Wetting criterion

The discussion presented above is valid whether absorption of a gas into a liquid or desorption of a gas from a liquid is carried out. If a vapor is absorbed into a liquid, the same considerations are valid. If stripping is implemented via vacuum in a nondispersive fashion, the pressure conditions for the two-phase system and the wetting criterion remain unchanged to ensure that the hydrophobic porous membrane remains nonwetted. If, however, the liquid phase exists inside the pores, then to achieve nondispersive operation, the gas-phase pressure should be equal to or greater than that of the liquid phase (Karoor and Sirkar, 1993). Vacuum stripping is not possible with liquid in the membrane pores, that is, wetted pores it is necessary to have a nonporous coating on the side of the membrane where the gas-liquid interface would have been loeated otherwise (Sirkar, 1992). 

An example where one metal melts before the densihcation process, is the formation of bronze from a 90 10 weight percentage mixture of copper and tin. The tin melts at a temperature of 505 K, and the liquid immediately wets the copper particles, leaving voids in the compact. The tin then diffuses into the copper particles, leaving further voids due to dre Kirkendall effect. The compact is therefore seen to swell before the hnal sintering temperature of 1080 K is reached. After a period of homogenization dictated by tire criterion above, the alloy shrinks on cooling to leave a net dilatation on alloy formation of about 1%. 

Good wetting is of course not a sufficient criterion for good contact adhesion because it takes no account of the factors that influence the mechanical loss factor, C, in Eq. 8, nor does it account for residual stress development during cure. But aside from these factors, one might inquire into the validity of the correlation between practical contact adhesion and VEa beyond 0° contact angle , i.e. can any distinction be made based on VEa between different adhesives, all of which perfectly wet the adherend ... 

After some early uncertainty in the literature about the nature of the pressure sensitive bond, Dahlquist [5,6] related modulus data to tack-temperature studies and observed that the compression modulus of the adhesive had to be less than about 3 X 10 dyne/cm (3 x lO Pa) before any adhesive tack was observed. This was explained as the highest modulus that still allowed the adhesive to be sufficiently compliant to wet out or come into molecular contact with the substrate and form dispersive bonds. As other investigators [7-9] accepted this requirement it was termed the Dahlquist Criterion . 

In water, the concentration of toxaphene considered safe for protection of freshwater life is conservatively estimated to lie between 0.008 and 0.013 pg/L for marine life, it is 0.07 pg/L. This is in sharp contrast to the current recommended drinking water criterion for human health protection of 5.0 to 8.8 pg/L. Similarly, residues in fish tissue in excess of 0.4 to 0.6 mg/kg wet weight may be hazardous to fish health and should be considered as presumptive evidence of significant environmental contamination, although fish may contain up to 5.0 mg/kg before they are considered hazardous to human consumers. Toxaphene criteria for human health protection — which range in various foods from 0.1 mg/kg for sunflower seeds to 7.0 mg/kg in meat, fats, and citrus fruits — also appear adequate to safeguard sensitive species of wildlife. 

Wet-weather processes are subject to high variability. A simple deterministic model result in terms of the impacts on the water quality is out of scope. From a modeling point of view, a stochastic description is a realistic solution for producing relevant results. Furthermore, an approach based on a historical rainfall series as model input is needed to establish extreme event statistics for a critical CSO impact that can be compared to a water quality criterion. In terms of CSO design including water quality, this approach is a key point. 

It is possible that the pores of wetted catalyst particles eire filled with liquid. Hence, by virtue of the low values of liquid diffusivities (ca. 10 cm s" ), the effectiveness factor will almost certainly be less than unity. A criterion for assessing the importance of mass transfer in the trickling liquid film has been suggested by Satterfield [40] who argued that if liquid film mass transport were important, the rate of reaction could be equated to the rate of mass transfer across the liquid film. For a spherical catalyst particle with diameter dp, the volume of the enveloping liquid fim is 7rdp /6 and the corresponding interfacial area for mass transfer is TTdn. Hence... 

In the construction of the wet oxidation unit, several areas of safety were considered. Of utmost importance was that of personal safety. Since this type of operation demands the use of high pressures and temperatures, operator contact with the high pressure vessels had to be limited. To accommodate this criterion, a barrier was constructed to shield the operator from any unforeseen releases from the reactor. This barrier was constructed from 1/4 inch steel and is desig ied in a manner that will fully contain any releases. This barrier is also equipped with two explosion vents to direct the force of any explosions away from the main walls and into a safe area. To further maximize personnel safety, all operator assisted controls are mounted on the outside of the unit. 

Blennow, A., Bay-Smidt, A. M., Leonhardt, R, Bandsholm, O., Madsen, H. M. (2003). Starch paste stickiness is a relevant native starch selection criterion for wet-end paper manufacturing. Starch, 55,381-389. 

To be an acceptable substitute for wet collectors and to satisfy the NIOSH criterion for acceptable methods, a sorbent material must have a demonstrated sorption capacity for the analyte that is adequate for sampling a reasonable volume of workplace air at an established rate. Typically, a sample volume of at least 12 L (1 h at 0.2 L/min) is desirable. 

No precise correlation is available between the immersion-compression test and results to be expected from pavements in the field. The test provides comparative guidance on water damage susceptibility. For the diabase aggregate, the Sulphlex-233 mixtures measured dry, and after immersign in the case of wet specimens, exceed the 300 psi (2.07 x 10 pascal) minimum compressive strength usually considered necessary for acceptable mixture performance in the field. Retained strengths generally fall below the 70 percent criterion considered acceptable for asphaltic mixtures. 

The end result of the surface chemistry of the reinforcement, the adsorbed material, topographical features, and epoxy composition is in the formation of the polymerized epoxy on the reinforcement surface. In order for this to happen, the fluid epoxy mixture must be brought into contact with the reinforcement surface, wetting must take place and energy added to aid the polymerization. The wetting of the reinforcement by the epoxy is a necessary criterion for optimum mechanical properties. 

One common and simple test to determine the cleanliness of glassware is to examine how well water wets the glass. Water will bead up on the walls of dirty glassware, but on clean glass walls, it sheets. This test by itself should not, however, be used as the sole criterion for clean glass. 

Note that good wetting is necessary for bond formation. However, it is not the sole criterion for a strong adhesive joint. Several other important parameters, as noted in the sections that follow, strongly affect the adhesive strength of epoxy systems. 

Expressed for 2 g (wet weight) sample intake and 100 mL final volume following the three sigma criterion. 

In ideal trickle flow reactors, all particles in the catalyst bed take part in the overall reactor performance, since each is surrounded (wetted) by the liquid phase that flows around it. Situations in which the liquid flows preferentially through a certain part of the bed, while the gas phase flows predominantly through another part, should be avoided [23]. In this case, part of the bed is not contacted by the liquid reactant at all and docs not contribute to the overall conversion. To avoid this maldistribution, Gierman [20] proposed the following criterion for the wetting number Wtx for co-current downflow operation ... 

This criterion establishes the maximum amount of material that can be vaporized with a falling-film vaporizer. Approximately 85 percent of the entering material can be vaporized in a single pass without destroying the film. If tube loadings below the terminal loading are attempted, the film will break and form rivulets. Part of the tube surface will not be wetted, and the result will be reduced heat transfer with possible increased fouling of the heat-transfer surface. 

The positive semi-initial spreading coefficient appears to be a necessary but insufficient condition for stability of films at all thicknesses (except for diluted adsorption layers). That is why this coefficient cannot be taken as a criterion of stability of wetting films as it has been proposed in [522]. On the other hand, the negative semi-initial spreading coefficient is not an obligatory condition for a heterocoalescence. The films can be unstable when s > 0, when se < 0 or se > 0. 

It is difficult to ascertain whether the poor performance observed in pilot-scale trickle-bed reactors is due either to ineffective catalyst wetting or to the axial dispersion effects, because both these effects are physically realistic and both occur under similar operating conditions (i.e., low liquid flow, large catalyst size, and shorter beds). It should be noted, however, that the criterion for removing the axial dispersion effect is available. A similar criterion for removing ineffective catalyst wetting is, however, presently not available. 

The cocurrent gas-liquid-solid fluidized beds considered are those in which the liquid supports and completely wets the solid. The gas flow thus constitutes a perturbation of a liquid fluidized bed. Unlike a gas-solid or a liquid-solid fluidized bed, a gas-liquid-solid fluidized bed may either contract or expand when gas bubbles are introduced into the bottom of the bed. Considerable work has been done on deriving the criteria for the bed contraction and expansion. The most up-to-date work on this subject is by Epstein.28 He derived the criterion for initial contraction and expansion of three-phase fluidized beds. He suggested that if the quantity... 

Accuracy is determined by the Identity of oxides from different sources. X-ray analysis is not a prime indicator because we are interested in the properties of the surface. A better criterion is the point of zero charge because it reflects the acidities and basicities of the surface groups (sec. 3.8). Moreover, the p.z.c. is affected by specific adsorption, even to the extent that it can be taken as a diagnostic of pristlnity. For Instance, when a commercial alumina (pristine p.z.c. > 9) has a p.z.c. of 6 this might be caused by the presence on the surface of substantial amounts of sllica(tes). intentionally added by the manufacturer to obtain certain dispersion or wetting characteristics. Apart from this, oxides from different sources may have different surface properties and different p.z.c. s. Synthetic and natural minerals may differ. Differences in the mode of preparation, particularly with respect to calcination, may show up as heating... 

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