Porous media experimental results

Lee KY, Chrysikopoulos CV (2002) Dissolution of a well-defined trichloroethylene pool in saturated porous media experimental results and model simulations. Water Res 36 3911-3918... 

The theory of regular solutions applied to mixtures of aromatic sulfonate and polydispersed ethoxylated alkylphenols provides an understanding of how the adsorption and micellization properties of such systems in equilibrium in a porous medium, evolve as a function of their composition. Improvement of the adjustment with the experimental results presented would make necessary to take also in account the molar interactions of surfactants adsorbed simultaneously onto the solid surface. 

All these different mechanisms of mass transport through a porous medium can be studied experimentally and theoretically through classical models (Darcy s law, Knudsen diffusion, molecular dynamics, Stefan-Maxwell equations, dusty-gas model etc.) which can be coupled or not with the interactions or even reactions between the solid structure and the fluid elements. Another method for the analysis of the species motion inside a porous structure can be based on the observation that the motion occurs as a result of two or more elementary evolutions that are randomly connected. This is the stochastic way for the analysis of species motion inside a porous body. Some examples that will be analysed here by the stochastic method are the result of the particularisations of the cases presented with the development of stochastic models in Sections 4.4 and 4.5. 

In the scientific literature, we can find a large quantity of experimental results where the flow characterization inside a porous medium has shown that the value of the dispersion coefficient is not constant. Indeed, for the majority of porous structures the diffusion is frequently a function of the time or of the concentration of the diffusing species. As far as simple stochastic models cannot cover these situations, more complex models have been built to characterize these dependences. One of the first models that gives a response to this problem is recognized as the modd of motion with states having multiple vdodties. 

Core Floods. At present the strong coupling between droplet size and flow has major experimental consequences (1) flow experiments must be performed under steady-state conditions (since otherwise the results may be controlled by long-lived, uninterpretable transients) (2) in situ droplet sizes cannot be obtained from measurements on an injected or produced dispersion (because these can change at core faces and inside the core) and (3) care must be taken that pressure drops measured across porous media are not dominated by end effects. Likewise, since abrupt droplet size changes can occur inside a porous medium, if the flow appears to be independent of the injected droplet-size distribution, it is likely that a new distribution is quickly forming inside the medium (38). 

For the tortuous and irregular capillaries of porous media, it has been reported theoretically and experimentally that a minimum in the permeability of adsorbates at low pressures is not expected to appear. In our study of n-hexane in activated carbon, however, a minimum was consistently observed for n-hexane at a relative pressure of about 0.03, while benzene and CCI4 show a monotonically increasing behavior of the permeability versus pressure. Such an observation suggests that the existence of the minimum depends on the properties of permeating vapors as well as the porous medium. In this paper a permeation model is presented to describe the minimum with an introduction of a collision-reflection factor. Surface diffusion permeability is found to increase sharply at very low pressure, then decrease modestly with an increase in pressure. As a result, the appearance of a minimum in permeability was found to be controlled by the interplay between Knudsen diffusion and surface diffusion for each adsorbate at low pressures. 

In the near future, the development of the molecular simulation methods and the availability of results of comparison studies for a wide range of microporous sorbents should make the situation clearer However, these methods are always based on the same kind of experimental data a N2 adsorption isotherm at 77 K. These experimental conditions are very often far from those prevailing in the industrial applications. The use of a single adsorption isotherm within standard conditions could be considered as an advantage as it simplifies the experimental part of the characterization procedure. On the other hand, the possibility of using adsorption data in a wider temperature and pressure domain of conditions and for a large range of adsorbates should be helpful to prove or to invalidate the efficiency of the theoretical treatments. Besides, it would allow to adapt the complete characterization procedures and thus the choice of the experimental conditions in order to fit the final application in which the porous medium will be involved. 

Upon examining the experimental results given in Fig. 9.24, we note that except for the 8Id = 5.5 layer, we have q < q(8 = 8g(), that is, the two-phase region extends beyond the porous layer and into the plain medium. 

Consider a porous medium consisting of sand or some porous rock or glass beads or macaroni or cotton cloth contained in a pipe see Fig. 12.2. If we attach this pipe to the apparatus for the pressure-drop experiment shown in Fig. 6.1 and run exactly the same tests on it that we described there for a pipe, we find results of the same form as those shown in Fig. 6.2, except that the abrupt transitions region on Fig. 6.2 will be replaced with a smooth curve for a porous-medium flow. From these results we guess that the two end parts of the curve correspond to laminar and turbulent flows this is experimentally verifiable. I... 

The authors modeled the microchannel heat sink, subject to an impinging jet, as a porous medium. Based on their experimental results, they suggested correlatiOTis for the pressure drop across a microchannel heat sink subject to an impinging jet as well as its thermal resistance as follows ... 

The mole fractions of CH4 in the fuel channel exhaust are presented in Fig. 5.11 and the mole fractions of CH4 in the electrolyte channel exhaust are displayed in Fig. 5.12. For both cases DGM and MFM work well in predicting the experimental observations. However, for electrolyte exhaust the observations are best matched by MTPM and MMF predictions, and GMS predictions are in best agreement with experimental observations for fuel channel exhaust. Similar to the case of CO2 the concentration of CH4 in the fuel channel outlet increases with increasing flow rate, while the concentration decreases in the electrolyte channel outlet. All the CH4 present in the electrolyte exhaust results from the diffusion of CH4 across the porous medium from the fuel channel to the electrolyte channel. Due to the decreasing... 

Because surface tension and contact angle are two of the main parameters of the capillary pressure expression, capillary pressure curves are very sensitive to the state of the internal surface of the porous medium and apparently the experimental results under the same conditions can vary. 

The pores of a 2-mm-thick sintered silica (porosity 0.3) are filled with water at 25°C. At one side of the solid a potassium chloride solution (0.10 g mole/liter) is placed. Pure water flows past the other side. Experimental observation shows the potassium chloride flux to be 7.01 X 10 kg mole/sec. Based on this result, derive an appropriate equation to describe this system. (Hint Alter the diffusion equation to reflect the porous medium.)... 

---