We measure the turbulent diffusion coefficient of dust grains embedded in magnetorotational turbulence in a protoplanetary disc directly from numerical simulations and compare it to the turbulent viscosity of the flow. The simulations are done in a local coordinate frame comoving with the gas in Keplerian rotation. Periodic boundary conditions are used in all directions, and vertical gravity is...

- The mechanism of diffusion layer growth in plasma nitrided coatings applied on a St52 steel using an active screen is investigated. The nitriding was performed at 450,500 and 550 ◦C temperature nitriding times of 5, 10 and 15 h, in a gas mixture containing 20 vol. % H2: 80 vol. % N2 and DC-pulsed plasma nitriding unit. The surface, cross section and the thickness of diffusion of specimens ...

This paper explores the mathematical formulations of Fick and MaxwellStefan diffusion in the context of polymer electrolyte membrane fuel cell cathode gas diffusion layers. Formulations of diffusion combined with mass-averaged Darcy flow are considered for three component gases. Fick formulations can be considered as approximations of Maxwell-Stefan in a certain sense. For this application, the...

This work presents new design of a gas diffusion unit, called 'membraneless gas diffusion (MGD) unit', which, unlike a conventional gas diffusion (GD) unit, allows selective detection of volatile compounds to be made without the need of a hydrophobic membrane. A flow injection method was developed employing the MGD unit to determine ethanol in alcoholic drinks based on the reduction of dichroma...

A novel metallic porous medium with improved thermal and electrical conductivities and controllable porosity was developed based on micro/nano echnology for its potential application in PEM fuel cells. In this work to demonstrate its applicability, the gas diffusion medium, made of 12.5 m hick copper foil, was tested in an operational fuel cell. The small thickness and straight-pore feature of ...

Solid oxide fuel cell (SOFC) is a promising alternative energy source, with its advantages of high operating efficiency, fuel flexibility, low emissions and relatively low cost. However, there are several challenges concerning the SOFC research. Little is known about the complex interfacial electrochemistry and thermochemistry, and it is also difficult to diagnose problems and optimize cell per...

The effects of fluid viscoelasticity on the expansion of gas bubbles in polymer foams for the cases of reactive and non-reactive polymers are investigated. For non-reactive polymers, bubble expansion is controlled by a combination of gas diffusion and fluid rheology. In the diffusion limited case, the initial growth rate is slow due to small surface area, whereas at high diffusivity initial gro...

We present a self-consistent mean field theory of the dynamo in 3D and turbulent diffusion in 2D in weakly ionized gas. We find that in 3D, the backreaction does not alter the beta effect while it suppresses the alpha effect when the strength of a mean magnetic field exceeds the critical value Bc ∼ √ νinτn〈v2〉/Rm. Here, νin, τn, and Rm are ion-neutral collision frequency, correlation time of ne...

channel pores where no very long jumps are possible. For pores with an elevation that varies like a random walk (red) and alternating pores (blue) the scaled mean square displacement /t is asymp-totically constant. 1. Introduction In general, diffusion of gas particles depends on the collisions between the gas molecules as well as on the collisions of the gas with the pore walls. Of pa...

In this article we develop Poincaré ideas about a heat balance of ideal gas considered as a collisionless continuous medium. We obtain the theorems on diffusion in nondegenerate completely integrable systems. As a corollary we show that for any initial distribution the gas will be eventually irreversibly and uniformly distributed over all volume, although every particle during this process appr...