We report measurement of azimuthal velocity as a function of radius near the boundary between a liquid annulus and (a) a rigid freely floating cylinder and (b) an air core contained in a rapidly rotating horizontal cylindrical container. Case (a) agrees with previous theoretical calculations and verifies the method. Case (b) demonstrates (1) that the interface can support stress and (2) that there is a distinct difference in the scale of radial variation in the bulk liquid from that observed in case (a).

Single bubble behavior inside a rotating liquid-filled sphere is studied both experimentally and theoretically. In the limit of small values of the Taylor number, a quasi-static theoretical description of the motion of the bubble is developed. The analytical result thus obtained is compared with experiment and predicts the bubble trajectory as well as its asymptotic location which, in the presence of gravity, is not exactly on the axis of rotation.

A mathematical representation has been developed for the electromagnetic force field, the fluid flow field, the temperature field (and for transport controlled kinetics) in a levitation melted metal droplet. The technique of mutual inductances was employed for the calculation of the electromagnetic force field, while the turbulent Navier-Stokes equations and the turbulent convective transport equations were used to represent the fluid flow field, the temperature field and the concentration field. The governing differential equations, written in spherical coordinates, were solved numerically.

The computed results were found to be in good agreement with measurements reported in the literature, regarding the lifting force and the average temperature of the specimen.

Closed ampoule vapor transport techniques are widely employed for the preparation of single crystals [1–5]. The experimental simplicity of these techniques makes them also attractive for fundamental crystal growth transport studies in reduced gravity environments. However, the underlying transport processes are complex and difficult to quantify.

Although the instability of an initially motionless fluid subjected to a Rayleigh-type acceleration is well known, this type of excitation applied to an initially moving fluid has not been studied previously. We have therefore performed numerical analyses for two-dimensional unsteady thermal convection in circular cylinders under variable low-g conditions associated with space flight. When an acceleration vector is applied parallel to the thermal gradient for a fluid at rest, no convection results for the stable direction, and an instability leads to Rayleigh convection for the opposite direction. However, when the acceleration has a component which is orthogonal to the gradient, convection always results at any Rayleigh number; this is the usual situation during space flight. We therefore study the resultant effect on convection when both types of acceleration are applied, concurrently or sequentially, and when the resultant vector varies in direction with time. Our results indicate that for space flight conditions, the Rayleigh accelerations impose significant, but not dominating, alterations in the established convection even when the Rayleigh number is less than critical.

There are at least two ways that hydrodynamic processes can limit continuous flow electrophoresis. One arises from the sensitivity of the flow to small temperature gradients, especially at low flow rates and power levels. This sensitivity can be suppressed, at least in principle, by providing a carefully tailored, stabilizing temperature gradient in the cooling system that surrounds the flow channel. At higher power levels another limitation arises due to a restructuring of the main flow. This restructuring is caused by buoyancy, which is in turn affected by the electro-osmotic crossflow. Approximate solutions to appropriate partial differential equations have been computed by finite difference methods. One set of results is described here to illustrate the strong coupling between the structure of the main (axial) flow and the electro-osmotic flow.

Continuous flow electrophoresis employs an electric field to separate biological cells suspended in a flowing liquid buffer solution. Good separations based on differences in electrophoretic mobility are obtained only when a unidirectional flow is maintained. The desired flow has a parabolic structure in the narrow dimension of the chamber and is uniform across the width, except near the edges where the no-slip condition prevails. However, because of buoyancy, very small lateral or axial temperature gradients deform the flow significantly. The results of experiments conducted with a specially instrumented chamber show the origin and structure of the buoyancy-driven perturbations. It is found that very small temperature gradients can disturb the flow significantly, as was predicted by earlier theoretical work.

The two phase systems that result when aqueous solutions of dextran and poly(ethylene glycol) (PEG) are mixed above a critical concentration of a few percent provide a useful medium for the separation of biological cell subpopulations via partition between the top, PEG-rich phase and the liquid-liquid phase boundary. Interfacial tensions of such systems have been measured by the rotating drop technique and found to range between 10−1 and 102 μN m−1 . The tension was found to depend on the length of the tie line describing the system on a phase diagram, via a power law relationship which differed depending on the concentration of Na phosphate buffer present. The electrokinetic properties of drops of one phase suspended in the other were studied for a variety of systems. It was found that the droplet electrophoretic mobility increased monotonically with phosphate concentration and drop diameter but exhibited the opposite sign from that anticipated from phosphate partition measurements. It was possible to take advantage of these electrokinetic properties and dramatically enhance the speed of phase separation through application of relatively small electric fields.

Two immiscible liquid phases form when an aqueous mixture of the electrically neutral polymers dextran and polyethylene glycol are equilibrated at sufficient concentrations. Certain supporting electrolytes which contain sulphate, phosphate or citrate ions partition unequally between the phases, and in their presence, electrophoresis of a drop of one phase suspended in the other is observed, with large mobilities. These mobilities depend linearly on the radius of the drop and the direction of the drop's motion is reversed when the disperse phase and the continuous phase are interchanged. When those ions which produce electrophoresis are present the potential Implied by the direction of electrophoresis is opposite to the Donnan potential observed between the two phases. To explain these results, we postulate an electric dipole layer associated with a mixture of oriented polymer molecules at the surface of a drop. In addition, a potential difference between the interiors of the two phases results from the unequal ion distribution. For the idealised model of a surface layer of point dipoles the inner and outer diffuse layers carry net charges equal in magnitude but opposite in sign. The classical theory of electrophoresis due to Henry, Overbeek and Booth is adapted to the motion of an emulsion drop under an electric field when diffuse ionic layers are present inside and outside the drop. Relaxation effects are treated for the case where the two diffuse layer thicknesses are small compared with the drop radius. An expression is obtained for the electrophoretic mobility of a drop which depends linearly on radius and also shows an increase with increase in salt concentration. The theory presented here is related to the work of Levich.

The quasi-static thermocapillary migration of a bubble located inside a drop in free fall is considered for arbitrary axisymmetric temperature fields prescribed on the drop surface. Some results are presented, and an approximation based on the superposition of simpler solutions is discussed.

Our overall objective is the development of a process for large scale purification of biologicals by isoelectric focusing (IEF). Thus, it was important to gain a better understanding of the underlying physical phenomena through mathematical modeling and computer simulation of the process. A mathematical model of the steady state in IEF was developed for an L-component system of ampholytes or monovalent buffers. It is based on the fundamental equations describing the components' dissociation equilibria, mass transport due to diffusion and electromigration, electroneutrality, and the conservation of charge. The model consists of ordinary differential equations coupled to a system of algebraic equations. The validity and usefulness of these simulationshas been confirmed in the formulation of actual buffer mixtures for experimental IEF. This model was recently extended to include the transient evolution to a steady state. Furthermore the new formulation applies to other electrophoretic processes, notably isotachophoresis and zone electrophoresis. As a result, we now have the first general model which predicts the behavior of a given chemical system in a variety of electrophoretic processes.

The potential of space electrophoresis is conditioned by the fact that all electrophoretic techniques require the suppression of gravity-caused convection. Isoelectric focusing (IEF) is a powerful variant of electrophoresis, in which amphoteric substances are separated in a pH gradient according to their isoelectric points. A new apparatus for large scale IEF, utilizing a recycling principle, has been developed. In the ground-based prototype, laminar flow is provided by a series of parallel filter elements. The operation of the apparatus is monitored by an automated array of pH and ultraviolet absorption sensors under control of a desk-top computer. The apparatus has proven to be useful for the purification of a variety of enzymes, snake venom proteins, peptide hormones, and other biologicals, including interferon produced by genetic engineering techniques. In planning for a possible space apparatus, a crucial question regarding electroosmosis needs to be addressed. To solve this problem, simple focusing test modules are planned for inclusion in an early Shuttle flight.

The scientific and technological aspects of processing glasses in a microgravity environment offer considerable challenge and potential. Activities directed to obtaining information relevant to processing materials on earth and eventually processing materials in space for use in space will be considered. The features on the space environment—reduced gravitational forces, vacuum of large capacity, unique radiation conditions, and unlimited dimensions of space—will be discussed, with emphasis directed to the first. The implications of reduced gravitational forces for containerless processing, freedom from deformation, the study and control of weak forces, and the absence of convection and density segregation will be explored. On-going programs concerned with glass processing in space will be reviewed, and additional areas which merit investigation will be considered.

Theory and ground based studies of bubble behavior in a fluid in the presence of a temperature gradient strongly indicate the action of a thermocapillary force which causes the bubbles to move. This'phenomenon been considered in the traditional treatments of glass fining. To demonstrate that the observed motion conformed to theoretical prediction it was necessary to perform the experiment under low gravity conditions. NASA's SPAR program provided an excellent opportunity to do this.

A sodium borate melt containing a specific bubble array was subjected to a well defined temperature gradient for more than 4 minutes. The sample was contained in a platinum/ fused-silica cell which permitted photographic coverage of the experiment. Photographs were taken at one second intervals during the course of the experiment. They clearly show that the bubbles move toward the hot spot on the platinum heater strip. The observed motion is consistent with the theoretical predictions for the temperature gradients parallel and perpendicular to the heater strip.

Experiments on surface tension driven flow in nominally cylindrical columns of a glass melt and silicone oils are described and results are presented. Predictions from an appropriate theoretical model are included. Conclusive proof has been obtained for the dominance of surface tension driven flow in these systems under the conditions of the present investigation.

A preliminary investigation of the effects of a reversible chemical reaction upon the dissolution of an isolated, stationary gas bubble in a glassmelt is presented. The exact governing equations, for the model system, are formulated and discussed. The approximate quasi-steady state version of these equations are solved analytically and bubble dissolution rates are computed. These results are compared with numerical solutions obtained from the finite difference form of the exact governing equations.

Gas bubble motion in a temperature gradient was observed in a sodium borate melt in a reduced gravity rocket experiment under the NASA SPAR program. Large bubbles tended to move faster than smaller ones, as predicted by theory. When the bubbles contacted a heated platinum strip, motion virtually ceased because the melt only imperfectly wets platinum. In some cases bubble diameter increased noticeably with time.

The containerless melting of high-purity multicomponent homogeneous gels and gel-monoliths offers a unique approach to making ultrapure multicomponent optical glasses in the reduced gravity environment of space. Procedures for preparing and characterizing gels and gel-derived glasses in the Na 2o-B2o3-SiO2 system are described. Preparation is based on tLe polymerization reactions of alkoxysilane with trimethyl borate or boric acid and a suitable sodium compound. The chemistry of the gelling process is discussed in terms of process parameters and the gel compositions. The physicochemical nature of gels prepared by three different procedures were found to be significantly different. Infrared absorption spectra indicate finite differences in the molecular structures of the different gels. The melting of the gel powders and the transformation of porous gel-monoliths to transparent “glass” without melting are described.

The effects of retained bound hydroxyl groups on amorphous immiscibility behavior and on the kinetics of phase separation were studied in glasses containing from 10 to 19 percent sodium oxide prepared by the gel process. Differences in behavior as functions of preliminary thermal treatment of the gel precursor and of melting conditions were studied, employing IR spectroscopy, SAXS and WAXD to monitor the variation in glass microstructure. Both the initial gel treatment and the OH concentration in the prepared glasses were found to affect the immiscibility temperatures, and the magnitude of the maximum temperature increase was also a function of the sodium oxide concentration. It is suggested that the variation in thermodynamic behavior may be caused by the structural arrangement attained by the OH groups during the gel condensation process, which in turn affects the extent of hydrogen bonding to nonbridging oxygen ions.