Compressing capillary pressure

At low ij), the cmve is linear. At high values of < >, there is a critical value, where no fiirther shrinks e takes place, corresponding to liquid just filling the pores at the leatherhard point. This critical volume fraction, <, occurs when the mechanical properties of the particle network is sufficiently rigid to resist the compressive capillary pressure. The liquid expansion of a ceramic green body, a, is defined by... 

Let us consider one more physical phenomenon, which can influence upon PT sensitivity and efficiency. There is a process of liquid s penetration inside a capillary, physical nature of that is not obvious up to present time. Let us consider one-side-closed conical capillary immersed in a liquid. If a liquid wets capillary wall, it flows towards cannel s top due to capillary pressure pc. This process is very fast and capillary imbibition stage is going on until the liquid fills the channel up to the depth l , which corresponds the equality pcm = (Pc + Pa), where pa - atmospheric pressure and pcm - the pressure of compressed air blocked in the channel. 

If the solid in question is available only as a finely divided powder, it may be compressed into a porous plug so that the capillary pressure required to pass a nonwetting liquid can be measured [117]. If the porous plug can be regarded as a bundle of capillaries of average radius r, then from the Laplace equation (II-7) it follows that... 

Another condition that can impair venous return is pregnancy. As the uterus enlarges during gestation, it may cause compression of the veins draining the lower extremities. Once again, venous and capillary pressures are increased. Filtration is enhanced, reabsorption is inhibited, and edema develops in the lower extremities. 

As sfafed previously, fhe capillary pressure dafa, fhe overall pore disfribu-tion (when ocfane is fhe working fluid), and fhe hydrophilic pore distribution (when water is the working fluid) can be obfained through this technique. In addition, these measurements can be used with different compression pressures of fhe sample DL and wifh a wude range of temperatures inside the system [200,201]. For more information regarding this technique, please refer to fhe paper by Volfkovich ef al. [198]. 

Fairweather et al. [204] developed a microfluidic device and method to measure the capillary pressure as a function of fhe liquid water saturation for porous media wifh heferogeneous wetting properties during liquid and gas intrusions. In addition to being able to produce plots of capillary pressure as a function of liquid wafer safuration, their technique also allowed them to investigate both hydrophilic and hydrophobic pore volumes. This method is still in its early stages because the compression pressure and the temperatures were not controlled however, it can become a potential characterization technique that would permit further understanding of mass transport within the DL. 

Figure 8. Air—water capillary pressure curves for treated Toray TGP-H-120 (10 wt%) under compression (black markers) and uncompressed (white markers).21...

Figure 18. Advancing liquid water front with increasing capillary pressure through die initially air-saturated reconstructed GDL microstructure with 30% compression from the primary drainage simulation.

In stage 2 the pores are emptied. Though the capillary pressure is at its highest level, at the critical point the network may not be compressed further, and the pore liquid evaporates. Liquid is transported through films that cover partially empty pores and evaporates at the surface. The capillary forces reduce consequently. 

The dependence of the average excess pressure in foam (capillary pressure of bubbles) on its specific area is established by Derjaguin [105]. The mechanical work W done under isothermal compression (or decompression) of foam equals... 

Another dynamic factor affecting the rate of diffusion transfer, mentioned long ago by Gibbs [9], is the elasticity of the surfactant monolayers which decreases the capillary pressure in small bubbles during their compression and increases it in large bubbles during their expansion. This effect is most pronounced in bubbles whose adsorption layers contain insoluble surfactants. Analysis of the influence of this factor on diffusion transfer has been reported in [486], However, no experimental verification has been performed so far. 

As the partial pressure gradient moves into the green body, the pores empty accordingly. For this reason, the green body will not be completely dry when the bulk gas used for drying has a nonzero partial pressure of the solvent. Some liquid will remain in the smallest capillaries where the radius of curvature is sufficiently small. These filled capillaries will contribute to a compressive capillary force which holds the green body together. 

The above discussion is concerned with single bubble displacement. To obtain results analogous to Equations 6, 8, and 9 for bubble trains, it is necessary to account for changes in curvature at the bubble ends (in the Plateau border regions) due to the compression between adjacent bubbles. Referring to Figure 5(b), the contact radius Rc can be related to the capillary pressure Pc = Pi - Pi = P - P by... 

An original method involves quadrupole oscillations of drops K The drop (a) in a host liquid (P) is acoustically levitated. This can be achieved by creating a standing acoustic wave the time-averaged second order effect of this wave gives rise to an acoustic radiation force. This drives the drop up or down in p, depending on the compressibilities of the two fluids, till gravity and acoustic forces balance. From then onwards the free droplet is, also acoustically, driven into quadrupole shape oscillations that are opposed by the capillary pressure. From the resonance frequency the interfacial tension can be computed. The authors describe the instrumentation and present some results for a number of oil-water interfaces. 

The contrasting structure of the plates and the separators is also relevant to the functioning of the battery. For example, the capillary pressures dictate that electrolyte fills the plates preferentially. This preferential filling appears to be the ideal situation since it can best support the electrochemical reaction, i.e., it leaves the separator partially saturated so that movement of electrolyte can provide pathways for gas transport. If, however, the overall saturation is too low or there is excessive loss of water, the separator will dry out and give rise to an increase in the internal resistance of the battery and the possibility of thermal runaway. An increase in internal resistance, and consequent low service-life, can also result if the compression between separators and battery plates relaxes over a period of time. Overcompression may cause fibres to fracture with a loss of resilience, i.e., the separators lose the ability to return to original thickness after a high pressure is applied and... 

In most unsaturated rocks and soils, elastic properties and plastic flow depend on the capillary pressure which is related to water saturation degree through water retention curve (Fredlund and Rahardjo 1993). In this work, for simplicity, we neglect the variation of elastic constants with capillary pressure. However, we intend to account for the influence of capillary pressure on plastic behaviour of argillites. Only a small number of triaxial compression tests with different water saturation degrees are available. We can only provide a first approximation of such a influence. We consider that the failure parameter A (see Equation 13) linearly increases with capillary pressure ... 

On Figure 4, we present simulations of triaxial compression tests performed with different water saturation degrees. Even if constant elastic parameters have been used, there is a qualitatively good agreement between simulations and data. Mechanical strength of material increases when saturation degree decreases due to effect of capillary pressure. 

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