Research Interests: Computer Science, Image Processing, Crystal Growth, Process Control, Adaptive Control, and 9 moreControl system, Artificial Intelligent, Knowledge base, Pole placement, Temperature Control, Liquid-liquid and liquid-solid interface, Multiple-Input Single-Output, Measurement System, and imaging system
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We investigate the effects of convection on physical vapor transport of zinc-telluride by dissociative sublimation computationally and experimentally. We show by solving the coupled set of conservation equations for the corresponding... more
We investigate the effects of convection on physical vapor transport of zinc-telluride by dissociative sublimation computationally and experimentally. We show by solving the coupled set of conservation equations for the corresponding experimental conditions that the flow field is advective-diffusive. This result proves that the traditional approach of calculating the mass flux assuming one-dimensional (1D) flow for low vapor pressure systems is indeed correct. The limit of low Grashof numbers Gr → 0 yields identical results to the 1D case. This implies that for the model considered, a microgravity condition would not affect the transport.
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Effects of convective mixing on the concentration homogeneity of the crystal has been demonstrated. Insitu observations of the solid liquid interface shape during crystal growth are presented which can be used to optimize the dopant... more
Effects of convective mixing on the concentration homogeneity of the crystal has been demonstrated. Insitu observations of the solid liquid interface shape during crystal growth are presented which can be used to optimize the dopant distribution. Observations of the interface during growth are discussed varying the parameters in a controlled manner to minimize the thermosolutal effects. It has been observed that beyond a critical velocity for the particular dopant level, the interface shape changes. The change in the interface shape can be related to the fluid flow in the melt. Two different instability regions, namely convective and morphological are addressed. Experimentally observed result are compared with the existing convecto-diffusive theories.
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ABSTRACT Experiments were performed in controlled conditions to understand both morphological and convective instabilities and results were compared with the theoretical calculations. The sharp contrast between the solid (yellow) and the... more
ABSTRACT Experiments were performed in controlled conditions to understand both morphological and convective instabilities and results were compared with the theoretical calculations. The sharp contrast between the solid (yellow) and the liquid (bright red) phases makes this transparent lead bromide a very suitable material for such an investigation. Crystals doped with 5000 ppm silver bromide were grown. The experimental observations agree with the preliminary results of the numerical prediction. Further, toroidal instabilities resulting from double diffusive convection were observed during crystal growth. Crystals for these interfacial observations were grown in a two zone vertical Bridgman furnace. The acoustic properties were better in doped rather than undoped crystals. Crystals were characterized by x-ray rocking curves and contour scans. Crystals grown at lower Rayleigh numbers showed better quality than crystals grown at higher Rayleigh numbers.
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ABSTRACT A comparative study of thermosolutal convection was carried out by growing lead bromide by silver bromide and studied the transparent Bridgeman furnace. We doped the high purity lead bromide by silver bromide and studied the... more
ABSTRACT A comparative study of thermosolutal convection was carried out by growing lead bromide by silver bromide and studied the transparent Bridgeman furnace. We doped the high purity lead bromide by silver bromide and studied the microsegregation of silver in the matrix of the crystal. Theories based on two extremes: complete diffusive or convective transport did not agree with the experimental data. X-ray rocking curves and contour scans showed that increasing solutal convection deteriorated the crystal quality.
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... CRYSTAL GROWTH Direct observations of interface instabilities NB Singh a,*, SS Mani a, JDAdam a SR Coriell b, ME Glicksman c 9 WMB Duval d, GJ Santoro d9 R. DeWitt d Westinghouse Science & Technology Center, 1310... more
... CRYSTAL GROWTH Direct observations of interface instabilities NB Singh a,*, SS Mani a, JDAdam a SR Coriell b, ME Glicksman c 9 WMB Duval d, GJ Santoro d9 R. DeWitt d Westinghouse Science & Technology Center, 1310 ... [2] SR Coriell and GB McFadden, in: Handbook ...
Research Interests: Chemistry, Convection, Crystal Growth, X Rays, Impurity, and 3 moreCrystal, Single Crystal, and Bromide
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ABSTRACT The improvement in the optical quality of mercurous halide crystals is described. Optical quality was evaluated by studying optical distortion, birefringence interferograms, and laser scattering characteristics; the parameters... more
ABSTRACT The improvement in the optical quality of mercurous halide crystals is described. Optical quality was evaluated by studying optical distortion, birefringence interferograms, and laser scattering characteristics; the parameters which are crucial for practical devices. Mercurous chloride and mercurous bromide crystals showed acoustic attenuation constants of 8 and 11.8 dBμs−1 GHz−2 for cm size crystals. The acoustic attenuation of mercurous iodide was very large and varied significantly because of inhomo-geneities in the matrices of cm size crystals.
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... [5] NB Singh, M. Gottlieb, T. Henningsen, R. Hopkins, R. Mazelsky, ME Glicksman, SR Coriell, WMB Duval and GJ Santoro, J. Crystal Growth 123 (1992) 227. [6] NB Singh, unpublished results. References. 1. NB Singh and ME Glicksman... more
... [5] NB Singh, M. Gottlieb, T. Henningsen, R. Hopkins, R. Mazelsky, ME Glicksman, SR Coriell, WMB Duval and GJ Santoro, J. Crystal Growth 123 (1992) 227. [6] NB Singh, unpublished results. References. 1. NB Singh and ME Glicksman Mater. Letters 5 (1987), p. 453. ...
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The microgravity environment offers the potential to measure the binary diffusion coefficients in liquids without the masking effects introduced by buoyancy-induced flows due to Earth s gravity. However, the background g-jitter... more
The microgravity environment offers the potential to measure the binary diffusion coefficients in liquids without the masking effects introduced by buoyancy-induced flows due to Earth s gravity. However, the background g-jitter (vibrations from the shuttle, onboard machinery, and crew) normally encountered in many shuttle experiments may alter the benefits of the microgravity environment and introduce vibrations that could offset its intrinsic advantages. An experiment during STS-85 (August 1997) used the Microgravity Vibration Isolation Mount (MIM) to isolate and introduce controlled vibrations to two miscible liquids inside a cavity to study the effects of g-jitter on liquid diffusion. Diffusion in a nonhomogeneous liquid system is caused by a nonequilibrium condition that results in the transport of mass (dispersion of the different kinds of liquid molecules) to approach equilibrium. The dynamic state of the system tends toward equilibrium such that the system becomes homogeneous...
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Measurements of the vibration environment on the Russian Mir space station and the US Space Shuttle are compared to the vibration levels predicted for the International Space Station (ISS) and to the vibration levels specified for... more
Measurements of the vibration environment on the Russian Mir space station and the US Space Shuttle are compared to the vibration levels predicted for the International Space Station (ISS) and to the vibration levels specified for isolated payload racks on the ISS. The vibration levels on the Mir and Space Shuttle are generally lower than the levels specified in the
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ABSTRACT The ratio of liquid and solid thermal conductivities was determined for lead bromide by measuring the temperature of solid and liquid under the steady-state conditions. The liquid thermal conductivity was determined to be... more
ABSTRACT The ratio of liquid and solid thermal conductivities was determined for lead bromide by measuring the temperature of solid and liquid under the steady-state conditions. The liquid thermal conductivity was determined to be 10.5×10−4Cal/Kscm, a value 1.65 times higher than that reported for the solid.
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... San Diego, Cal., Paper # 1557-35. 3. Bachman KJ., Kirsh HJ, "Programmed Czochralski Growth of Metals" Journal of Crystal Growth, Vol. 7 p.290-295, 1970. ... 23-25, 1991. Page 14. 15 7. Grimson,WilliamEric Leifur,... more
... San Diego, Cal., Paper # 1557-35. 3. Bachman KJ., Kirsh HJ, "Programmed Czochralski Growth of Metals" Journal of Crystal Growth, Vol. 7 p.290-295, 1970. ... 23-25, 1991. Page 14. 15 7. Grimson,WilliamEric Leifur, "FromImagesTo Surfaces",TheMIT Press,1981. ...
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ABSTRACT The local bifurcation of the flow field, during physical vapor transport for a parametric range of experimental interest, shows that its dynamical state ranges from steady to aperiodic. Comparison of computationally predicted... more
ABSTRACT The local bifurcation of the flow field, during physical vapor transport for a parametric range of experimental interest, shows that its dynamical state ranges from steady to aperiodic. Comparison of computationally predicted velocity profiles with laser doppler velocimetry measurements shows reasonable agreement in both magnitude and planform. Correlation of experimentally measured crystal quality with the predicted dynamical state of the flow field shows a degradation of quality with an increase in Rayleigh number. The global bifurcation of the flow field corresponding to low crystal quality indicates the presence of a traveling wave for Ra = 1.09 x 10(exp 5). For this Rayleigh number threshold a chaotic transport state occurs. However, a microgravity environment for this case effectively stabilizes the flow to diffusive-advective and provides the setting to grow crystals with optimal quality.
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Experimental measurements of pressure drop have been made for forced-convection evaporation and condensation of oil-refrigerant (R-12) mixtures inside a horizontal tube. Data were compared to a wide range of frictional pressure drop and... more
Experimental measurements of pressure drop have been made for forced-convection evaporation and condensation of oil-refrigerant (R-12) mixtures inside a horizontal tube. Data were compared to a wide range of frictional pressure drop and void fraction relationships. The best representations for the oil-free data were then modified to better correlate both oil-free and oil-refrigerant results. For condensation, a modification of the prediction given by the Lockhart-Martinelli relation for frictional pressure drop and the homogeneous void fraction model is presented. For evaporation, the prediction given by the Dukler II frictional pressure-drop correlation and the homogeneous void fraction is modified. These relationships predict the pressure drop for 85% of the data to within +- 35%. The added oil increased the pressure drop 2% to 6% for condensation and 63% to 86% for evaporation.
Research Interests: Thermodynamics, Analytical Chemistry, Mass Transfer, Energy Conservation, Heat Transfer, and 13 moreHeat Exchanger, Mathematical Model, Phase Transformation, Pressure Drop, Energy System, Condensation, Energy Transfer, Forced Convection, Experimental Measurement, Physical Properties, Refrigerant, Void Fraction, and Homogeneous
Mesures du coefficient de transfert de chaleur pour la condensation par convection forcee de melanges huile-refrigerant (R-12) dans un tube horizontal. A partir de ces mesures, on cherche une correlation pour calculer le coefficient de... more
Mesures du coefficient de transfert de chaleur pour la condensation par convection forcee de melanges huile-refrigerant (R-12) dans un tube horizontal. A partir de ces mesures, on cherche une correlation pour calculer le coefficient de transfert de chaleur dans un large domaine des parametres
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ABSTRACT Single crystals of pure and doped lead bromide were grown by the Bridgman method in different convective conditions. The convection level was varied by changing the thermal and solutal Rayleigh number. The homogeneity in... more
ABSTRACT Single crystals of pure and doped lead bromide were grown by the Bridgman method in different convective conditions. The convection level was varied by changing the thermal and solutal Rayleigh number. The homogeneity in refractive index, and hence the optical quality, was estimated by examining the optical distortion, birefringence interferograms, and laser scattering through the crystal. The optical quality of the crystal varied significantly with the variation of convection level during the crystal growth. The critical concentration of the solute was estimated for several values of growth velocity by numerical analysis at the thermal gradient of 20 K/cm.
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ABSTRACT Experiments were performed with pure and doped lead halides to investigate growth conditions for large crystals. Direct observations during the growth of 25 mm diameter crystal growing at high velocities showed that torodial type... more
ABSTRACT Experiments were performed with pure and doped lead halides to investigate growth conditions for large crystals. Direct observations during the growth of 25 mm diameter crystal growing at high velocities showed that torodial type instability is formed at the solid/liquid interface during the growth. These instabilities translate into point defects and line defects. We report the results of extensive experiments on Lead bromide doped with silver bromide to study double diffusive transport. Control of instability at the interface provides a great improvement in the quality of crystal more specifically point defects and line defects. The controlled doping controls the defects and polytypism, and hence reduces the cracking and production of very large diameter good quality crystal is possible by Bridgman method. Results on the quality as the function of convection and growth parameters are reported in this paper.
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ABSTRACT The results from an experimental study of reduced-gravity two-phase flows are reported in this paper. The experiments were conducted in simulated reduced-gravity conditions in a ground-based test facility with a circular test... more
ABSTRACT The results from an experimental study of reduced-gravity two-phase flows are reported in this paper. The experiments were conducted in simulated reduced-gravity conditions in a ground-based test facility with a circular test section of 25mm inner diameter. The flow conditions for which data were acquired lie in the dispersed droplet to slug flow transition and slug flow regime. Local data were acquired for 17 different flow conditions at three axial locations. The acquired data complement and extend those discussed in an earlier paper by the authors (Vasavada etal. in, Exp Fluids 43: 53–75, 2007). The radial profiles and axial changes in the local data are analyzed and discussed in this paper. The area-averaged data, in conjunction with the local data, are discussed to highlight important interaction mechanisms occurring between fluid particles, i.e., drops. The data clearly show the effect of progressive coalescence leading to formation of slug drops. Furthermore, the shape of slug drops in reduced-gravity conditions was observed to be different from that in normal-gravity case. The analyses presented here show the presence of drop coalescence mechanisms that lead to the formation of slug drops and transition from dispersed droplet flow to the slug flow regime. The most likely causes of the coalescence mechanism are random collision of drops driven by turbulence eddies in the continuous phase and wake entrainment of smaller drops that follow preceding larger drops in the wake region. Data from flow conditions in which the breakup mechanism due to impact of turbulent eddies on drops illustrate the disintegration mechanism.
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Mixing of two fluids generated by steady and particularly g-jitter acceleration is fundamental towards the understanding of transport phenomena in a microgravity environment. We propose to carry out flight and ground-based experiments to... more
Mixing of two fluids generated by steady and particularly g-jitter acceleration is fundamental towards the understanding of transport phenomena in a microgravity environment. We propose to carry out flight and ground-based experiments to quantify flow fields due to g-jitter type of accelerations using Stereo Imaging Velocimetry (SIV), and measure the concentration field using laser fluorescence. The understanding of the effects of g-jitter on transport phenomena is of great practical interest to the microgravity community and impacts the design of experiments for the Space Shuttle as well as the International Space Station. The aim of our proposed research is to provide quantitative data to the community on the effects of g-jitter on flow fields due to mixing induced by buoyancy forces. The fundamental phenomenon of mixing occurs in a broad range of materials processing encompassing the growth of opto-electronic materials and semiconductors, (by directional freezing and physical vap...
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The chaotic advection of the interface between two miscible liquids inside a closed cavity, generated by a damped oscillatory buoyancy-driven (BD) regular flow field, is investigated experimentally for BD mixing. The Lagrangian history of... more
The chaotic advection of the interface between two miscible liquids inside a closed cavity, generated by a damped oscillatory buoyancy-driven (BD) regular flow field, is investigated experimentally for BD mixing. The Lagrangian history of interface motion, determined using the planar laser-induced fluorescence and the photographic full-field view method, is contrasted against the Eulerian flow field measured from particle image velocimetry. Chaotic advection stretches and folds the interface at an early stage to produce an asymmetric pairwise Rayleigh–Taylor (RT) morphology (RTM) structure from long wavelength RT instability and short-time Richtmyer–Meshkov instability and its fractal interface structure at a high impulsive-Reynolds number. The mechanism of folding, from global bifurcation of the flow field, caused by a hyperbolic point, served as an organizing center for multiple vortex interactions. The intermediate-stage kinematics of the RTM structure exhibits RT mixing and show...
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Transient mixing driven by buoyancy occurs through the birth of a symmetric Rayleigh-Taylor morphology (RTM) structure for large length scales. Beyond its critical bifurcation the RTM structure exhibits self-similarity and occurs on... more
Transient mixing driven by buoyancy occurs through the birth of a symmetric Rayleigh-Taylor morphology (RTM) structure for large length scales. Beyond its critical bifurcation the RTM structure exhibits self-similarity and occurs on smaller and smaller length scales. The dynamics of the RTM structure, its nonlinear growth and internal collision, show that its genesis occurs from an explosive bifurcation which leads to the overlap of resonance regions in phase space. This event shows the coexistence of regular and chaotic regions in phase space which is corroborated with the existence of horseshoe maps. A measure of local chaos given by the topological entropy indicates that as the system evolves there is growth of uncertainty. Breakdown of the dissipative RTM structure occurs during the transition from explosive to catastrophic bifurcation; this event gives rise to annihilation of the separatrices which drives overlap of resonance regions. The global bifurcation of explosive and catastrophic events in phase space for the large length scale of the RTM structure serves as a template for which mixing occurs on smaller and smaller length scales.
Research Interests: Applied Mathematics, Physics, Nonlinear dynamics, Fluid Dynamics, Entropy, and 12 moreSoftware, Chaos, Diffusion, Phase Space, Symmetry Breaking, Time Factors, Length scale, Catastrophe Theory, Numerical Analysis and Computational Mathematics, Topological Entropy, Rayleigh Taylor Instability, and Physical Phenomena
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