Marangoni Convection in Radiating Fluids

1987 ◽  
Vol 109 (3) ◽  
pp. 717-721 ◽  
Author(s):  
Y. Bayazitoglu ◽  
T. T. Lam
Keyword(s):  
Marangoni Convection ◽  
Fluid Layer ◽  
Lower Surface ◽  
Linear Stability Theory ◽  
Critical Conditions ◽  
Microgravity Environment ◽  
Wide Range ◽  
Critical Marangoni Number ◽  
Radiating Fluids ◽  
Convective Fluid

The onset of Marangoni convection driven by surface tension gradients in radiating fluid layers is studied. The system considered consists of a fluid layer of infinite horizontal extent which is confined between a free upper surface and a rigid isothermal lower surface. The radiative boundaries of black–black, mirror–mirror, and black–mirror are considered. The critical conditions leading to the onset of convective fluid motions in a microgravity environment are determined numerically by linear stability theory. The perturbation equations are solved as a Bolza problem in the calculus of variations. The results are presented in terms of the critical Marangoni number and optical thickness for a wide range of some radiative parameters, including the Planck number, nongrayness of the fluid, and the emissivity of the boundaries. It is found that radiation suppresses Marangoni convection during material processing in space.

The effects of thermal modulation upon the onset of Marangoni–Bénard convection

2002 ◽  
Vol 456 ◽  
pp. 161-182 ◽  
Author(s):  
A. C. OR ◽  
R. E. KELLY
Keyword(s):  
Heat Flux ◽  
Free Surface ◽  
Fluid Layer ◽  
Linear Stability Theory ◽  
Modulation Amplitude ◽  
Thermal Modulation ◽  
Onset Of Convection ◽  
Long Wavelength ◽  
Critical Marangoni Number ◽  
The Mean

The effects of thermal modulation with time on the thermocapillary instability of a thin horizontal fluid layer with a deformable free surface are investigated on the basis of linear stability theory. First, a sinusoidal heating with a mean component is applied at the lower wall, corresponding to boundary conditions either in the form of prescribed temperature or heat flux. For finite-wavelength convection the thermal modulation exerts a strong effect, giving rise to a family of looped regions of instability corresponding to alternating synchronous or subharmonic responses. In the case of prescribed heat flux, the critical curve consists of significantly fewer loops than in the case of prescribed temperature. Thermal modulation with moderate modulation amplitude tends to stabilize the mean basic state, and optimal values of frequency and amplitude of modulation are determined to yield maximum stabilization. However, large-amplitude modulation can be destabilizing. A basic state with zero mean is then considered and the critical Marangoni number is obtained as a function of frequency. The effects of modulation are also investigated in the long-wavelength limit. For the case of prescribed temperature, the modulation does not affect the onset of the long-wavelength mode associated with the mean basic state and a purely oscillating basic state is always stable with respect to long-wavelength disturbances. For the case of prescribed heat flux both at the wall and free surface, by contrast, thermal modulation exerts a significant effect on the onset of convection from a mean basic state and long-wavelength convection can occur even for a purely oscillating basic state. The modulation can be stabilizing or destabilizing, depending on the frequency.

The Effect of Suction on the Stability of Fluid between Horizontal Plates at Differing Temperatures

1985 ◽  
Vol 199 (2) ◽  
pp. 145-151 ◽  
Author(s):  
M M Sorour ◽  
M A Hassab ◽  
F A Elewa
Keyword(s):  
Rayleigh Number ◽  
Fluid Layer ◽  
Critical Rayleigh Number ◽  
Linear Stability Theory ◽  
Stability Criteria ◽  
Thermal Boundary Conditions ◽  
Wide Range ◽  
Fluid Layers ◽  
The Stability ◽  
Horizontal Fluid Layer

The linear stability theory is applied to study the effect of suction on the stability criteria of a horizontal fluid layer confined between two thin porous surfaces heated from below. This investigation covers a wide range of Reynolds number 0 ≥ Re ≥ 30, and Prandtl number 0.72 ≥ Pr ≥ 100. The results show that the critical Rayleigh number increases with Peclet number, and is independent of Pr as far as Re < 3. However, for Re > 3 the critical Rayleigh number is function of both Pr and Pe. In addition, the analysis is extended to study the effect of suction on the stability of two special superimposed fluid layers. The results in the latter case indicate a more stabilizing effect. Furthermore, the effect of thermal boundary conditions is also investigated.

Marangoni convection in an ewline Oldroyd-B fluid layer with ewline throughflow

2007 ◽  
Vol 85 (9) ◽  
pp. 947-955 ◽  
Author(s):  
S Saravanan
Keyword(s):  
Approximate Solution ◽  
Marangoni Number ◽  
Marangoni Convection ◽  
Fluid Layer ◽  
Linear Analysis ◽  
Wave Number ◽  
Retardation Time ◽  
Viscoelastic Parameters ◽  
Critical Marangoni Number ◽  
The Galerkin Method

The onset of Marangoni convection in a horizontal Oldroyd-B fluid layer in the presence of a vertical throughflow is determined by linear analysis. We find an approximate solution to the corresponding eigenvalue problem using the Galerkin method. The effects of viscoelastic parameters on the critical Marangoni number, wave number, and frequency are discussed. The study also reveals the existence of a critical retardation time for which the oscillatory motion reaches its maximum strength. This study has possible implications in microgravity situations. PACS No.: 47.20.Gv

Stabilization of the no-motion state in the Rayleigh–Bénard problem

1994 ◽  
Vol 447 (1931) ◽  
pp. 587-607 ◽  
Keyword(s):  
Fluid Layer ◽  
Critical Rayleigh Number ◽  
Control Flow ◽  
Feedback Controller ◽  
Linear Stability Theory ◽  
Motion State ◽  
Conduction State ◽  
Bénard Problem ◽  
Benard Problem ◽  
Rayleigh Benard

Using linear stability theory and numerical simulations, we demonstrate that the critical Rayleigh number for bifurcation from the no-motion (conduction) state to the motion state in the Rayleigh–Bénard problem of an infinite fluid layer heated from below and cooled from above can be significantly increased through the use of a feedback controller effectuating small perturbations in the boundary data. The controller consists of sensors which detect deviations in the fluid’s temperature from the motionless, conductive values and then direct actuators to respond to these deviations in such a way as to suppress the naturally occurring flow instabilities. Actuators which modify the boundary’s temperature or velocity are considered. The feedback controller can also be used to control flow patterns and generate complex dynamic behaviour at relatively low Rayleigh numbers.

On the linear stability theory of Bénard–Marangoni convection

1989 ◽  
Vol 1 (7) ◽  
pp. 1123-1127 ◽  
Author(s):  
Rafael D. Benguria ◽  
M. Cristina Depassier
Keyword(s):  
Linear Stability ◽  
Stability Theory ◽  
Marangoni Convection ◽  
Linear Stability Theory

Stabilization of the No-Motion State of a Horizontal Fluid Layer Heated From Below With Joule Heating

1995 ◽  
Vol 117 (2) ◽  
pp. 329-333 ◽  
Author(s):  
J. Tang ◽  
H. H. Bau
Keyword(s):  
Joule Heating ◽  
Fluid Layer ◽  
Control Strategies ◽  
Critical Rayleigh Number ◽  
Linear Stability Theory ◽  
Small Perturbations ◽  
Motion State ◽  
Conduction State ◽  
Rayleigh Numbers ◽  
Horizontal Fluid Layer

Using linear stability theory and numerical simulations, we demonstrate that the critical Rayleigh number for bifurcation from the no-motion (conduction) state to the motion state in the Rayleigh–Be´nard problem of an infinite fluid layer heated from below with Joule heating and cooled from above can be significantly increased through the use of feedback control strategies effecting small perturbations in the boundary data. The bottom of the layer is heated by a network of heaters whose power supply is modulated in proportion to the deviations of the temperatures at various locations in the fluid from the conductive, no-motion temperatures. Similar control strategies can also be used to induce complicated, time-dependent flows at relatively low Rayleigh numbers.

The taxonomic status of the genus Rubidgea

Bothalia ◽  
1977 ◽  
Vol 12 (2) ◽  
pp. 313-317 ◽  
Author(s):  
Éva Kovács-Endrődy
Keyword(s):  
South Africa ◽  
Type Species ◽  
Taxonomic Status ◽  
Lower Surface ◽  
Carbonaceous Shale ◽  
Single Leaf ◽  
Wide Range

The genus Rubidgea Tate of the fossil family Glossopteridaceae was reduced to a synonym of Glossopteris by Seward (1907). Seward’s conclusion is now confirmed by a study of a wide range of imprints from a quarry near Hammanskraal, South Africa. The upper and lower surface imprints of a single leaf found on a split fragment of carbonaceous shale provides the main evidence presented. The finely striated upper surface imprint of the leaf could be identified with  Rubidgea, whereas the lower surface imprint represents the typical strong venation of a  Glossopteris. The type species of  Rubidgea is transferred to  Glossopteris as  G. mackayi (Tate) Kovacs comb. nov. The characteristics of upper and lower surface imprints of a number of  Glossopteris species are discussed.

Influence of Mechanical Surface Treatments on the Fatigue Performance of the Gamma TiAl Alloy Ti-45Al-9Nb-0.2C

2007 ◽  
Vol 539-543 ◽  
pp. 1553-1558 ◽  
Author(s):  
Janny Lindemann ◽  
Anja Kutzsche ◽  
Michael Oehring ◽  
Fritz Appel
Keyword(s):  
Surface Roughness ◽  
Shot Peening ◽  
Tial Alloy ◽  
Elevated Temperatures ◽  
Lower Surface ◽  
Fatigue Performance ◽  
Ambient Temperatures ◽  
Roller Burnishing ◽  
Compressive Stresses ◽  
Wide Range

The effect of shot peening and roller burnishing on the fatigue performance of the γ(TiAl) alloy Ti-45Al-9Nb-0.2C was investigated over a wide range of processing intensities. At optimized conditions shot peening and roller burnishing can markedly improve the fatigue strength at ambient temperatures. For temperatures above 650 °C, the residual compressive stresses induced by shot peening and roller burnishing quickly relax. This indicates that, at elevated temperatures, surface roughness and dislocation strengthening become more important for the fatigue performance of mechanically surface-treated components. Roller burnishing leads to much lower surface roughness than shot peening, resulting in more effective improvement of high temperature fatigue performance. However, surface strengthening by shot peening can also be beneficial for the fatigue performance at elevated temperatures, when the surface roughness is reduced by subsequent polishing.

Experimental investigation of convective stability in a superposed fluid and porous layer when heated from below

1989 ◽  
Vol 207 ◽  
pp. 311-321 ◽  
Author(s):  
Falin Chen ◽  
C. F. Chen
Keyword(s):  
Porous Layer ◽  
Fluid Layer ◽  
Critical Rayleigh Number ◽  
Linear Stability Theory ◽  
Convective Stability ◽  
Onset Of Convection ◽  
Temperature Distributions ◽  
Critical Wavelength ◽  
Crystal Film ◽  
Flux Curve

Experiments have been carried out in a horizontal superposed fluid and porous layer contained in a test box 24 cm × 12 cm × 4 cm high. The porous layer consisted of 3 mm diameter glass beads, and the fluids used were water, 60% and 90% glycerin-water solutions, and 100% glycerin. The depth ratio ď, which is the ratio of the thickness of the fluid layer to that of the porous layer, varied from 0 to 1.0. Fluids of increasingly higher viscosity were used for cases with larger ď in order to keep the temperature difference across the tank within reasonable limits. The top and bottom walls were kept at different constant temperatures. Onset of convection was detected by a change of slope in the heat flux curve. The size of the convection cells was inferred from temperature measurements made with embedded thermocouples and from temperature distributions at the top of the layer by use of liquid crystal film. The experimental results showed (i) a precipitous decrease in the critical Rayleigh number as the depth of the fluid layer was increased from zero, and (ii) an eightfold decrease in the critical wavelength between ď = 0.1 and 0.2. Both of these results were predicted by the linear stability theory reported earlier (Chen & Chen 1988).

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