Density equilibration in a near‐critical fluid under reduced gravity

Ikier, Christian; Klein, H.; Woermann, D.

doi:10.1002/bbpc.19961000807

Cited by 2 publications

(1 citation statement)

References 13 publications

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“…In contrast to the short time scale of the thermal response, experimenters have observed a much longer time scale for the equilibration of density variations [36,15]. Near the critical point, the divergence of the compressibility and the influence of gravity can create strong macroscopic density gradients (upon which microscopic density fluctuations are superimposed).…”

Section: Introductionmentioning

confidence: 99%

Models of low-speed flow for near-critical fluids with gravitational and capillary effects

Denny¹,

Pego²

2000

Quart. Appl. Math.

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Abstract.We study low-speed flows of a highly compressible, single-phase fluid in the presence of gravity, for example, in a regime appropriate for modeling recent spaceshuttle experiments on fluids near the liquid-vapor critical point. In the equations of motion, we include forces due to capillary stresses that arise from a contribution made by strong density gradients to the free energy. We derive formally simplified sets of equations in a low-speed limit analogous to the zero Mach number limit in combustion theory.When viscosity is neglected and gravity is weak, the simplified system includes: a hyperbolic equation for velocity, a parabolic equation for temperature, an elliptic equation related to volume expansion, an integro-differential equation for mean pressure, and an algebraic equation (the equation of state). Solutions are determined by initial values for the mean pressure, the temperature field, and the divergence-free part of the velocity field. To model multi-dimensional flows with strong gravity, we offer an alternative to the anelastic approximation, one which admits stratified fluids in thermodynamic equilibrium, as well as gravity waves but not acoustic waves.1. Introduction. Near the liquid-vapor critical point, many of the thermophysical properties of a fluid exhibit a singular behavior. For instance, the isothermal compressibility and the isobaric thermal expansion coefficients, as well as the isobaric specific heat, all diverge strongly at the critical point. Critical enhancement effects are also encountered in the behavior of the thermal conductivity and the viscosity in the vicinity of the critical point, while the thermal diffusivity approaches zero. These singularities play a major role in the thermal equilibration of near-critical fluids.Understanding the effect of singular fluid properties on dynamics is not always straightforward. For example, it has been shown that even though thermal diffusivity is small,

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Section: Introductionmentioning

confidence: 99%

Models of low-speed flow for near-critical fluids with gravitational and capillary effects

Denny¹,

Pego²

2000

Quart. Appl. Math.

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Critical phenomena in microgravity: Past, present, and future

et al. 2007

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This review provides an overview of the progress in using the low-gravity environment of space to explore critical phenomena and test modern theoretical predictions. Gravity-induced variations in the hydrostatic pressure and the resulting density gradients adversely affect ground-based measurements near fluid critical points. Performing measurements in a low-gravity environment can significantly reduce these difficulties. A number of significant experiments have been performed in low-Earth orbit. Experiments near the lambda transition in liquid helium explored the regime of large correlation lengths and tested the theoretical predictions to a level of precision that could not be obtained on Earth. Other studies have validated theoretical predictions for the divergence in the viscosity as well as the unexpected critical speeding up of the thermal equilibrium process in pure fluids near the liquid-gas critical point. We describe the scientific content of previously flown low-gravity investigations of critical phenomena as well as those in the development stage, and associated ground-based work.

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Density equilibration in a near‐critical fluid under reduced gravity

Cited by 2 publications

References 13 publications

Models of low-speed flow for near-critical fluids with gravitational and capillary effects

Models of low-speed flow for near-critical fluids with gravitational and capillary effects

Critical phenomena in microgravity: Past, present, and future

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