The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform

Nicholas D Kazarinoff - One of the best experts on this subject based on the ideXlab platform.

  • recent results on surface tension driven convection in cylindrical Float Zones
    Advances in Space Research, 1991
    Co-Authors: Nicholas D Kazarinoff
    Abstract:

    Abstract The role and effects of surface tension in the development and continuation of oscillations in cylindrical Float-Zones is discussed. Results for different values of the equilibrium surface tension are compared. A physical mechanism is given for the continuation of asymmetric, axial oscillations of toroidal flow cells in such Float-Zones.

  • bifurcations of numerically simulated thermocapillary flows in axially symmetric Float Zones
    Physics of Fluids, 1990
    Co-Authors: Nicholas D Kazarinoff, Joseph S Wilkowski
    Abstract:

    Two‐dimensional time‐dependent flow in an axially symmetric liquid bridge of Si at zero g with flat ends at the melting temperature θM of Si driven by motions of the free, lateral surface is studied numerically. The system is energized by a ring heater H at temperature θH>θM that surrounds the midcircle m of the bridge. The radiation from H creates a ∇σS(δS is surface temperature), which in turn creates a ∇σ (σ is surface tension) that drives oscillations of its free surface and thermocapillary flow in the bridge. For aspect ratios A of (1)/(2) , (2)/(3) , and 1 it is found that as the relevant control parameter Δθ≡θH−θM is increased, the flow in the bridge bifurcates differently depending on A. For A= (1)/(2) and (2)/(3) the flow bifurcates from steady state to small‐amplitude periodic oscillations, breaking symmetry, to large‐amplitude, period‐tripled ones, to their subharmonics, then becomes aperiodic, and finally chaotic. Toroidal cells in the bridge oscillate to‐and‐fro along its axis as a compound p...

C A Winter - One of the best experts on this subject based on the ideXlab platform.

  • effects of g jitter and marangoni convection on Float Zones
    Journal of Spacecraft and Rockets, 1992
    Co-Authors: N Ramachandran, C A Winter
    Abstract:

    The effects of £-jitter on three liquid zone experiments are numerically investigated. The g -level used in the study is composed of a steady component, characterizing the residual acceleration environment, and a timevarying component, characterizing the £-jitter environment. The time-varying component is comprised of either a sinusoidal or impulse disturbance. The response of both unencapsulated and encapsulated zone configurations are examined. The results indicate that complex flow patterns can arise that significantly modify the heat transfer characteristics of the system. The effects are more pronounced at the lowest frequency investigated (10 ~3 Hz), and impulsive accelerations imparted to fluids with large Prandtl numbers were found to have long decay times. Detailed velocity, temperature, average Nusselt number, and temperature sensitivity information are presented for many of the cases investigated.

  • the effects of g jitter and surface tension induced convection on Float Zones
    28th Aerospace Sciences Meeting, 1990
    Co-Authors: N Ramachandran, C A Winter
    Abstract:

    The effects of g-jitter on nonencapsulated and encapsulated liquid bridges were investigated numerically, using fluid characteristics and parameters from three fluid systems: a silicone oil bridge, a methanol bridge, and a silicon melt. Results showed that complex flow patterns can arise in g-jitter environment which significantly modify the heat-transfer characteristics of the system. It was found that the nonencapsulated liquid bridges and Float zone melts were dominated by surface-tension driven convection, with very little impact on the flows by residual and g-jitter accelerations. Zone encapsulation resulted in a sizeable drop in the maximum fluid velocities. The g-jitter computations on the encapsulated Float Zones resulted in significant augmentation of the maximum velocities and heat transfer, with the silicon melt being the least sensitive to g-jitter acceleration.

N Ramachandran - One of the best experts on this subject based on the ideXlab platform.

  • effects of g jitter and marangoni convection on Float Zones
    Journal of Spacecraft and Rockets, 1992
    Co-Authors: N Ramachandran, C A Winter
    Abstract:

    The effects of £-jitter on three liquid zone experiments are numerically investigated. The g -level used in the study is composed of a steady component, characterizing the residual acceleration environment, and a timevarying component, characterizing the £-jitter environment. The time-varying component is comprised of either a sinusoidal or impulse disturbance. The response of both unencapsulated and encapsulated zone configurations are examined. The results indicate that complex flow patterns can arise that significantly modify the heat transfer characteristics of the system. The effects are more pronounced at the lowest frequency investigated (10 ~3 Hz), and impulsive accelerations imparted to fluids with large Prandtl numbers were found to have long decay times. Detailed velocity, temperature, average Nusselt number, and temperature sensitivity information are presented for many of the cases investigated.

  • the effects of g jitter and surface tension induced convection on Float Zones
    28th Aerospace Sciences Meeting, 1990
    Co-Authors: N Ramachandran, C A Winter
    Abstract:

    The effects of g-jitter on nonencapsulated and encapsulated liquid bridges were investigated numerically, using fluid characteristics and parameters from three fluid systems: a silicone oil bridge, a methanol bridge, and a silicon melt. Results showed that complex flow patterns can arise in g-jitter environment which significantly modify the heat-transfer characteristics of the system. It was found that the nonencapsulated liquid bridges and Float zone melts were dominated by surface-tension driven convection, with very little impact on the flows by residual and g-jitter accelerations. Zone encapsulation resulted in a sizeable drop in the maximum fluid velocities. The g-jitter computations on the encapsulated Float Zones resulted in significant augmentation of the maximum velocities and heat transfer, with the silicon melt being the least sensitive to g-jitter acceleration.

Joseph S Wilkowski - One of the best experts on this subject based on the ideXlab platform.

  • bifurcations of numerically simulated thermocapillary flows in axially symmetric Float Zones
    Physics of Fluids, 1990
    Co-Authors: Nicholas D Kazarinoff, Joseph S Wilkowski
    Abstract:

    Two‐dimensional time‐dependent flow in an axially symmetric liquid bridge of Si at zero g with flat ends at the melting temperature θM of Si driven by motions of the free, lateral surface is studied numerically. The system is energized by a ring heater H at temperature θH>θM that surrounds the midcircle m of the bridge. The radiation from H creates a ∇σS(δS is surface temperature), which in turn creates a ∇σ (σ is surface tension) that drives oscillations of its free surface and thermocapillary flow in the bridge. For aspect ratios A of (1)/(2) , (2)/(3) , and 1 it is found that as the relevant control parameter Δθ≡θH−θM is increased, the flow in the bridge bifurcates differently depending on A. For A= (1)/(2) and (2)/(3) the flow bifurcates from steady state to small‐amplitude periodic oscillations, breaking symmetry, to large‐amplitude, period‐tripled ones, to their subharmonics, then becomes aperiodic, and finally chaotic. Toroidal cells in the bridge oscillate to‐and‐fro along its axis as a compound p...

A V Anilkumar - One of the best experts on this subject based on the ideXlab platform.

  • experiments on suppression of thermocapillary oscillations in Float Zones by high frequency end wall vibrations
    2003
    Co-Authors: A V Anilkumar, Richard N Grugel, J Bhowmick, T G Wang
    Abstract:

    Experiments to suppress thermocapillary oscillations using high-frequency vibrations were performed on Float-Zones. Such a Float-zone is formed by melting one end of a vertically held sodium nitrate-barium nitrate crystal rod in contact with a hot surface at the top. In the experiments, when thermocapillary oscillation occurred, the bottom end of the rod was vibrated at a high frequency to generate fine ripples on the melt surface, driving a streaming flow in the opposite direction to that of the thermocapillary convection. It was observed that by generating a sufficiently strong streaming flow the thermocapillary flow can be offset enough such that the associated thermocapillarity oscillations can be quenched.

  • Role of Vibration-Induced Streaming in Float-Zone Crystal Growth
    39th Aerospace Sciences Meeting and Exhibit, 2001
    Co-Authors: A V Anilkumar, R. N. Grugel, M. Franklin Rose
    Abstract:

    This presentation will examine in detail the role of vibration-induced streaming flow in the context of Float-zone crystal growth. It is very well known that during Float-zone materials processing, the naturally occurring temperature gradients along the zone surface impose a thermocapillary flow in the zone. Under certain processing conditions, the thermocapillary flow can also become nonsteady (oscillatory). The presence of thermocapillary flow is detrimental to crystal quality, for it can promote non-uniform dopant distribution and crystal striations. To null this effect we have imposed a counter streaming flow in the zone, via end-wall vibration. This technique has been adapted to Float-zone processing of Sodium Nitrate-Barium Nitrate eutectic alloys, under both steady and nonsteady thermocapillary flow conditions. The beneficial effects of counter streaming flow have been clearly brought out through the before and after comparisons of the crystal microstructure. In addition, we are also examining the theoretical underpinnings of the balancing of thermocapillary flows with vibration-driven counter flows in Float-Zones.