Wetting cycle

Fig, 6.17. Overall efficiency and specific work of dry and wet cycles compared. 

To this figure, some of the calculations carried out by various authors for wet cycles have been added RWI and HAT [9] REVAP [10] CHAT [11] TOPHAT [12],... 

In summary, all these wet cycles may be expected to deliver higher thermal efficiencies than their original dry equivalents, at higher optimum pressure ratios. The specific work quantities will also increase, depending on the amount of water injected. 

The general thermodynamic conclusions given above are confirmed by more detailed parametric studies which have been made by several authors of various wet cycles. 

Figure 3. Hexadecane/water/glass wetting cycle exhibiting water-wetting behavior. (Reproduced with permission from Teeters, D. Wilson, J. F. Andersen, M. A. Thomas, D. C. J. Colloid Interface Sci., 1988, 126 in press. Copyright 1988 Academic Press.)...

Figure 4. Hexadecane/water/PTFE wetting cycle showing oil-wet-ting behavior.

The computer interface system lends itself well to the determination of interfacial tension and contact angles using Equation 3 and the technique described by Pike and Thakkar for Wilhelmy plate type experiments (20). Contact angles for crude oil/brine systems using the dynamic Wilhelmy plate technique have been determined by this technique and all three of the wetting cycles described above have been observed in various crude oil/brine systems (21) (Teeters, D. Wilson, J. F. Andersen, M. A. Thomas, D. C. J. Colloid Interface Sci., 1988, 126, in press). The dynamic Wilhelmy plate device also addresses other aspects of wetting behavior pertinent to petroleum reservoirs. 

Far from a wellbore, the velocity of reservoir fluids is about one linear foot per day. Near a wellbore, the velocity can increase one-hundred fold. A static or quasi-static test such as the sessile drop (contact angle) test may not represent the dynamic behavior of the fluids in the field. The dynamic Wilhelmy device gives results which are comparable in interface velocity to the field displacement rate. The interface in the Wilhelmy test described here moved at a steady rate of 0.127 mm/sec or 36 ft/day. The wetting cycle for a hybrid-wetting crude oil system was not affected by moving at a rate less than 1 ft/day. 

Some crude oils contain components which can oxidize and change wettability (12, 25) so tests on reservoir oil samples must be performed in an oxygen-free environment. Exposure to air had a marked effect on the wetting cycle of one crude oil discussed below. 

Figure 5. Hexadecane-oleic acid /water/glass wetting cycle with hybrid-wetting behavior.

Figure 7. Wetting cycles of crude oil SS1473 tested in an open beaker. (Reproduced with permission from ref. 21. Copyright 1988 Society of Petroleum Engineers.)...

This study demonstrated two aspects of measurement of wettability of crude oils. Exposure to air can cause changes in the wetting cycle. This was not true of normal paraffins such as hexadecane, which yielded stable wetting cycles for days and weeks when exposed to air. Equilibration of the crude oil/brine/solid system also caused changes in the wetting behavior. From this study it is not clear whether the changes were due to equilibration of the oil and brine phases or the aging of the solid in the oil phase. It is likely that both affect the measurement. 

The wetting behavior of liquid/liquid/solid systems is not only dependent on the two liquid phases, but upon the interaction of the solid surface with these liquids (see Equation 1). An example is in the wetting cycles for glass and PTFE in a hexadecane/water system. 

A wetting cycle for a glass slide in a hexadecane/water system has the typical water-wetting cycle shown previously in Figure 3. 

Figure 4 shows the data for PTFE used as the solid phase with the same liquid/liquid system where an oil-wetting cycle is observed. When wetting cycles for plates of the minerals dolomite and marble were obtained for the hexadecane/water system, hybrid wetting cycles such as those shown in Figure 5 were seen. 

Plates of glass, PTFE, dolomite and marble were used. Dolomite and marble were chosen because they represent minerals found in oil reservoirs. Glass and PTFE were investigated because they represent high and low surface energy solids respectively and are good model systems for data comparisons. Liquid/solid wetting cycles were obtained for each of the solids in the liquids listed in Table III. 

A combination of SIPS with the stabilising and synthesis-favouring properties of clay minerals was studied by Rode et al. (1999) in experiments involving dry/wet cycles. The simultaneous use of both SIPS and clay minerals as catalytically active surfaces led to peptides up to and including the hexamer (Gly)6. The question as to whether this technique fulfils prebiotic conditions can (within certain limitations) be answered positively, since periodic evaporation phases in limited areas (lagoons, ponds) are conceivable. The container material could have consisted of clay minerals. Further progress in the area of peptide synthesis under conditions which could have been present on the primeval Earth can be expected. 

CoAF catalysts (Fig. 1) exhibited good NO reduction activity in the range 350-600°C, yielding N2, C02 and H20 as the main products, with a maximum NOx dry conversion of 20% and about 40%, respectively, on Co2.5AF at 550°C and Co4.2AF at 500°C. Under dry-wet cycles (Ciambelli et al., 2007) CoAF catalysts showed a progressive decrease of catalytic activity, which was not recovered in the subsequent dry tests. 

Figure 2. (a) NOx (full symbols) and CH4 (void symbols) conversions on Ag3.7Co2.6AF with dry feed and (b) NOx conversion on Ag2.7Co2.8AF in dry-wet cycles... 

However, a loss in catalytic activity is generated during dry-wet cycles, corresponding to a decrease in Co2 site occupancy and in a relevant occupation in Ag2. In this position Ag+, half-way between Co2 and Co2a, hinders or interferes with Co migration to the Co2a active sites. 

Denef K, Six J, Bossuyt H, Frey SD, Elliott ET, Merckx R, Paustian K (2001) Influence of dry-wet cycles on the interrelationship between aggregate, particulate organic matter, and microbial community dynamics. Soil Biol Biochem 33 1599-1611... 

Accelerated exposure equipment may also be used to test for weatherfastness in plastic materials [106], The natural destructive agents inherent in weather are approximated by filtering the radiation emitted by the xenon arc lamp and by spraying the sample with water under standardized conditions [106], Test programs are designed to relate to actual outdoor exposure to rain and humidity. In a standard program, a 3 minute wet cycle typically alternates with a 17 minute dry period. Weatherfastness tests are carried out and evaluated like lightfastness tests the black panel temperature and other parameters are the same in both procedures. 

The success of these model experiments led Bonner and coworkers to propose a mechanism involving repetitive cyclic sequences of partial polymerization followed by partial depolymerizaton in which the latter is caused by hydrolysis. Thus, this process is driven by environmental dry and wet cycles that could ultimately have led to homochiral polypeptides on early Earth. [97] Brach and Spach [95] have also proposed a mechanism involving partial hydrolysis for the enantiomeric enrichment of polypeptides having (3-sheet secondary structures. 

Ahmed Kabir etal. (1992) treated wood with DMDHEU as well as DMDHEU combined with a vinyl polymer, and determined the dimensional stability of the wood. Methane sulphonic acid was used as a catalyst in both cases. DMDHEU treatment resulted in a 50 % reduction in radial swelling following immersion in water for 100 minutes, with the combined treatment being snperior. However, the ASE (one cycle) of DMDHEU treated wood (30%) was snperior to that fonnd for the combined treatment (17%). DMDHEU appeared to be stable to hydrolysis over a number of wetting cycles. When DMDHEU-treated samples were exposed in ontdoor weathering trials, they exhibited considerable variation in moistnre content and developed severe surface checks, whereas the combined treatment showed snperior performance. 

Using an evaporator for raffinate concentration and production of strip solutions, a closed wet cycle is obtained and no aqueous waste pollutes the environment. 

When the wind velocity is lower, drying process could be larger and could be a significant part of the dry/wetness cycle. It also depends on the temperature existing on the metallic surface. On ISO-9223 there are not considered changes in the dry/wet cycles. 

---