the complex decay factor on the properties of the liquid is investigated for the first time, and numerical results are compared with earlier studies for special cases. A new method is developed to determine both surface tension and viscosity from a single experiment in which the damping rate and frequency of oscillations are measured. The procedure to determine surface tension and viscosity from oscillating levitated liquids is outlined, and results presented for various modes of shape oscillations.

Suryanarayana, P. V. R.↗

NASA NTRS1988

Hardware development for the surface tension driven convection experiment aboard the USML-1 spacelab mission

The Surface Tension Driven Convection Experiment is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for March 1992. Hardware is under development to establish the experimental conditions and perform the specified measurements, for both ground based research and the flight experiment in a Spacelab single rack. Major development areas include an infrared thermal imaging system for surface temperature measurement, a CO2 laser and control system for surface heating, and for flow visualization, a He-Ne laser and optical system in conjunction with an intensified video camera. For ground based work the components of each system were purchased or designed, and tested individually. The three systems will be interfaced with the balance of the experimental hardware and will constitute a working engineering model. A description of the three systems and examples of the component performance is given along with the plans for the development of flight hardware.

Pline, A. D.↗

NASA NTRS1989

Hardware development for the Surface Tension Driven Convection Experiment aboard the USML-1 Spacelab mission

Pline, A. D.↗

NASA NTRS1960

The Surface-Tension Method of Visually Inspecting Honeycomb-Core Sandwich Plates

When one face of a metal-honeycomb-core sandwich plate is heated or cooled relative to the other, heat transfer through the core causes the temperature on each face at the lines of contact with the core to be slightly different from that on the rest of the face. If a thin liquid film is applied to the face, the variation of surface tension with temperature causes the liquid to move from warmer to cooler areas and thus to develop a pattern corresponding to the temperature pattern on the face. Irregularities in the pattern identify the locations where the core is not adequately bonded to the face sheet. The pattern is easily observed when a fluorescent liquid is used and illumination is by means of ultraviolet light. Observation in ordinary light is also possible when a very deeply colored liquid is used. A method based on the use of a thermographic phosphor to observe the temperature pattern was found to be less sensitive than the surface-tension method. A sublimation method was found to be not only less sensitive but also far more troublesome.

Katzoff, Samuel↗