Vapor dispersion enhancements

If aerosolization is a major contributor to a hazard, a portion of the airborne liquid can be removed by placing an angled plate over the release point. The released material strikes the plate, which disperses much of the momentum and enhances coagulation of liquid droplets. In this way a portion of the liquid will drop out of the cloud. However, the loss of momentum may result in less efficient vapor dispersion and, hence, a larger hazard area. 

Attempts can be made to minimize the impact area of hazardous vapor releases. This can be accomplished by taking steps to enhance near-field vapor dispersion and thus increase the dilution rate to break down aerosols, or to move the cloud away from sensitive areas. The techniques listed below have all been used ... 

The froth on the tray is a turbulent mass of usually liquid-continuous fluid with vapor dispersed in the form of small bubbles. The various designs of tray vapor openings attempt to maximize vapor dispersion by generating the smallest possible bubbles. The froth is where mass transfer takes place between the vapor and the liquid. Mass transfer and tray efficiency are enhanced by creating the largest possible interfacial area. 

When a liquid is dispersed into droplets the surface area is increased, which enhances the rates of heat and mass transfer. For a particular liquid dispersed at constant concentration in air the MIE varies with approximately the cube of surface average droplet diameter, hence the MIE decreases by a factor of about 8 when the surface average diameter D is halved (A-5-1.4.4). Ease of ignition is greatly enhanced for finely divided mists with D less than about 20 /rm, whose MIE approaches that of the vapor. Below 10 /rm a high flash point liquid mist (tetrahydronaphthalene) was found to behave like vapor while above about 40/rm the droplets tended to burn individually [ 142]. Since liquid mists must partially evaporate and mix with air before they ignite, the ease with which a liquid evaporates also affects MIE (Eigure 5-1.4.4). 

Water spray systems have been demonstrated to assist in the dispersion of vapor releases. The sprays assist in the dilution of the vapors with the induced air currents created by the velocity of the projected water particles. They cannot guarantee that a gas will reach an ignition source but do improve that probabilities that dispersion mechanisms will be enhanced. 

Coal is microporous, with certain partial molecular sieve properties. (A microporous solid herein refers to that which contains pores with diameters of a few tens of A. or less.) Micropores can be considered as entities capable of sorbing foreign molecules, and it is known that additivity of their sorption potential fields enhances the sorption owing to dispersion interactions. As the pores become progressively narrower, the vapor adsorption isotherm (Figure 1) in the initial region up to point B becomes progressively steeper (toward the... 

Some toxic chemicals have a strong affinity for water or other liquids. Sprays in the path of the cloud will absorb some of the chemical and will induce more turbulence in the cloud which can lead to enhanced dispersion. Water is used for vapors that have an affinity for water, for example halogen acids, and ammonia. 

H. van Bekkum et al. (17) reported that the alpha-pinene oxide 9 can be succesfully converted to campholenic aldehyde 10 (Eq. 15.2.5) in the presence of a BEA-zeolite. Ti-BEA proves to be an excellent catalyst for the rearrangement of a-pinene oxide to campholenic aldehyde in both the liquid and vapor phase. This is mainly attributed to the presence of isolated, well-dispersed titanium sites in a Bronsted-acid-free silica matrix. Furthermore, the unique molecularsized pore structure of the zeolite may enhance selectivity by shape-selectivity. 

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