We describe the diffusion and random velocities of solid particles due to stochastic forcing by turbulent gas. We include the orbital dynamics of Keplerian disks, both in-plane epicycles and vertical oscillations. We obtain a new result for the diffusion of solids. The Schmidt number (ratio of gas to particle diffusivity) is Sc ≈ 1 + (Ωtstop), in terms of the particle stopping time tstop and th...

We have integrated carbon felt, a traditional fuel cell gas diffusion layer, with silicon micro fuel cells. To this end we used two silicon microfabrication procedures using reactive ion etching: formation of black silicon and sinking of flowfield. The former decreases electrical contact resistance to the diffusion layer, the latter serves to contain the reactant gases. The micro fuel cells, wh...

We describe the design, operation, and applications of two microfluidic devices that generate series of concentrations of oxygen, [O(2)], by on-chip gas mixing. Both devices are made of polydimethylsiloxane (PDMS) and have two layers of channels, the flow layer and the gas layer. By using in-situ measurements of [O(2)] with an oxygen-sensitive fluorescent dye, we show that gas diffusion through...

Output characteristics of fuel cells are affected by a large number of parameters such as geometry, dimensions, construction materials and conditions of supplying fluids. In this paper a mathematical model followed by a two-dimensional numerical approach has been presented to study the fuel cell parametrically. Effect of oxygen concentration at gas diffusion layer entrance, temperature and ...

Gas reservoirs with low permeability (k<0.1 mD) are among the unconventional reservoirs and are commonly termed as "Tight Gas Reservoirs". In conventional gas reservoirs that have high permeability, the flow of gas is basically controlled by the reservoir permeability and it is calculated using the Darcy equation. In these reservoirs, gas flow due to gas diffusion is ignored compared to Dar...

The permeability of the swimbladder to gas was measured as the conductance to oxygen in seven species of fish. The low over-all conductance resides in the low diffusion constant, K, of the middle layer of the wall (submucosa) while the outer and inner layers (tunica externa and mucosa) have diffusion constants similar to other vertebrate tissues. The low diffusion constant is due to a low diffu...

This paper presents a two-dimensional computational model of micro-structured cathodic electrodes featuring nano-porous gas diffusion media that increase the surface to volume ratio of the deposited catalyst layer. A key objective of the modeling effort is to elucidate the Knudsen diffusion within the nano-porous electrode. In addition, the model is non-isothermal and resolves the natural conve...

A novel approach to grow a 3D COF-320 membrane on a surface-modified porous α-Al2O3 substrate is developed. A compact and uniform COF-320 membrane with a layer thickness of ∼4 μm is obtained. This is the first reported 3D COF functional membrane fabricated successfully on a common porous α-Al2O3 ceramic support. The gas permeation results indicate that the gas transport behavior is mainly gover...

recently, special type of fuel cells has been developed that operates in a dead end mode. working in this condition, the dead-end fuel cell is supplied withhydrogen almost at the same rate of consumption. it is noteworthy to mention thatall of the water transport mechanisms have been considered in this simulation.water accumulation that is directly proportional to the cell current is of a great...