Pressure gradient process

Capillary pressure gradients and Marongoni flow induce flow in porous media comprising glass beads or sand particles [40-42], Wetting and spreading processes are an important consideration in the development of inkjet inks and paper or transparency media [43] see the article by Marmur [44] for analysis of capillary penetration in this context. 

Because RPSA is appHed to gain maximum product rate from minimum adsorbent, single beds are the norm. In such cycles where the steps take only a few seconds, flows to and from the bed are discontinuous. Therefore, surge vessels are usuaHy used on feed and product streams to provide unintermpted flow. Some RPSA cycles incorporate delay steps unique to these processes. During these steps, the adsorbent bed is completely isolated and any pressure gradient is aHowed to dissipate (68). The UOP Polybed PSA system uses five to ten beds to maximize the recovery of the less selectively adsorbed component and to extend the process to larger capacities (69). 

The simplifying assumptions that make Tick s law useful for other processes are not vaHd for pei vaporation. The activity gradient across the membrane is far more important than the pressure gradient. Equation (22-110) is generally used to describe the pei vaporation process ... 

The physical process of melt ascent during two-phase flow models is typically based on the separation of melt and solid described by Darcy s Law modified for a buoyancy driving force. The melt velocity depends on the permeability and pressure gradients but the actual microscopic distribution of the melt (on grain boundaries or in veins) is left unspecified. The creation of disequilibria only requires movement of the fluid relative to the solid. 

While no system has been designed that will meet all of these characteristics, the ones that come closest are those that utilize coatings of semipermeable polymers on solid cores leading to release rates that are wholly or largely controlled by transport of water across the coatings in response to an osmotic pressure gradient. The reasons for this success are due, in large part, to the fundamental nature of the processes involved. 

Finding the pressure drop corresponding to a total mass flux Gm from this equation requires a stepwise procedure using physical property data from which the densities of both the gas phase and the mixture can be determined as a function of pressure. For example, if the upstream pressure P and the mass flux Gm are known, the equation is used to evaluate the pressure gradient at point 1 and hence the change in pressure AP over a finite length AL, and hence the pressure Px+i = Px — AP. The densities are then determined at pressure P1+i. And the process is repeated at successive increments until the end of the pipe is reached. 

Figure 1. Schematic illustration of factors influencing the production and migration of radon in soils and into buildings. Geochemical processes affect the radium concentration in the soil. The emanating fraction is principally dependent upon soil moisture (1 0) and the size distribution of the soil grains (d). Diffusion of radon through the soil is affected primarily by soil porosity ( ) and moisture content, while convective flow of radon-bearing soil gas depends mainly upon the air permeability (k) of the soil and the pressure gradient (VP) established by the building.

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