Thin sprays

Due to computer storage and run time limitations, it is not yet possible to accurately model the details of flows around each individual droplet in a spray. Thus, empirical or semi-empirical correlations are typically used to model the exchange processes between droplets and gas. Correlations for drag coefficients have been suggested by many researchers.[45l[559h568Fl571l For thin sprays, the drag... 

Most current multidimensional spray simulations have adopted the thin or very thin spray assumptions,[55°1 i.e., the volume occupied by the dispersed phase is assumed to be small. This can be justified if a simulation starts some distance downstream of the nozzle exit, where the gas volume fraction is large enough, or if the computational cells are relatively large. Accordingly, two major classes of models have been used in spray modeling locally homogeneous flow (LHF) models and two-phase-flow or separated-flow (SF) models. 

Batchelor GS, Walker KC, Elliott JW. 1956. Dinitroorthocresol exposure from apple-thinning sprays. AMA Arch Indus Health 13 593-596. 

Figure 9 Disk-Coater fat coating system. Product is metered into a steam-coii heated chamber through a rotary iock feeder and is thrown off the upper rotating disk by centrifugai force. The particies faii through a thin spray of fat simuitaneousiy thrown off the tower rotating disk. Mixing and absorption are continued in the takeaway conveyor. Courtesy of ASIMA Corp., independence, Kansas.

Filter the precipitate in Buchner funnel under suction and wash with a thin spray of cold water. 

Mist coat n. (1) Very thin sprayed coat. (2) A thin coat of volatile thinners, with or without a small amount of lacquer, which is sprayed over a dry lacquer film to improve the smoothness and luster. 

Figure 10. Crack deflection mechanisms in TBC. a) Segmentation crack deflects on intact spraying splat, b) Delamination crack bounces between surfaces of thin spray splat. Crack propagation from top to bottom.

Red copper oxide may be used as an underglaze, being best produced by very thin sprays of copper oxide underneath a soft soda glaze. 

For supercapacitors made with SWCNT, a specific capacitance of around 80 F/g was observed in liquid aqueous electrolytes. For supercapacitors made with thin sprayed films using the same SWCNT material, the specific capacitance was around 120 F/g. This indicated that wetting was better in thin CNT films, increasing the effective surface area. This was valid even in the case of a gel electrolyte. The capacitance was found to increase linearly for the liquid electrolyte, whereas saturation occurred for the gel electrolyte, which indicated a limited penetration into the gel network. From the study it was concluded that the optimum thickness of the CNT film should be around 2 jm for the gel electrolyte. The RC constants for the supercapacitor were around 0.5 s for aqueous electrolytes and 0.1 and 0.3 s for the organic electrolyte at 1 and 3 V respectively. The power density obtained in the organic electrolyte was about 70 kW/kg. The concept of printed power without a current collector offers a new platform for all kinds of lightweight devices. 

Bonded Solid-Film Lubricants. Although a thin film of soHd lubricant that is burnished onto a wearing surface often is useful for break-in operations, over 95% are resin bonded for improved life and performance (62). Use of adhesive binders permits apphcations of coatings 5—20 p.m thick by spraying, dipping, or bmshing as dispersions in a volatile solvent. Some commonly used bonded lubricant films are Hsted in Table 12 (62) with a more extensive listing in Reference 61. 

Finish removers are appHed by bmshing, spraying, troweling, flowing, or soaking. Removal is by water rinse, wipe and let dry, or solvent rinse. Removers may be neutral, basic, or acidic. The viscosity can vary from water thin, to a thick spray-on, to a paste trowel-on remover. The hazard classification, such as flammable or corrosive, is assigned by the U.S. Department of Transportation (DOT) for the hazardous materials contained in the remover. 

Water Dispersions. Polysulftde products are offered as aqueous dispersions (Thiokol WD-6). These are useful for applyiag protective coatings to line fuel tanks, and for concrete, wood, and ia some cases fabrics, felt, leather (qv), and paper (qv). It has been found that a stable emulsion can be made that contains both LP and manganese oxide curing agent. The emulsion can be thinned and appHed as a spray coating. After it is appHed, water evaporates and the LP cures to form a soHd mbber (13). 

Although the continuous casting of steel appears deceptively simple in principle, many difficulties are inherent to the process. When molten steel comes into contact with a water-cooled mold, a thin soHd skin forms on the wall (Eig. 10). However, because of the physical characteristics of steel, and because thermal contraction causes the skin to separate from the mold wall shortly after solidification, the rate of heat abstraction from the casting is low enough that molten steel persists within the interior of the section for some distance below the bottom of the mold. The thickness of the skin increases because the action of the water sprays as the casting moves downward and, eventually, the whole section solidifies. 

Several plants employ cooled-belt flakers. These consist of flexible steel belts, ca 1-m wide and up to 50-m long, that have short mbber skirting at the edges. Molten pitch flows from a thermostatically controlled tank over a weir to give a flat thin sheet on the belt, which is cooled from below by water sprays. At the end of the belt, the solid pitch is broken up by rotating tines. The pitch flakes are drained and transported to a covered storage silo by belt conveyor, during which time the surface moisture evaporates. 

Spray Pyrolysis. In spray pyrolysis, a chemical solution is sprayed on a hot surface where it is pyrolyzed (decomposed) to give thin films of either elements or, more commonly, compounds (22). Eor example, to deposit CdS, a solution of CdCl plus NH2CSNH2 (thiourea) is sprayed on a hot surface. To deposit Iu202, InCl is dissolved in a solvent and sprayed on a hot surface in air. Materials that can be deposited by spray pyrolysis include electrically conductive tin—oxide and indium/tin oxide (ITO), CdS, Cu—InSe2, and CdSe. Spray pyrolysis is an inexpensive deposition process and can be used on large-area substrates. 

Poly(vinyl acetate) latex paints are the first choice for interior use (149). Their abihty to protect and decorate is reinforced by several advantages belonging exclusively to latex paints they do not contain solvents so that physiological harm and fire ha2ards are eliminated they are odorless they are easy to apply with spray gun, roUer-coater, or bmsh and they dry rapidly. The paint can be thinned with water, and bmshes or coaters can be cleaned with soap and tepid water. The paint is usually dry in 20 minutes to two hours, and two coats may be applied the same day. 

Surface Applied Surfactants. Antistat agents can be appHed direcdy to the surface of a plastic part. Usually the antistat is diluted in water or in a solvent. The antistat solution is appHed by spraying, dipping, or wiping on the surface. The water or solvent dries leaving a thin film that attracts moisture. Since it is appHed to the surface, migration through the resin is not a factor. In practice, the quaternary ammonium compounds find the most use. They are soluble in water and effective at low concentrations. 

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