Enhanced Condensing Surfaces

Instances have been found in which BET plots were noted to be linear to relative pressures as high as 0.5, and in other cases the linear range is found only below relative pressures of 0.1.The extent to which these deviations from the usual range of linearity reflect unusual surface properties is difficult to ascertain. For example, micropores exhibit unusually high adsorption potentials due to the overlapping potential from the walls of the micropore. Under these enhanced conditions condensation can occur within the pores at relative pressures less than 0.1, and linear BET plots are found at even lower relative pressures. 

Non-aqueous synthetic methods have recently been used to assemble mesoporous transition metal oxides and sulfides. This approach may afford greater control over the condensation-polymerization chemistry of precursor species and lead to enhanced surface area materials and well ordered structures [38, 39], For the first time, a rational synthesis of mesostructured metal germanium sulfides from the co-assembly of adamantanoid [Ge4S ()]4 cluster precursors was reported [38], Formamide was used as a solvent to co-assemble surfactant and adamantanoid clusters, while M2+/1+ transition metal ions were used to link the clusters (see Fig. 2.2). This produced exceptionally well-ordered mesostructured metal germanium sulfide materials, which could find application in detoxification of heavy metals, sensing of sulfurous vapors and the formation of semiconductor quantum anti-dot devices. 

As the size of species increases due to reactions in gas phase, the vapor pressure of the species decreases, enhancing the condensation (deposition of reactive species) on the surface. 

Enhanced surfaces can often significandy increase the effective heat-transfer coefficient in condensation, especially if the condensing heat-transfer coefficient is the limiting factor in the overall heat-transfer-coefficient equation. Such enhancements include low fins on horizontal tubes, which increase the heat-transfer area, and fluting on vertical tubes and plane surfaces, which thins the condensate film over part of the surface by surface-tension effects. However, these improvements are limited by condensate retention between the fins and flooding of the drainage paths [7, 34],... 

These results for a refrigerant, and the data of Marto et al. [154] and Mehta and Rao [156] for steam, provide good practical guidance for the use of enhanced tubes in surface condensers. 

In order to stimulate condensate motion under zero-G conditions, other forces must replace the gravitational force. This may be done by centrifugal forces, vapor shear forces, surface tension forces, suction forces, and forces created by an electric field. McEver and Hwangbo [133] and Valenzuela et al. [134] describe how surface tension forces may be used to drain a condenser surface in space. Tanasawa [1] reviews electrohydrodynamics (EHD) enhancement of condensation. Bologa et al. [135] showed experimentally that an electric field deforms the liquid-vapor interface, creating local capillary forces that enhance the heat transfer. 

L. L. Vasiliev and V. V. Khrolenok, Heat Transfer Enhancement with Condensation by Surface Rotation, Heat Recovery Sys. and CHP, 13, pp. 547-563,1993. 

Ceramic powders and films made by gas-phase techniques and their characterization are discussed by C. L. J. Adkins and D. E. Peebles. Ultrafine ceramic particles with enhanced surface reactivity, such as Si02, can be synthesized through nucleation or condensation reactions in gas-phase aerosols. Ceramic films and... 

Enzymatic techniques can be used to endow proteins with surface-active functionality. An enzymatic technique that has shown promise in enhancing surface properties of proteins is a modified version of the classical plastein reaction. The plastein reaction is known to be a protease-catalyzed reverse process in which a peptide-peptide condensation reaction [11,12] proceeds through the peptidyl-enzyme intermediate formation [13]. It is essentially a two-step process enzymatic hydrolysis of a protein and plastein formation from the hydrolysate peptides. A novel one-step process was developed as a modified type of the plastein reaction by Yamashita et al. [14,15], which... 

There is a suggestion that peak heat fluxes in the evaporators of rotating heat pipes increase as the one-fourth power of acceleration (Costello and Adams, 1960). While the condenser performance has been less well documented, high G forces allow very thin film thicknesses and continuous irrigation of the surface, reducing the thermal resistance across it. Because of the sealed nature of heat pipes and other rotating devices, even further enhancement of condenser performance could be achieved by promoting drop-wise condensation. 

From the above results, it could be concluded that the addition of excess amount of sodium ions into the crystallization system has apparent effect on the particulate properties of the product. At low batch alkalinity, the additional sodium ions causes de-aggregation of the final products, rendering the particles with more uniform size distributions. At high batch alkalinity, the excess amount of sodium ions triggers the surface condensation reactions on the crystalline end products. However, the crystallization rate is not enhanced by the increase of batch sodium ion content, indicating that the determining factor of crystallization of ZSM-5 zeolites in SDA-free system is concentration of low molecular weight silicate species, determined by batch alkalinity. 

Because this type of operation essentially involves the Nusselt theory with enhanced liquid flow, a heat transfer coefficient approach is used for calculative purposes, rather than transfer units. Temperature differences are calculated as if a surface condenser were being used. If a single-component vapor is condensing at a constant pressure, the temperature difference at the liquid coolant inlet is T — q. Similarly, the temperature difference at the liquid coolant outlet is Ti — to- This is true because the vapor temperature remains constant from the first drop of condensate to the last drop. Thus, the logarithmic mean temperature driving force is ... 

As mentioned in Section IX-2A, binary systems are more complicated since the composition of the nuclei differ from that of the bulk. In the case of sulfuric acid and water vapor mixtures only some 10 ° molecules of sulfuric acid are needed for water oplet nucleation that may occur at less than 100% relative humidity [38]. A rather different effect is that of passivation of water nuclei by long-chain alcohols [66] (which would inhibit condensation note Section IV-6). A recent theoretical treatment by Bar-Ziv and Safran [67] of the effect of surface active monolayers, such as alcohols, on surface nucleation of ice shows the link between the inhibition of subcooling (enhanced nucleation) and the strength of the interaction between the monolayer and water. 

The pores in question can represent only a small fraction of the pore system since the amount of enhanced adsorption is invariably small. Plausible models are solids composed of packed spheres, or of plate-like particles. In the former model, pendulate rings of liquid remain around points of contact of the spheres after evaporation of the majority of the condensate if the spheres are small enough this liquid will lie wholly within the range of the surface forces of the solid. In wedge-shaped pores, which are associated with plate-like particles, the residual liquid held in the apex of the wedge will also be under the influence of surface forces. 

Dicylopentadiene Resins. Dicyclopentadiene (DCPD) can be used as a reactive component in polyester resins in two distinct reactions with maleic anhydride (7). The addition reaction of maleic anhydride in the presence of an equivalent of water produces a dicyclopentadiene acid maleate that can condense with ethylene or diethylene glycol to form low molecular weight, highly reactive resins. These resins, introduced commercially in 1980, have largely displaced OfXv o-phthahc resins in marine apphcations because of beneficial shrinkage properties that reduce surface profile. The inherent low viscosity of these polymers also allows for the use of high levels of fillers, such as alumina tfihydrate, to extend the resin-enhancing, fiame-retardant properties for apphcation in bathtub products (Table 4). 

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