摘要 :
A modified polarographic method with inert gas for determination of the oxygen permeability in polymers immersed in liquids is described.Owing to the stream of an inert gas towards polymer from the cathode side,lateral oxygen diff...
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A modified polarographic method with inert gas for determination of the oxygen permeability in polymers immersed in liquids is described.Owing to the stream of an inert gas towards polymer from the cathode side,lateral oxygen diffusion (edge effects) is minimized.Unlike the standard Fatt method,the method with inert gas is suitable also for thick samples and,therefore,for high-permeable materials.Themethod was tested for prediction of oxygen permeability in poly(l-vinyl 2-pyrrolidone) (PVP) and poly(2-hydroxyethyl methacrylate) (PHEMA).As an electrolyte,solution of potassium chloride was used.The effect of additional resistances and small lateral diffusion was taken into account.Unexpectedly,oxygen permeability in both polymers was greater for 0.1 M KC1 than for 0.5 M KC1.The experimentalsetup was also used for diffusivity estimation in thick samples of PHEMA and PVP.Here,the oxygen flux response at one sample surface to the stepwise change in oxygen concentration at the other surface is measured and evaluated.The effect of the additional boundary layer on the oxygen transport is taken into account.A simple procedure for the diffusivity determination from the characteristic time of response as afunction of the sample thickness is given.Solubility of oxygen in polymer is calculated from the obtained permeability and diffusivity.
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Two perpendicular projections of rising bubbles were observed in counter-current downstream diverging flow. Evidently, the bubbles did not enter the boundary layer at the channel wall and a plug liquid flow assumption was acceptab...
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Two perpendicular projections of rising bubbles were observed in counter-current downstream diverging flow. Evidently, the bubbles did not enter the boundary layer at the channel wall and a plug liquid flow assumption was acceptable in our experimental equipment. This confirmed that the experiment was appropriate for simulation of bubble rises in a quiescent liquid column. Recent data obtained by a high-speed camera permitted recording over a period of 60 s. Image analysis by a tailor-made program provided a time-series of quantities related to the position, size, and shape of bubbles. In addition to determination of the aspect ratio of the equivalent oblate ellipsoid, deviation from this shape was investigated in respect of the difference between the bubble’s centre of mass and the geometrical centre of bubble projection. Autocorrelation of the data indicated that the bubble inclination oscillated harmonically with a frequency of 5–10 Hz; cross correlation showed that the horizontal shift of the centre of mass, as well as the horizontal velocity, increased with increasing bubble inclination, and the vertical shift of the centre of mass increased with an increases in the absolute value of the bubble inclination. There is no significant phase shift in the oscillation of these quantities. The bulky bottom side of the bubbles is in accordance with the model of bubble oscillation induced by instability of the equilibrium of gravity and surface tension forces. The oscillation frequency dependence on surface forces (E?tv?s number) is evident, while viscosity does not play a significant role in low-viscosity liquids. Therefore, vortex-shedding is more likely to be an effect of the oscillation and not its cause.
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Recycling is extremely important for steelmaking. In developed countries,about 60% of steel is manufactured from scrap. The scrap contains 0.5% of zinc in average,and this percentage steadily increases. During the steelmaking proc...
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Recycling is extremely important for steelmaking. In developed countries,about 60% of steel is manufactured from scrap. The scrap contains 0.5% of zinc in average,and this percentage steadily increases. During the steelmaking process both in basic oxygen furnaces (BOF) and in electric arc furnaces (EAF),all volatile zinc is released and forms airborne particles of dust. About 20 kg of dust is produced per 1 t of steel. A conservative estimate is that 10 Mt of the dust is produced yearly throughout the world. It contains about 1.5 Mt of zinc,which is still mostly dumped as a dangerous waste. This paper present a method of zinc recycling employing gaseous hydrogen chloride at 900 °C.
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摘要 :
For investigation of diffusion, such experimental setup geometry arrangement is preferred, where as soon as possible homogeneous concentration field takes place in flat material samples. However, lateral mass transfer may play sig...
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For investigation of diffusion, such experimental setup geometry arrangement is preferred, where as soon as possible homogeneous concentration field takes place in flat material samples. However, lateral mass transfer may play significant role. Here, this effect was solved for twodimensional diffusion through a layer of finite thickness to a circular target with an insulating ring. Simple formula has been suggested fitting the numerical results in a wide range of variables including asymptotic cases as well. The formula is suitable for determination of permeability using data received by electrodiffusion measurement under the conditions of limiting diffusion current to a circular electrode with a guard ring.
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