Gas pressure gradient

Burst Assumed external pressure gradient of saltwater = 0.465 psi/ft and formation pore (gas) pressure gradient = 0.65 psi/ft. Gas weight is neglected. Safety factor = 1.1. 

An external gas pressure gradient applied between anode and cathode sides of the fuel cell may be superimposed on the internal gradient in liquid pressure. This provides a means to control the water distribution in PEMs under fuel cell operation. This picture forms the basis for the hydraulic permeation model of membrane operation that has been proposed by Eikerling et al. This basic structural approach can be rationalized on the basis of the cluster network model. It can also be adapted to include the pertinent structural pictures of Gebel et and Schmidt-Rohr et al. ... 

The experimental data (dots) are reproduced very well within the framework of the hydraulic permeation model (solid lines). For the basic case with zero gas pressure gradient between cathode and anode sides, APe = 0, the model (solid line) predicts uniform water distribution and constant membrane resistance at )p < 1 A cm and a steep increase in R/R beyond this point. These trends are in excellent agreement with experimental data (open circles) for Nafion 112 in Figure 6.15. A finife positive gas pressure gradient, APs = P/ - P/ > 0, improves the internal humidification of fhe membrane, leading to more uniform water distribution and significantly reduced dependence of membrane resistance on X. The latter trends are consistent with the predictions of fhe hydraulic permeation model. 

Note. For gas permeability the partial gas pressure gradient across the film is 1 atm. For water vapour transmission the humidity gradient is 90%. a Increases with ethylene content. b Decreases with ethylene content. 

More attention was given to instability of operation. Generally, standpipes are devices used to convey particulate solids against an adverse gas pressure gradient with the aid of gravity. The standpipe must also function as a seal to prevent backflow of gas against the direction of motion of the particles. In certain circumstances, standpipes may malfunction, apparently undergoing a transition to a state in which there is much smaller pressure buildup within... 

The gas pressure gradient set up by gas-particle friction can be described by the modified Ergun equation (Ergun, 1952) and Kwauk equation (Kwauk, 1963), shown respectively as follows ... 

The key to implementing any corrective actions designed to reduce adverse flow-effects will be using a mathematical two-phase flow analysis to assess the effects on the bulks solids stresses and interstitial gas pressure. This analysis would need to use inputs such as key flow properties (permeability, compressibility) and equipment/process parameters (tableting rate, bin/hopper geometry, and gas pressure gradients) to assess the effect of the potential corrective actions outlined above. 

The external gas pressure gradient will, thus, be superimposed as a driving force of water flux on the internal pressure gradients that develop due to electroosmotic effect and capillary forces. Note that gas pressures in anode and cathode chambers can be controllably varied. 

To ensure that the dust molecules are motionless, = 0, a net external force is used to prevent them from moving in response to any gas pressure gradients [49] ... 

The sample holder should have as small a vapor volume as possible. A large vapor volume allows gas pressure gradients in the sample, may result in different reactions, and, it is claimed, may cause nonstoichiometric mass-losses. A large vapor volume will also make it more difficult to locate 7 and hence more difficult to compare results by different investigators. Also in this... 

The drill hole helps the discretization of the gas in its flow region in the coal seam. According toformula (1), the differential equation of the gas flow in the coal seam can be derived. Due to the gas pressure gradient around the drill hole, the coal seam gas always flows from where pressure is high to where pressure is low. That is, the gas will flow to the wall of the drill hole from a distance. The amount of gas emission per unit area q(m l(m s)) on the wall of the drill hole can be obtained by Darcy Law as follows ... 

When the manometric hole is sealed, with the accumulation of high pressure gas in the menometric room, the pressure gradient near the hole wall gets lower, the amount of gas emission per unit decreases as well. When the supplementary amount of gas in the menometric room Q equals to the gushing amount of gas in the coal seam hole section the gas pressure in the menometric room and in the coal seam stays in balance, and the gas pressure gradient near the hole wall is 0. That is,... 

It descends the stress gradient of coal around drill by using hydraulic flushing caused coal gas permeability increased by a large margin while release stress, the gas released and gas pressure gradient fell sharply, not eliminate the stress and gas condition aroused by... 

Wang, G., Cheng, W.M., Sun, L.L., 2013. Analysis of Influencing Factors for Coal Seam Gas Pressure and Gas Pressure Gradient. Safety In Coal Mines, 44(2) 152-156. 

Research quantitative model of gas pressure gradient and in-situ stress in complex tectonic outburst coal seam... 

THE GAS PRESSURE GRADIENT AND THE QUANTITATIVE MODEL OE IN-SITU STRESS... 

According to Darcy s law, the gas pressure gradient of coal seam is proportional to the gas seepage velocity(Wang Ji-ren 2005, Xu Xue-feng 2003, Sun Jing-lai 2009). Its expression is ... 

In the formula, is effective stress in the coal, under the conditions that coal quality, damage degree of coal, gas pressure and stress of surrounding rock, formula (1), (2), (3) are substituted in formula (4), then relational expression of gas pressure gradient and in-situ stress can be get ... 

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