Silicone based oil is heated in the boiler of the diffusion pump and the vaporized oil rises in the central tower and streams out of directional flutes directed downward in the pump throat. This allows air molecules to dissolve in the gaseous oil (gas dissolved in gas). As the oil-air mixture cools (due to water cooling coils wrapped around the pump throat) the oil condenses and returns to liqu...

Vapor phase lubrication is considered one of the most likely means of lubricating MEMS devices with replenishable solid films. Since gas phase diffusion is the primary means of vapor lubricant transport into the long, narrow channels of MEMS devices, it is necessary to determine that this is sufficient to replenish lubricant films worn at high rates. The diffusion of vapor phase lubricant into ...

We consider element diffusion during the linear growth of structure in the intergalactic medium (IGM) before the redshift of reionization. The elements produced during big bang nucleosynthesis (such as D, 4He or 7Li) condensed in collapsing regions more readily than hydrogen. Diffusion was most effective when the IGM was neutral since the collisional cross–section between neutral species is sma...

Recently it has been suggested that dislocations, generated by radiation damage, may increase the rate of fission gas diffusion from the fuel grains, an affect which is at present not incorporated into fuel performance codes. Therefore, we perform molecular dynamics simulations employing empirical potentials to investigate the diffusion of Xe atoms around edge dislocations in UO2 to establish t...

2014 The general results recently obtained for the Boltzmann collision term in a gas of atomic hydrogen are applied to the study of longitudinal spin diffusion in high magnetic fields. This phenomenon can be described as a diffusion of concentration in a four component reactive mixture (the reaction being here the electronic transfer between nuclei). A numerical discussion of all the coefficien...

We have established methods to evaluate key properties that are needed to commercialize polyelectrolyte membranes for fuel cell electric vehicles such as water diffusion, gas permeability, and mechanical strength. These methods are based on coarse-graining models. For calculating water diffusion and gas permeability through the membranes, the dissipative particle dynamics–Monte Carlo approach w...

We consider the Maxwell-Stefan model of diffusion in a multicomponent gaseous mixture. After focusing on the main differences with the Fickian diffusion model, we study the equations governing a three-component gas mixture. Mostly in the case of a tridiagonal diffusion matrix, we provide a qualitative and quantitative mathematical analysis of the model. We develop moreover a standard explicit n...

Experiments were conducted to measure the transportability of radon gas through common concrete samples which were characterized by their mix proportions, dimensions, porosity, air permeability and radon gas diffusion coefficient. Several innovative test systems and methods were designed, fabricated and calibrated to accurately measure these radon gas transport characteristics for concrete and ...

Analytical models were developed that simulate stable isotope ratios of volatile organic compounds (VOCs) near a point source contamination in the unsaturated zone. The models describe diffusive transport of VOCs, biodegradation and source ageing. The mass transport is governed by Fick's law for diffusion. The equation for reactive transport of VOCs in the soil gas phase was solved for differen...

Transport properties of impurities immersed in a granular gas undergoing homogenous cooling state are studied. The results are obtained from the Boltzmann-Lorentz kinetic equation for inelastic Maxwell models in d dimensions. The kinetic equation is solved by means of the Chapman-Enskog method up to first order in the density gradient of impurities. The mass and heat fluxes associated with impu...