Surface condensers problems with

In Chap. 23 we reviewed several problems pertaining to steam jet precondenser and intercondenser problems. The surface condensers, which serve condensing steam turbines, are subject to all the same problems and a lot more. A standard surface condenser package with an associated two-stage jet system is shown in Fig. 25.3. By way of summarizing many of the problems that occur with this sort of equipment, I will relate my trials and tribulations with K-805, an auxiliary combustion air blower at the Good Hope Refinery in Norco, Louisiana (now Valero). 

Condensate from contact units cannot be reused and may constitute a waste disposal problem. Surface condensers can be used to recover valuable condensate. Surface condensers must be equipped with more auxiliary equipment and generally require a greater degree of maintenance. 

Barometric condenser systems can be a major source of contamination in plant effluents and can cause a particularly difficult problem by producing a high-volume, dilute waste stream [8]. Water reduction can be achieved by replacing barometric condensers with surface condensers. Vacuum pumps can replace steam jet eductors. Reboilers can be used instead of live steam reactor and floor washwater, surface runoff, scrubber effluents, and vacuum seal water can be reused. 

It may be convenient to consider the entire system to be confined within a very large container having inpenetrable walls if realistic equilibrium of vapour and condensed phases is important. In cases of immediate interest, the true vapour phase is not an essential feature and the relatively small volume occupied by the condensed phase is the more important thermodynamical variable. There are still subtleties associated with taking the thermodynamic limit, particularly when isolating surface and bulk effects, but the problems with vanishing density of particles can be controlled. 

Other methods of surface area determination depend, in general, on adsorption under well defined conditions of various solute molecules of known dimensions (Sposito, 1984 Davis and Kent, 1990). Some of these are dipole molecules so that dipole interactions with the surface or H-bonding are involved. Water adsorbed at a fixed relative water vapour pressure (e. g. 0.2) to provide a monolayer is one example (Torrent et ah, 1990). An organic dipole frequently used for soils is ethylene glycol monoethylether (EGME) (Carter et al., 1965). The main problem with these dipole molecules lies in their mutual association which may lead to localized adsorption beyond a monolayer (capillary condensation), particularly on porous material. 

Recently, the Horvath-Kawazoe (HK) method for slit-like pores [40] and its later modifications for cylindrical pores, such as the Saito-Foley (SF) method [41] have been applied in calculations of the mesopore size distributions. These methods are based on the condensation approximation (CA), that is on the assumption that as pressure is increased, the pores of a given size are completely empty until the condensation pressure corresponding to their size is reached and they become completely filled with the adsorbate. This is a poor approximation even in the micropore range [42], and is even worse for mesoporous solids, since it attributes adsorption on the pore surface to the presence of non-existent pores smaller than those actually present (see Fig. 2a) [43]. It is easy to verify that the area under the HK PSD peak corresponding to actually existing pores does not provide their correct volume, so the HK-based PSD is not only excessively broad, but also provides underestimated volume of the actual pores. This is a fundamental problem with the HK-based methods. An additional problem is that the HK method for slit-like pores provides better estimates of the pore size of MCM-41 with cylindrical pores than the SF method for cylindrical pores. This shows the lack of consistency [32,43]. Since the HK-based methods use CA, one can replace the HK or SF relations between the pore size and pore filling pressure by the properly calibrated ones, which would lead to dramatic improvement of accuracy of the pore size determination [43] (see Fig. 2a). However, this will not eliminate the problem of artificial tailing of PSDs, since the latter results from the very nature of HK-based methods. 

Most unfortunately, an incorrect correlation for heat-transfer coefficients for surface condensers has become widely disseminated in several books devoted to heat transfer. This correlation predicts heat-transfer coefficients, for clean condensers, of about 650, when the water-side velocity is about 6 ft/s. Use of this correlation has led to some extremely serious problems, with which your author is intimately acquainted. 

The temperature for Bose-Einstein condensation varies with density as n20. Because density is limited by three-body recombination, the search for the transition leads naturally to lower temperatures. Unfortunately, at temperatures below 0.1 K, adsorption rapidly becomes prohibitive. To avoid this problem, Hess [4] suggested confinirig the atoms in a magnetic trap without any surfaces. The states confined are the "low-field seeking" states, (HT, electron spin "up"). These are the hyperfine states (F-l,m-l) and (F=l,m=0). 

In cases where the particle surfaces are not wettable, condensation proceeds with much more difficulty. This is because the condensing liquid tends to pull into small spheres on the particle surface, and only when the entire surface is covered with these spheres is a liquid coating formed. Fletcher (1958a, b) has treated this problem by considering the contact angle between an embryo sphere formed on the particle and the particle surface. His results correspond to what has been observed experimentally—it is very difficult to get condensation to take place on nonwettable particles unless high supersaturations are used. The role of insoluble nuclei in the condensation process is still in question and remains another problem for future investigators to solve. 

Abstract. Propagation of capillary waves along the surface of water covered by a homogeneous insoluble film has been a subject of numerous experimental and theoretical studies. However, it has been shown only recently that real surface films contain two-dimensional aggregates, which influence the characteristics of surface waves. The problem of multiple scattering of surface waves by two dimensional viscoelastic particles is considered briefly below. The results can be compared with the experimental data for condensed films with two-dimensional bubbles of gaseous phase. 

This is in fact the high-pressure limit and a reasonable maximum for po, since at higher po there would be condensation of O2 on the surface. Some studies therefore assume a slightly lower po [77]. Problems with the FP calculation of (02) are discussed below. Notwi standing these, this po is for example appropriate for estimating ysurf of the oxygen-healed (1x1) rutile surface (section 5). 

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