Mass Transport Study of Combined Gas Phase and Surface Diffusion in Porous Glass Membrane

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The influence of hand positions on biomechanical injury risk factors at the wrist joint during the round-off skills in female gymnastics

The aim of this study was to examine the biomechanical injury risk factors at the wrist, including joint kinetics, kinematics and stiffness in the first and second contact limb for parallel and T-shape round-off (RO) techniques. Seven international-level female gymnasts performed 10 trials of the RO to back handspring with parallel and T-shape hand positions. Synchronised kinematic (3D motion analysis system; 247 Hz) and kinetic (two force plates; 1235 Hz) data were collected for each trial. A two-way repeated measure analysis of variance (ANOVA) assessed differences in the kinematic and kinetic parameters between the techniques for each contact limb. The main findings highlighted that in both the RO techniques, the second contact limb wrist joint is exposed to higher mechanical loads than the first contact limb demonstrated by increased axial compression force and loading rate. In the parallel technique, the second contact limb wrist joint is exposed to higher axial compression load. Differences between wrist joint kinetics highlight that the T-shape technique may potentially lead to reducing these bio-physical loads and consequently protect the second contact limb wrist joint from overload and biological failure. Highlighting the biomechanical risk factors facilitates the process of technique selection making more objective and safe

Study of Capillary Condensation of Butane in a Vycor Membrane

Knudsen diffusion, surface diffusion and Poiseuille flux of capillary condensate can contribute to the flux of a condensable gas in the small pores of Vycor membrane (pore radius 4 nm). It is very difficult to distinguish between individual the contributions, especially because the pores have no uniform pore diameter. Two basic types of experiments were made to study the transport mechanisms of a condensable gas (butane) through a Vycor membrane: steady state permeation and measurements of liquid flux. Steady state experiments enable to study butane transport for different concentration profiles in the pores. Measurements of liquid flux are indispensable for the verification of the presence of condensate in pores during gas permeation. Differences between the liquid butane flux (on high pressure side of membrane is liquid, on opposite side is gas) and the gas flux (at both sides butane is in the gas phase) for the same pressure gradients across the membrane were observed. The difference between these fluxes decreases with decreasing of pressure gradients. For a pressure gradient higher than 2 bars (liquid butane P1=2.25 bar; P2= 0 bar, gas butane P1=2.24 bar; P2= 0 bar) the flux of the liquid butane is approximately 2 times higher. The ratio of liquid and gas fluxes decreases to 1.7 for pressure conditions P1=2.24-2.25 and P2=0.98 bar. No difference between liquid and gas fluxes was registered for the low pressure gradient investigated (P1=2.22 bar; P2= 1.91 bar). It can be concluded that the condensation of butane in pores occurs at high pressures on both sides of pores if simultaneously the pressure difference is small

Transport of butane in a porous Vycor glass membrane in the region of condensation pressure

The transport and the separation efficiency in porous membranes can be strongly influenced by the condensation of permeating gases. An accurate experimental monitoring of permeating vapors and condensates in small pores of membranes is very desirable. The dynamic permeation method is one of the methods which can be used to perform a corresponding study. The following experimental arrangement was applied: a constant higher pressure P1 was set on an open side of the membrane; on the opposite closed side the change of a lower pressure P2 was measured. The dynamic permeation set-up was used at first in transport measurements of a noncondensable gas through a Vycor glass membrane (mean pore radius around 2 nm). The obtained data were compared with the results of alternatively performed steady state permeation measurements. Subsequently, the permeability was studied for the condensable gas butane through the Vycor glass membrane, particularly for elevator pressure conditions near the saturated vapor pressure. Also for this purpose the dynamic permeation experiment was found to be very convenient. It enables to measure the mass transport for very small pressure gradients across the membrane. The permeation results obtained correspond well with the liquid butane permeability of Vycor membrane quantified previously in independent pervaporation experiments. This agreement confirms the presence of liquid butane in small pores of Vycor glass during the transient gas transport at relatively high pressures. Copyright © 2007 Elsevier B.V. All rights reserved. [accessed 2013 November 26th

La migraine de l'enfant

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

An experimental study of combined gas phase and surface diffusion in porous glass

The diffusion of inert and adsorbable gases and binary gas mixtures through porous glass has been studied experimentally. A modified Wicke Kallenbach cell consisting of two gas compartments separated by a tubular mesoporous membrane was used. The scope of this paper is to quantify the contributions of gas phase and surface diffusion. Adopting the dusty gas model (DGM) for the description of gas phase mass transfer and a generalized Stefan Maxwell (GSM) theory to quantify surface diffusion a combined transport model has been applied. The DGM was found to be well suited for the description of transport through the pores. Surface diffusion of adsorbable gases was analyzed experimentally for different loadings. The obtained Fickian surface diffusivities were found to be strongly concentration dependent. Multicomponent surface diffusion is mainly affected by adsorption equilibrium. Reliable predictions require an accurate knowledge of the competitive adsorption isotherms

Study of Capillary Condensation of Butane in a Vycor Membrane

Knudsen diffusion, surface diffusion and Poiseuille flux of capillary condensate can contribute to the flux of a condensable gas in the small pores of Vycor membrane (pore radius 4 nm). It is very difficult to distinguish between individual the contributions, especially because the pores have no uniform pore diameter. Two basic types of experiments were made to study the transport mechanisms of a condensable gas (butane) through a Vycor membrane: steady state permeation and measurements of liquid flux. Steady state experiments enable to study butane transport for different concentration profiles in the pores. Measurements of liquid flux are indispensable for the verification of the presence of condensate in pores during gas permeation. Differences between the liquid butane flux (on high pressure side of membrane is liquid, on opposite side is gas) and the gas flux (at both sides butane is in the gas phase) for the same pressure gradients across the membrane were observed. The difference between these fluxes decreases with decreasing of pressure gradients. For a pressure gradient higher than 2 bars (liquid butane P1=2.25 bar; P2= 0 bar, gas butane P1=2.24 bar; P2= 0 bar) the flux of the liquid butane is approximately 2 times higher. The ratio of liquid and gas fluxes decreases to 1.7 for pressure conditions P1=2.24-2.25 and P2=0.98 bar. No difference between liquid and gas fluxes was registered for the low pressure gradient investigated (P1=2.22 bar; P2= 1.91 bar). It can be concluded that the condensation of butane in pores occurs at high pressures on both sides of pores if simultaneously the pressure difference is small