Flash volatilization, rapid vaporization

The separation of a volatile component from a liquid process stream can be achieved by way offlash distillation. It is referred to as a flash since the more volatile component of a gas mixture rapidly vaporizes upon entering a tank or drum that is at a lower pressure and/or a higher temperature than the incoming feed. If the feed is considered to be cold, a pump and heater may be required to elevate the pressure and temperature, respectively, to achieve an effective flash (see Figure 26). As the feed enters the tank/drum, it may impinge against the wall or an internal deflector plate, which would promote liquid-vapor separation of the feed mixture. 

Materials that dissociate in the vapor phase may provide solid films with a stoichiometry that differs from that of the source. Therefore, special techniques have been devised. One approach is to use the method of flash evaporation. Rapid evaporation is achieved by continuously dropping fine particles of the materials onto a hot surface. Although fractionation occurs during the evaporation of each particle (the more volatile component evaporating first), at any time there will be several particles at different stages of fractionation. Consequently, the vapor phase will possess a similar... 

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... 

FLASH POINT. The lowest temperature at which an oil will volatilize to yield sufficient vapor to form with air an inflammable gaseous mixture, demonstrable through the production of a flush on comacl w ith a small open Hume. The flash point occurs at a temperature lower than the burning point, w hich is the lowest temperature at which the production of combustible gas occurs rapidly enough in support a steady flame. It is also m be noted that the flash point is the temperature of formation, under the test conditions, of the losver explosive mixture of the substance tested, with air. iThc higher explosive mixture is the maximum concentration of vapor, with air. which will sustain combustion.)... 

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... 

---