Time of contact

Figure Bl.12.10. CP data from the two carbons in glycine as a fiinction of contact time. The signal for short contact times is shown in the inset where the effect of the different Tjs values can be clearly seen.

SolubiHty of carbon dioxide in ethanolamines is affected by temperature, amine solution strength, and carbon dioxide partial pressure. Information on the performance of amines is available in the Hterature and from amine manufacturers. Values for the solubiHty of carbon dioxide and hydrogen sulfide mixtures in monoethanolamine and for the solubiHty of carbon dioxide in diethanolamine are given (36,37). SolubiHty of carbon dioxide in monoethanolamine is provided (38). The effects of catalysts have been studied to improve the activity of amines and provide absorption data for carbon dioxide in both mono- and diethanolamine solutions with and without sodium arsenite as a catalyst (39). Absorption kinetics over a range of contact times for carbon dioxide in monoethanolamine have also been investigated (40). 

Between 1 s and 1 min specific contact time, conduction heat-transfer performance decreases theoretically as the 0.29 power of contact time. This is consistent with empirical data from several forms of indirect-heat dryers which show performance variation as the 0.4 power of rotational speed (21). In agitator-stirred and rotating indirect-heat dryers, specific contact time can be related to rotational speed provided that speed does not affect the physical properties of the material. To describe the mixing efficiency of various devices, the concept of a mixing parameter is employed. An ideal mixer has a parameter of 1. 

Mangipudi et al. [63,88] reported some initial measurements of adhesion strength between semicrystalline PE surfaces. These measurements were done using the SFA as a function of contact time. Interestingly, these data (see Fig. 22) show that the normalized pull-off energy, a measure of intrinsic adhesion strength is increased with time of contact. They suggested the amorphous domains in PE could interdiffuse across the interface and thereby increase the adhesion of the interface. Falsafi et al. [37] also used the JKR technique to study the effect of composition on the adhesion of elastomeric acrylic pressure-sensitive adhesives. The model PSA they used was a crosslinked network of random copolymers of acrylates and acrylic acid, with an acrylic acid content between 2 and 10%. 

Fig. 22. Nomialized pull-off energy measured for polyethylene-polyethylene contact measured using the SFA. (a) P versus rate of crack propagation for PE-PE contact. Change in the rate of separation does not seem to affect the measured pull-off force, (b) Normalized pull-off energy, Pn as a function of contact time for PE-PE contact. At shorter contact times, P does not significantly depend on contact time. However, as the surfaces remain in contact for long times, the pull-off energy increases with time. In seinicrystalline PE, the crystalline domains act as physical crosslinks for the relatively mobile amorphous domains. These amorphous domains can interdiffuse across the interface and thereby increase the adhesion of the interface. This time dependence of the adhesion strength is different from viscoelastic behavior in the sense that it is independent of rate of crack propagation.

The effectiveness of disinfection increases with the amount of contact time available. 

Hypochlorous acid and hypochlorite ion are known as free available chlorine. The chloramines are known as combined available chlorine and are slower than free chlorine in killing microorganisms. For identical conditions of contact time, temperature, and pH in the range of 6 to 8, it takes at least 25 times more combined available chlorine to produce the same germicidal efficiency. The difference in potency between chloramines and HOCl can be explained by the difference in their oxidation potentials, assuming the action of chloramine is of an electrochemical nature rather than one of diffusion, as seems to be the case for HOCl. 

Where feed lines have short pipe runs, where hot wells or FW tanks are of small volume, or when FW is too cold, there often is insufficient time for full DO scavenging to take place, even when using catalyzed scavengers. The inevitable result of this lack of contact time is the formation of oxygen-induced corrosion products, which by various secondary mechanisms may settle out to form permanent deposits within the boiler system. These deposits may develop in several forms (e.g., where DO removal is particularly poor, they often appear as reddish tubercles of hematite covering sites where pitting corrosion is active). Active pitting corrosion combined with the presence of waterside deposits ultimately may lead to tube failure in a boiler or other item of system equipment and result in a system shutdown. 

Figure 4. EDA synthesis on H-EDTA-MOR (Si/Al=6.1) as a function of contact time (A) and as a function of partial pressure of NH3.

Walter et al. studied the flow distribution in simple multichannel geometries by means of the finite-element method [112]. In order to reduce the computational effort, a 2-D model was set up to mimic the 3-D multichannel geometry. Even at a comparatively small Reynolds number of 30 they found recirculation zones in the flow distribution chamber and corresponding deviations from the mean flow rate inside the channels of about 20%. They also investigated the influence of contact time variation on a simple two-step reaction. 

OS 94][R 13][P 74]ForadmixtureofsampleswifhvaryingconcentrationsofCo(ll) and Cu(II), the respective changes in the Co(ll) chelate complex concentration as a function of contact time were optically derived [28]. Analysis was performed in the reaction/extraction area and also in the decomposition/removal area (Figure 4.102). As expected, more complex is formed in the reaction/extraction area with increasing contact time. Also, more complex results when increasing the Co(ll) concentration at constant Cu(ll) concentration. This proves that mass transfer is efficient (as high concentrations can also be handled) and that no interference from other analytes falsifies the measurement. As a result, calibration curves were derived. 

The dissociation coefficient (KJ of the hybrids were determined to be 0.002 and 0.9 pg/ml, for GFP/SBA-15 and GFP/Aerosil , respectively, indicating that the interaction of GFP towards SBA-15 was very strong whereas towards Aerosil extremely weak [5], Concerning the rate of adsorption for the hybrid GFP/SBA-15, the saturation level was very fast and, for an initial concentration of 2.5 pg/ml of GFP in buffer solution, it was attained after 10 min of contacting time (Fig. 3). 

Fig. 11 Plot of the 13C signal intensity as a function of contact time for two distinct methyl resonances of two polymorphic forms of a developmental drug substance.

As was shown previously, reduction of contact time and specific surface may be helpful in lowering sorption losses, and acidification with strong acid will generally prevent the problems of losses by sorption. However, it must be emphasised that the use of acids may drastically change the initial composition of aqueous samples, making unambiguous interpretation of the analytical results cumbersome or even impossible [55]. 

A notable aspect of this equation is that L appears within it as prominently as the rate constant k+ or the groundwater velocity vx, indicating the balance between the effects of reaction and transport depends on the scale at which it is observed. Transport might control fluid composition where unreacted water enters the aquifer, in the immediate vicinity of the inlet. The small scale of observation L would lead to a small Damkohler number, reflecting the lack of contact time there between fluid and aquifer. Observed in its entirety, on the other hand, the aquifer might be reaction controlled, if the fluid within it has sufficient time to react toward equilibrium. In this case, L and hence Da take on larger values than they do near the inlet. 

Figure 20.5 shows the effect of contact time and percentage adsorption oil-grease on the removal by thermally activated illite. 

Various adsorption parameters for the effective removal of Pb + and ions by using new synthesized resin as an adsorbent from aqueous solutions were studied and optimized. Time-dependent behavior of Pb + and ions adsorption was measured by varying the equilibrium time between in the range of 30-300 min. The percentage adsorption of Pb + plotted in Fig. 26.2 as a function of contact time... 

Time-depended behavior of Cu + ion adsorption was measured by varying the equilibrium time between in the range of 0.5-72 h. The percentage adsorption of Cu + ions plotted in Fig. 28.2 as a function of contact time. The percentage adsorption of Cu + indicates that the equilibrium between the Cu + ions and sumac leaves was attained 4 h. Therefore, 4 h stirring time was found to be appropriate for maximum adsorption and was used in all subsequent measurement. The effect of temperature and pH the adsorption equilibrium of Cu + on sumac leaves was investigated by varying the solution temperature from 283 to 303 and pH from 6 to 10. The results are presented in Fig. 28.3. The results indicated that the best adsorption results were obtained at pH 8 at 293 K. 

Fig. 1. Dehydration of cyclohexanol over pure alumina (P) at 410°. Influence of contact time.

Fig. 3. Distribution of butene as a function of contact time. 2-ButanoI over AljO, (from isopropoxide) at 350°.

In order to verify if the color and COD abatement from the solution was due to degradation by Fenton process rather than by an adsorption process, some experiments were repeated for an aqueous solution consisting of 100 ml 50 mM Na2S04 + 0.06 mM RB5 + required amount of catalyst, pH 2.8 and room temperature. Hydrogen peroxide was not included to avoid the Fenton chemistry. Figure 17 shows the absorbance spectra for (a) the initial solution, (b) after 180 minutes of contact time (catalyst C1+ BR5) without H2O2, and (c) in the presence of H2O2 after 180 minutes of Fenton process. 

Fig. 16.15 Phosphate adsorption curves of three low moor soils with different goethite content as a function of contact time (1 -238 h) (Schwertmann Schieck, 1980 with permission).

If wetting is instantaneous and the instantaneous wetting load at initial time is negligible, then the autohesive bond fracture stress, cr, is proportional to the fourth root of contact time and the fracture energy, GIC, is proportional to the square root of contact time as shown in the following equations ... 

In 1951,Danckwerts [4] proposed the surface renewal model as an extension ofthe penetration model. Instead of assuming a fixed contact time for all fluid elements, Danckwerts assumed a wide distribution of contact time, from zero to infinity, and supposed that the chance of an element ofthe surface being replaced with fresh liquid was independent of the length of time for which it has been exposed. Then, it was shown, theoretically, that the averaged mass transfer coefficient at the interface is given as... 

Figure 6. Distribution coefficients as functions of contact time and surface to mass ratios for Cs, Sr, and Am on granite (25°C, Aq os)...

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