On the convective contamination of diffusivity measurements in liquids

Alexander, J. Iwan D.; Rosenberger, Franz

doi:10.2514/6.1997-571

Cited by 3 publications

(4 citation statements)

References 5 publications

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“…Despite this, both results yielded perfectly Gaussian C( x ) plots. Our numerical modeling efforts have shown that only the most extreme convective contamination (several hundred percent) leads to nonlinearities in these graphs 2. We have experimentally confirmed these results in horizontally and vertically oriented ampoules.…”

Section: Introductionsupporting

confidence: 72%

“…Thus, in liquids, the attainment of diffusion‐dominated transport over macroscopic distances at normal gravity is obviously not a simple task. Numerical modeling efforts in our group and others has shown that in liquid metals, with their typical viscosities of 10 −3 poise, temperature nonuniformities of a few hundredths of a degree are sufficient to generate convective contributions equal to the diffusive flux 2. Thus, even in systems with essentially no measurable temperature nonuniformities, convective fluxes may be the dominant mode of transport 3…”

Section: Introductionmentioning

confidence: 97%

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Mass and Thermal Diffusivity Algorithms

Banish

Albert

Pourpoint

et al. 2002

Annals of the New York Academy of Sciences

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Mass and thermal diffusivity measurements conducted on Earth are prone to contamination by uncontrollable convective contributions to the overall transport. Previous studies of mass and thermal diffusivities conducted on spacecraft have demonstration the gain in precision, and lower absolute values, resulting from the reduced convective transport possible in a low-gravity environment. We have developed and extensively tested real-time techniques for diffusivity measurements, where several measurements may be obtained on a single sample. This is particularly advantageous for low gravity research were there is limited experiment time. The mass diffusivity methodology uses a cylindrical sample geometry. A radiotracer, initially located at one end of the host is used as the diffusant. The sample is positioned in a concentric isothermal radiation shield with collimation bores located at defined positions along its axis. The intensity of the radiation emitted through the collimators is measured versus time with solid-state detectors and associated energy discrimination electronics. For the mathematical algorithm that we use, only a single pair of collimation bores and detectors are necessary for single temperature measurements. However, by employing a second, offset, pair of collimation holes and radiation detectors, diffusivities can be determined at several temperatures per sample. For thermal diffusivity measurements a disk geometry is used. A heat pulse is applied in the center of the sample and the temperature response of the sample is measured at several locations. Thus, several values of the diffusivity are measured versus time. The exact analytic solution to a heat pulse in the disk geometry leads to a unique heated area and measurement locations. Knowledge of the starting time and duration of he heating pulse is not used in the data evaluation. Thus, this methodology represents an experimentally simpler and more robust scheme.

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Section: Introductionsupporting

confidence: 72%

Section: Introductionmentioning

confidence: 97%

Mass and Thermal Diffusivity Algorithms

Banish

Albert

Pourpoint

et al. 2002

Annals of the New York Academy of Sciences

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“…To minimize as much as possible these perturbations, capillary tubes of different diameters [1,2], stabilizing vertical gradients and magnetic fields [3][4][5][6][7][8][9][10] have been extensively used. Nevertheless, despite all these corrective strategies some related problems still arise.…”

Section: Introductionmentioning

confidence: 99%

On the accuracy of the interdiffusion measurements at low and moderate Rayleigh numbers. Some computational considerations

Ruíz

Pallarès

Grau

2010

International Journal of Heat and Mass Transfer

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“…Under gravity diffusion measurements can be disturbed by buoyancy e.g. due to inhomogeneous temperature distribution Alexander et al (1996). Measurements of self-diffusion in liquid pure metals sometimes lead to diffusion coefficients that were too high due to additional mass transport by convection.…”

Section: Experiments Under Different Gravity Conditionsmentioning

confidence: 99%

Influence of Gravity on Atomic Mobility in a Liquid

Sondermann

Voigtmann

Meyer

2022

Microgravity Sci. Technol.

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Measurements of diffusion and thermodiffusion in liquids are very sensitive to convection caused for example by buoyancy. To reduce the impact of buoyancy-driven convection, benchmark experiments are performed in microgravity conditions. Here, we discuss the general influence of gravity on atomic mobility. The gravitational Péclet number and the gravitational length can be used to assess this influence. They show that the diffusion processes of atoms in a liquid is not affected by Earth’s gravitational force but that the process is dominated by the thermal energy of the atoms. Data from experiments under different gravity conditions ranging from $$10^{-5}g$$ 10 - 5 g to $$10^6g$$ 10 6 g are summarized. They confirm that interdiffusion is only influenced by accelerations that are orders of magnitude larger than Earth’s gravity.

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On the convective contamination of diffusivity measurements in liquids

Cited by 3 publications

References 5 publications

Mass and Thermal Diffusivity Algorithms

Mass and Thermal Diffusivity Algorithms

On the accuracy of the interdiffusion measurements at low and moderate Rayleigh numbers. Some computational considerations

Influence of Gravity on Atomic Mobility in a Liquid

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