Engineering topics

Balasubramaniam, R.

Publications and source records attributed to Balasubramaniam, R..

59 records · Page 4

NASA NTRS1988

Electrohydrodynamic migration of charged droplets in an insulating fluid

The motion of charged, conducting droplets present in an insulating fluid medium is analyzed under the action of an electric field, in microgravity. Previous analyses of this problem have considered the Maxwell stresses as the only driving force. In the present study, arguments from macroscopic thermodynamics and the molecular theory of surface tension are used to show that the surface tension gradients can be induced due to the variation of the electric potential on the interface. In the limit of Reynolds numbers small compared to unity, the terminal velocity of migration of the droplet is calculated under the combined action of the Maxwell stresses and the surface tension gradients. The results show that there are no surface tension gradients (i.e., no electric potential variation at the interface) in a case that is due to the convection of the surface charges, surface tension gradients do exist and tend to reduce the terminal velocity of the droplet. The shape of the droplet altered by the motion was also calculated, when the deformations from the speherical shape are small.

Balasubramaniam, R.↗

NASA NTRS1988

Unsteady thermocapillary migration of bubbles

Upon the introduction of a gas bubble into a liquid possessing a uniform thermal gradient, an unsteady thermo-capillary flow begins. Ultimately, the bubble attains a constant velocity. This theoretical analysis focuses upon the transient period for a bubble in a microgravity environment and is restricted to situations wherein the flow is sufficiently slow such that inertial terms in the Navier-Stokes equation and convective terms in the energy equation may be safely neglected (i.e., both Reynolds and Marangoni numbers are small). The resulting linear equations were solved analytically in the Laplace domain with the Prandtl number of the liquid as a parameter; inversion was accomplished numerically using a standard IMSL routine. In the asymptotic long-time limit, the theory agrees with the steady-state theory of Young, Goldstein, and Block. The theory predicts that more than 90 percent of the terminal steady velocity is achieved when the smallest dimensionless time, i.e., the one based upon the largest time scale-viscous or thermal-equals unity.

Dill, Loren H.↗

NASA NTRS1987

Thermocapillary bubble migration for large Marangoni Numbers

The thermocapillary motion of spherical bubbles present in an unbounded liquid with a linear temperature distribution, when the Reynolds number and the Marangoni number are large is analyzed. Previous calculations of the terminal velocity performed for this parametric range did not take into complete consideration the thermal boundary layer present near the surface of the bubble. A scaling analysis is presented for this problem. The thermal boundary layer is analyzed by an integral method. The resulting terminal velocity is lower than the one previously calculated, though it is of the same order of magnitude.

Balasubramaniam, R.↗

NASA NTRS1987

Simulation of fluid flows during growth of organic crystals in microgravity

Several counter diffusion type crystal growth experiments were conducted in space. Improvements in crystal size and quality are attributed to reduced natural convection in the microgravity environment. One series of experiments called DMOS (Diffusive Mixing of Organic Solutions) was designed and conducted by researchers at the 3M Corporation and flown by NASA on the space shuttle. Since only limited information about the mixing process is available from the space experiments, a series of ground based experiments was conducted to further investigate the fluid dynamics within the DMOS crystal growth cell. Solutions with density differences in the range of 10 to the -7 to 10 to the -4 power g/cc were used to simulate microgravity conditions. The small density differences were obtained by mixing D2O and H2O. Methylene blue dye was used to enhance flow visualization. The extent of mixing was measured photometrically using the 662 nm absorbance peak of the dye. Results indicate that extensive mixing by natural convection can occur even under microgravity conditions. This is qualitatively consistent with results of a simple scaling analysis. Quantitave results are in close agreement with ongoing computational modeling analysis.

Roberts, Gary D.↗

NASA NTRS1987

Simulation of fluid flows during growth of organic crystals in microgravity

The improvements in crystal size and quality obtained in counterdiffusion-type crystal growth experiments in space are sometimes attributed to the reduction of natural convection in microgravity. Attention is presently given to the results of both the Space Shuttle-conducted and terrestrial versions of the Diffusive Mixing of Organic Solution experiments. Extensive mixing by natural convection is noted to occur even under microgravity conditions, in keeping with the results of a simple scaling analysis.

Roberts, Gary D.↗