Prewetting

Nicolaides D and Evans R 1989 Nature of the prewetting critical-point Phys. Rev.L 63 778-81... 

In all the above mentioned processes of coffee decaffeination, changes occur that affect the roast flavor development. These changes are caused by the prewetting step, the effects of extended (four hours plus) exposure at elevated temperature as required to economically extract the caffeine from whole green beans, and the post-decaffeination drying step. 

Carbon should be prewetted prior to being placed in the test columns. Backwashing the carbon at low rates (2.5 m/hr) does not remove the air. Rates that would expand the bed 50 percent or 15-30 m/hr, are required. The liquid used for prewetting can either be water, if it is compatible with the liquid to be treated, or a batch of the liquid to be treated which has been purified previously. There are three types of carbon systems (1) fixed beds, (2) pulse beds, and (3) fluidized beds, and these can be used singly, in parallel, or in combination. The majority of systems are either fixed or pulse beds. The two basic types of adsorbers which can be designed to operate under pressure or at atmospheric pressure are the moving or pulse bed and the fixed bed. Either can be operated as packed or expanded beds. 

Since the prewetting transition may occur only for weakly attractive surfaces [146], we must choose an appropriate value for the parameter This value has been set as follows e = 3 /3/2 j = 6. This corresponds to a relative strength of the fluid-fluid and fluid-surface potential minima close to that for Ar in contact with sohd carbon dioxide [147]. The second parameter in Eq. (144), zq, was set to 0.8[Pg.219]

We observe that association leads to pronounced differences in the behavior of the system. In particular, we find that for the thick film the increase of the association energy leads to the increase of the height of the first local density peak. In contrast, the height of the local density maximum decreases at the region of small adsorption (below the prewetting transition). One can say that for increasing association energy the film structure becomes more ordered and its layered structure is more visible. 

Fig. 17 shows the adsorption isotherms of all (undimerized and dimerized) particles. Except for a very fast increase of adsorption connected with filling of the first adlayer, the adsorption isotherm for the system A3 is quite smooth. The step at p/k T 0.28 corresponds to building up of the multilayer structure. The most significant change in the shape of the adsorption isotherm for the system 10, in comparison with the system A3, is the presence of a jump discontinuity at p/k T = 0.0099. Inspection of the density profiles attributes this jump to the prewetting transition in the... 

The mean field treatment of such a model has been presented by Forgacs et al. [172]. They have considered the particular problem of the effects of surface heterogeneity on the order of wetting transition. Using the replica trick and assuming a Gaussian distribution of 8 Vq with the variance A (A/kT < 1), they found that the prewetting transition critical point is a function of A and... 

Prewetting of powders or fibrous solids. This extends to wet sweeping (if vacuum cleaning is impractical). 

TLC plates coated with the layer of polar adsorbent should be prewetted with a nonpolar solvent, such as benzene or n-heptane (n-hexane), to prevent deactivation of the adsorbent surface and to avoid glue up as a result of the penetration of the pores by lipid molecules and other impurities (i.e., wax). 

Figure 11.1a [1] shows a schematic representation of a micropreparative thin-layer chromatogram obtained on a 0.5-mm Florisil (magnesium silicate) layer prewetted with benzene of a crude extract, i.e., containing coextracted plant oil obtained from Heracleum moelendorfi fruit. The initial band of extract was washed with benzene and then separated by continuous development with ethyl acetate in benzene [1]. As seen from the fraction analysis presented in Figure 11.1b, small quantities of pure bergapten and xanthotoxin can be isolated in this maimer. 

Errington, J. R., Prewetting transitions for a model argon on solid carbon dioxide system, Langmuir 2004, 20, 3798-3804... 

Prewetting Transitions in Confined Fluids using Transition Matrix Methods... 

By tuning /. to obtain a bimodal particle number distribution, it was possible to locate the point of coexistence between saturated thin and thick films on the adsorbing surface. The prewetting coexistence curve was then obtained through the application of this procedure at each simulation temperature. 

Get some of your eluent and prewet the adsorbant somewhat. For about 10 g of adsorbant, start with 3 - 5 g of the liquid eluent. (Oh. Did anyone ever tell you, you can weigh liquids directly, just like solids ) Now add the eluent to the adsorbant and mix like mad. You can see the advantage of a screw-cap bottle over an open beaker. The powder can t fly out of a closed bottle. Do not add too much eluent You only want to precondition the adsorbant so that you don t get bubbling in the column from the heat of hydration released when you eventually run the experiment. 

Prevetol A4, biocide for antifouling coatings, 7.T56 Prewetting, 22 279 Priceite (pandermite), 4 133t Prices/pricing. See also Cost entries Economics... 

The pigments are incorporated into the resins before crosslinking to ensure homogeneous coloration. This can be done in the molten resin, for example in a kneader at about 90°C, or in dissolved or liquid resins by the liquid resin method. Ball mills are normally used for coloring prewetted powder molding compounds that have not yet been cured. 

Filtration of the dissolution sample aliquot is usually needed prior to quantitation. Filtration of the dissolution samples is usually necessary to prevent undissolved drug particles from entering the analytical sample and dissolving further. Also, filtration removes insoluble excipients that may otherwise cause a high background or turbidity. Prewetting of the filter with the medium is usually necessary. Filters can be in-line, at the end of the sampling probe, or both. The... 

Open the capsule and sprinkle the entire contents over approximately 10 ml of water and flush with swirling through a prewetted 16 French gastrostomy tube fitted with funnel at the port end. Additional aliquots of water are used to transfer all pellets and to flush the tube. Do not attempt the administration of pellets through a nasogastric tube. 

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