<i>Bénard Cells and Taylor Vortices</i>

Koschmieder, E. L.; Andereck, C. David

doi:10.1063/1.2808501

Cited by 242 publications

(376 citation statements)

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“…¥; no temperature gradients in the plane of the surface), surface cooling generates a layer of liquid of enhanced density overlaying a bulk zone of warmer liquid having a lower density. As with the Be Ânard±Marangoni case, this system is not stable inde®nitely and remarkably similar equations apply [5], though high values of thermal diffusivity (k) and kinematic viscosity (n) with low values of thermal expansion (a) do act as stabilising in¯uences. As the driving force is increased, the quiescent boundary layer eventually breaks down at the limit of validity of the linearised Navier±Stokes amplitude equations and convection starts.…”

Section: The Rayleigh±be âNard Effectmentioning

confidence: 84%

“…Here the vertical component of thē uid velocity within a convecting boundary layer is given [5] by u z x; y V z 1 2 cos 2ky cos ky cos p 3kx ! where it should be understood that the cosine terms represent a hexagonally symmetrized translationally invariant standing wave pattern of wavelength l 2p/k in the (x, y) plane, so one can imagine the liquid¯owing in one vertical direction where the cosine terms are positive and in the reverse direction where they are negative.…”

Section: The Destabilizing Mechanismsmentioning

confidence: 99%

“…As the driving force is increased, the quiescent boundary layer eventually breaks down at the limit of validity of the linearised Navier±Stokes amplitude equations and convection starts. The thickness of the boundary layer at which this happens is characteristically larger than for the Be Ânard±Marangoni case [5] and is determined for the case considered by the critical value R c 667 of the Rayleigh number [5] …”

Section: The Rayleigh±be âNard Effectmentioning

confidence: 99%

“…Two patterns are important [5,6]: (a) parallel contrarotating cylindrical rolls and (b) hexagonal cells as with Be Ânard±Marangoni convection, but in which the cell centres are domed rather than saucer-shaped (dimpled), uid again rising towards the centre and falling down hexagonal cell walls as in Fig. 3 [22].…”

Section: The Rayleigh±be âNard Effectmentioning

confidence: 99%

“…A second process of thermal convection (Rayleigh±Be Ânard), which depends on density gradients within the boundary layer, sustains the ®rst process and tends to dominance once a critical value of the product DTd 3 is reached [5,6]. Again, as evaporation proceeds at constant DT, the boundary layer continues to thicken when, at a third critical stage, dense cold¯uid becomes detached from the boundary layer and plunges as columns towards the base of the vessel [7±11], leaving behind a thinned boundary layer depleted of cold¯uid.…”

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confidence: 99%

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A semiquantitative analysis of the dynamics of a Goldman‐type vaporiser

2000

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SummaryWhen a turbulent¯ow of a carrier gas is passed over a liquid anaesthetic agent contained in a vaporiser of Goldman design, evaporation from the cooled surface leads rapidly to a succession of uid instabilities which set in at characteristic critical conditions. An initially quiescent boundary layer at the surface is sequentially replaced by a thin layer of toroidal (Be Ânard±Marangoni) convection cells which are driven by surface tension gradients. These are then augmented by Rayleigh±Be Ânard convection driven by gravity, the whole process terminating in intermittent columnar plunging of cold¯uid from a chaotic surface layer of pulsating thickness to the base of the liquid pool. Residual striations from these plunging columns persist throughout the bulk of the liquid so long as evaporation continues. The ultimate state is then one in which turbulence occurs throughout both liquid and vapour phases. In this paper, a semiquantitative analysis of the system dynamics is given with supportive experimental evidence where possible. Modern anaesthetic vaporisers are large and complex devices having temperature compensation and designed for use in a steady¯ow of gas. They have a relatively high resistance to gas¯ow in order to reduce the effect of downstream pressure¯uctuations on vaporiser output. They are also calibrated, the concentration of agent emitted corresponding to the degree of rotation of the control knob being known. Both the temperature compensation and the calibration may be sources of error. In these vaporisers, saturation of gas by agent within the vaporising chamber is achieved by the use of wicks so that the gas is exposed to a large surface area of agent. The requirement of calibration and the use of wicks means that the vaporiser is agent speci®c. The nature of the gas¯ow through these vaporisers is not important except for the major proviso that the¯ow through either the bypass or the vaporising channels should not change from laminar to turbulent (or vice versa) at any point within the operating range of the vaporiser. If that did occur there would be a large and abrupt change in the calibration curve at that point.The availability of anaesthetic gas analysers for routine clinical use has changed the requirements governing the design of vaporisers. This is particularly true for systems using low fresh gas¯ows with which the concentration of agent inspired by the patient may not be the same as that delivered by the vaporiser. Three recent papers [1±3] have described the consistent and usable performance obtainable from simple vaporisers of the Goldman type mounted within circle systems (VIC). These uncalibrated vaporisers are of simple construction and have no temperature compensation. They have low resistance to gas¯ow and are not agent speci®c. The papers already referred to showed that vaporisers of this type had features useful in clinical practice. We have therefore undertaken an analysis of their physical performance believing that this would help improvement of the design of this type...

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Section: The Rayleigh±be âNard Effectmentioning

confidence: 84%

Section: The Destabilizing Mechanismsmentioning

confidence: 99%

Section: The Rayleigh±be âNard Effectmentioning

confidence: 99%

Section: The Rayleigh±be âNard Effectmentioning

confidence: 99%

mentioning

confidence: 99%

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A semiquantitative analysis of the dynamics of a Goldman‐type vaporiser

2000

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Parallel finite element solution of three-dimensional Rayleigh-Bénard-Marangoni flows

Carey

McLay

Bicken

et al. 1999

Int. J. Numer. Meth. Fluids

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Thermal Optofluidics: Principles and Applications

Chen

Loo

Wang

et al. 2019

Advanced Optical Materials

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Thermal optofluidics is an emerging field that promises to create numerous research and application opportunities in biophysics, biochemistry, and clinical biology. Innovation in plasmonic optics has led to the development of various invaluable tools in the fields of biosensing and microfluidic manipulation. The optothermal effect originates from light–matter interactions during photon–phonon conversion, which can lead to micro‐ or nanoscale inhomogeneities in the thermal distribution. This further induces a series of hydrodynamic phenomena such as natural convection, Marangoni convection, thermophoresis, the electrolyte Seebeck effect, depletion forces, and interfacial effects in colloidal particles. Light–matter interactions are particularly important for three aspects of microfluidics, namely the motion of colloidal particles, fluidic actuation, and biochemical reactions. This review first systematically elucidates the role of both nanoscale plasmonic thermal generation and heat‐induced fluidic motion in optofluidic microsystems. Then, recent state‐of‐the‐art thermal optofluidic applications of the above‐listed three aspects are presented. The paper aims to provide an insightful reference for future research in optofluidic biochemical systems.

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Bénard Cells and Taylor Vortices

Cited by 242 publications

References 0 publications

A semiquantitative analysis of the dynamics of a Goldman‐type vaporiser

A semiquantitative analysis of the dynamics of a Goldman‐type vaporiser

Parallel finite element solution of three-dimensional Rayleigh-Bénard-Marangoni flows

Thermal Optofluidics: Principles and Applications

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