Rapid flash vaporization

Point defect and super activity of metals. The catalytic activity of metal wire catalyst at high temperatures is markedly different before and after the occurrence of rapid flash vaporization. Before the rapid flash vaporization, the catalysts have normal activities. After the rapid flash vaporization at high temperatures, the activities of the metal wire catalysts such as Cu, Ni etc. increase approximately by 10 times, which are called as super activities. This is because of the formation of highly nonequilibrium concentrations of point defects after the high temperature flash vaporization, which is much important to produce the super activity of catalysts. It disappeares rapidly when it is treated with cooling due to the diffusion of vacancies and rapid displacement of surface atoms in it. 

The formation of droplets and their rapid, efficient vaporization is the reason that there is more vapor in the cloud than the amount which flashed off originally. Schmidli et al. (1990) determined that 5 to 50% of the mass of the original fuel can be found in droplets. This value depends upon initial mass and degree of superheat, that is, amount by which the fuel s temperature exceeds its boiling point. 

For packed columns, 0.1-10 pi of a liquid sample or solution may be injected into a heated zone or flash vaporizer positioned just ahead of the column and constantly swept through with carrier gas (Figure 4.18(a)). The zone is heated some 20-50°C above the column temperature to ensure rapid volatilization of the sample. Alternatively, to minimize the risk of decomposing thermally sensitive compounds and to improve precision, samples can be deposited directly onto the top of the packed bed of the column (on-column injection). 

This title is somewhat misleading. The following article is primarily concerned with expl reactions of fuel mists (and/or vapors) with oxygen of the air. The article does not include consideration of flash vaporizations that occur when very hot substances (molten A1 for example) come into contact with a volatile liquid (eg, water), nor does it concern itself with steam-boiler type explns. Thus the subject matter of this article deals with rapid fuel oxidations with the oxidant usually provided by the oxygen of the air, though reactions of monopropellant type mists will also be considered. Most of the fuels of interest are liquids at ordinary ambient conditions... 

Flammable Any chemical substance, liquid or solid, that has a flash point of 100°F or below any solid that can sustain fire and ignite readily any material that can be ignited easily and will burn rapidly Flash point The temperature at which a liquid will generate sufficient vapors to promote combustion. Generally, the lower the flash point is, the greater the danger of combustion is... 

Many rDA reactions are carried out at temperatures of 150 C or more in solution phase and often at temperatures of 400-600 C using the flash vapor pyrolysis (FVP) method individual conditions are referenced throughout the text. However, an accelerating effect by anionic, cationic and radical substimtion on either the dienophile or at the termini of the diene fragments has been predicted by Carpenter.Experimentally, this prediction has been substantiated only for anionic substitution. In 1967, Hart reported what is likely the first example of an oxyanion-accelerated rDA reaction. Both oxyanionic " and car-banionic substituents accelerate the cycloreversion reaction such that they proceed rapidly at room temperature (for example, equation 3). In addition, acid-catalyzed rDA reactions have been reported in which protonation effectively makes the dienophile fragment of the adduct more electron deficient. Grieco has utilized a room temperature retro aza DA reactitm useful for the N-methylation of dipeptides and amino acid derivatives (equatitm 4). ... 

Shortcut calculation methods. In the remainder of this chapter, shortcut calculation methods for the approximate solution of multicomponent distillation are considered. These methods are quite useful to study a large number of cases rapidly to help orient the designer, to determine approximate optimum conditions, or to provide information for a cost estimate. Before discussing these methods, equilibrium relationships and calculation methods of bubble point, dew point, and flash vaporization for multicomponent systems are covered. 

Packed Flash-vaporization Sample injected into zone heated to 20-50°C above column temperature Rapid volatilization of sample, but thermal degradation of some solutes may occur... 

Diketene is a flammable Hquid with a flash point of 33°C and an autoignition temperature of 275°C. It decomposes rapidly above 98°C with slow decomposition occurring even at RT. The vapors are denser than air (relative density 2.9, air air = 1). The explosive limits in air are 2—11.7 vol % (135). In case of fire, water mist, light and stabilized foam, as well as powder of the potassium or ammonium sulfate-type should be used. Do not use basic extinguisher powders and do not add water to a closed container. 

A vapor poeket on the exchanger s low-pressure side can create a cushion that may greatly diminish the pressure transient s intensity. A transient analysis may not be required if sufficient low-pressure side vapor exists (although tube rupture should still be considered as a viable relief scenario). However, if the low-pressure fluid is liquid from a separator that has a small amount of vapor from flashing across a level control valve, the vapor pocket may collapse after the pressure has exceeded the fluid s bubble point. The bubble point will be at the separator pressure. Transient analysis will prediet a gradually inereasing pressure until the pressure reaches the bubble point. Then, the pressure will increase rapidly. For this ease, a transient analysis should be considered. 

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