Ideally wetting liquid

Fig. 10.6 Model sketches depicting the influence of surface roughness on the approach of particles to each other (left) and wetting (liquid bridge formation, right). The cross-hatched area is the actual bridge, a represents the mean distance between the particles, the outlines of the ideal particles (averaging out roughness), and the theoretical bridge contours assuming perfect wetting...

For a drop of liquid in equilibrium on a solid surface. Young s equation relates interfacial tensions at the solid/vapor interface yi, Uquid/vapor interface 72, and solid/liquid interface Y12, with the contact angle 0, which is a measure of the degree of wetting and takes a value of zero for ideal wetting... 

If we consider the typical example of a catalytic porous asymmetric membrane constituted by a thin catalytic layer supported by a macroporous substrate and a wetting liquid phase on the support side and a gas phase on the small pore catalytic side, the liquid will easily fill the pores of both the support and the porous catalytic layer. In order to move the gas-liquid interface from the support towards the catalytic porous layer, a pressure difference of the gas phase has to overcome the capillary pressure of the support. For the same reason, the position of the interface between the two fluid phases inside the porous catalytic layer will depend on the quaUty of the catalytic layer and on the strict control of the pressure difference between the two membrane compartments. In membrane contactors, usually the condition of gas-phase filled pore is preferred in order to reduce the overall mass transfer resistance across the membrane. In a catalytic membrane, both reactants in the two fluid phases need to reach the catalytic sites in the pore and therefore an ideal situation wherein the interface between the phases is very close to the catalytic sites is to be preferred in order to achieve the maximum reactant concentration in the reaction zone. This situation can be approximated by using a wetting liquid, a thin catalytic layer and fluid-fluid... 

In terms of liquid water saturation and water management in the CCL, the bimodal 5-distribution leads to a three-state model. The three states that any REV could attain are the dry state ( 0, water-free system), the ideally wetted state (5, =, primary pores are completely water-filled while secondary pores are... 

Figure 8.15. Plot of cell potential vs. fuel cell current density, (/o), indicating the effect of liquid water accumulation in the CCL on performance (soUd hne). The interplay of liquid water accumulation in pores and impeded oxygen transport causes the transition from the ideally wetted state to the fully saturated state (dotted tines), as indicated [51]. (Reprinted from Electrochimica Acta, 53.13, Liu J, Eikerting M. Model of cathode catalyst layers for polymer electrolyte fuel cells The role of porous structure and water accumulation, 4435— 46, 2008, with permission from Elsevier.)...

Upon increasing the current density generated by the fuel cell, a transition between two principal states of operation occurs, as illustrated in Figure 8.15. The ideally wetted state at low current densities exhibits levels of liquid water... 

For an ideal Newtonian liquid, the viscosity is a constant, independent of the shear rate (V). A pseudoplastic liquid exhibits a decreasing viscosity with increasing shear rate, where as a dilatant liquid shows an increasing viscosity with increasing shear rate (Fig. 6.3). Most polymer melts show pseudoplasticity. Wet beach sand is an example of a dilatant fluid. 

In the case of ideal wetting (this means that the contact angle among the solid, immersional liquid, and vapour of this immersional liquid = 0), the final state is... 

A second ideal model for adhesion is that of a liquid wetting two plates, forming a circular meniscus, as illustrated in Fig. XII-13. Here a Laplace pressure P = 2yz.A (h ws the plates together and, for a given volume of liquid. 

Carbon disulfide [75-15-0] is a clear colorless liquid that boils at 46°C, and should ideally be free of hydrogen sulfide and carbonyl sulfide. The reaction with alkaU cellulose is carried out either in a few large cylindrical vessels known as wet chums, or in many smaller hexagonal vessels known as dry chums. In the fully continuous viscose process, a Continuous Belt Xanthator, first developed by Du Pont, is used (15). 

The phenomenon of wetting of a solid by a liquid depends on the surfaces and interfacial energies. When a liquid droplet is in contact with an ideally smooth solid surface, as shown schematically in Fig. 9, according to the Young s equation [72], the contact angle (6) of the liquid is given by... 

In this case, Ptot is the measured pressure. The partial pressure of water vapor, Ph2o, is equal to the vapor pressure of liquid water. It has a fixed value at a given temperature (see Appendix 1). The partial pressure of hydrogen, PH2, can be calculated by subtraction. The number of moles of hydrogen in the wet gas, h2, can then be determined using the ideal gas law. 

For the flow of steam, a highly non-ideal gas, it is necessary to apply a correction to the calculated flowrate, the magnitude of which depends on whether the steam is saturated, wet or superheated. Correction charts are given by Lyle<5) who also quotes a useful approximation16 — that a steam meter registers 1 per cent low for every 2 per cent of liquid water in the steam, and 1 per cent high for every 8 per cent of superheat. 

For practical purposes, if the contact angle is greater than 90° the liquid is said not to wet the solid (if the liquid is water one speaks of a hydrophobic surface) in such a case drops of liquids tend to move about easily and not to enter capillary pores. If 8 = 0, (ideal perfect wettability) Eq. (A.4.3) no longer holds and a spreading coefficient, Sls(V). reflects the imbalance of surface free energies. 

Mercury is the only metal that is in a liquid state at room temperatures and remains liquid at temperatures well below the freezing temperature of water. Mercury is a noncombustible, heavy, silvery-colored metal that evenly expands and contracts with temperature and does not wet or stick to glass, which makes it ideal as a liquid for thermometers. Mercury is slightly volatile and will give off toxic fumes, especially if heated. Its has a unique melting point of —38.83°C, a boiling point of 3,56.73°C, and a density of 13.5336 g/cm. ... 

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