Flash vaporized sprays

Keywords Fire suppression Flame extinguishment Flame suppression screens Flash vaporized sprays Spray transport Sprinklers Water mists... 

A liquefied gas is widely sprayed from the exit developing a multi-phase mixture. In the opening, a narrow, so-called flashing zone is formed in which a certain firaction of the liquid depending on its thermodynamic conditions is spontaneously (flash-) vaporized. Adjacent zones are the zone of flow establishment characterized by a dilution of the jet stream from its boundaries and the zone of established flow with the full development of the plume interacting with the ambient [84]. 

Equation (10.38) provides the vapour quality under equilibrium conditions. In practical emission simations part of the liquid is discharged as spray. The droplets then formed receive their enthalpy of vaporization from the surrounding air. In this way the fraction of vaporized liquid is substantially increased. Often one assumes that the fraction of liquid spray is equal to that vaporized by flash vaporization. If the fraction vaporized by flashing is small, about 5 %, one may assume that the quantity vaporized due to spray formation is two or three times that vaporized by flashing. 

The slot in the interfaces for passage of the belt is formed by two "L"-shaped sapphire pieces which are attached to the stainless-steel flange or vacuum closure bar by epoxy cement. The belts used are either 0.05 or 0.075 mm thick and the slot tolerance is set to be 0.075 mm greater than the belt thickness (i.e., either 0.125 or 0.15 mm). The belt width is 0.317 cm and the slot width is 0.325 cm. A ribbon 0.32 cm wide travelling at a speed of 2.5 cm/sec will carry away a liquid film 0.2 mm thick from a solvent flow of 1 ml/min and if the solvent film can be evaporated without loss of solute, then the ribbon will transport virtually 100% of the solute into the mass spectrometer. Sample utilization will then depend only on the efficiency of the flash vaporization step. In practice, some sample is lost by spray processes and the flash vaporization cannot be fully efficient for all compounds. Nevertheless, yields in the range of 25-40% have been attained with an LC/MS ribbon interface system. It follows that the quantity of column eluent taken from the ribbon will be twenty times greater than that taken by the wire and provide significantly improved sensitivity. 

Absorber is a component where strong absorber solution is used to absorb the water vapor flashed in the evaporator. A solution pump sprays the lithium bromide over the absorber tube section. Cool water is passing through the tubes taking refrigeration load, heat of dilution, heat to cool condensed water, and sensible heat for solution coohng. 

A major portion of the reaction is found to occur in the vapor space between trays. A unit in which most of the trays are replaced oy empty space is called a. flash roaster its mode of operation is like that of a spray dryer. 

Fire Hazards - Flash Point (deg. F) 20 CC Flammable Limits in Air (%) 2.8 - 14.4 Fire Extinguishing Agents Stop flow of gas. Use water spray, carbon dioxide, or dry chemical for fires in water solutions Fire Extinguishing Agents Not to be Used Do not use foam Special Hazards of Combustion Products Vapors are eye, skin and respiratory irritants Behavior in Fire Not pertinent Ignition Temperature (deg. F) 756 Electrical Hazard Data not available Burning Rate 4.5 mm/min. 

The property of LFG that makes it so hazardous is that it is usually stored and handled under pressure at temperatures above normal boiling points. Any leak thus flashes, much of it turning to vapor and spray. This can spread for hundreds of meters before it reaches a source of ignition. 

A visible cloud of vapor, 1 m deep, spread for 150 m and was ignited by a car that had stopped on a nearby road 25 minutes after the leak started. The road had been closed by the police, but the driver approached from a side road. The fire flashed back to the sphere, which was surrounded by flames. There was no explosion. The sphere was fitted with water sprays. But the system was designed to deliver only haif the quantity of water normally reeommended (0.2 U.S. gal/ft- min. or 8 L/m min.), and the supply was inadequate. When the fire brigade started to use its hoses, the supply to the spheres ran dry. The firemen seemed to have used most of the available w ater for cooling neighboring spheres to stop the fire from spreading, in the belief that the relief valve would pro-teet the vessel on fire. 

To allow for spray- and aerosol-formation, the mass of fuel in the cloud is assumed to be twice the theoretical flash of the amount of material released, so long as this quantity does not exceed the total amount of fuel available. Blast effects are modeled by means of TNT blast data according to Marshall (1976), while 1 bar is considered to be upper limit for the in-cloud overpressure (Figure 4.18). Because experience indicates that vapor clouds which are most likely to explode... 

Spray and mists releases generally behave like a gas or vapor release. The fuel is highly atomized and mixed with air. Sprays or mists can easily be ignited, even below the flash point temperature of the material involved, since mixing of the fuel with the air has already occurred. 

Most combustible liquids do not present a vapor problem if accidentally released into the atmosphere. The probability of a fire, therefore, is considerably less than it would be if the spill was of a flammable material. If, however, the combustible liquid is at a temperature higher than its flashpoint, then it can be expected to behave in the identical manner a flammable liquid. One major difference between the two in a fire situation is that the potential exists for cooling the combustible liquid below its flash point by the proper application of water (generally applied in the form of water spray). In the event the liquid is burning, and if the fire forces are successful in achieving the required reduction in liquid temperature, then vapor production will cease and the fire will be extinguished because of a lack of vapor fuel. Unless this reduction in liquid temperature can be brought about, the fire will necessitate the same control considerations a low-flash liquid fire would. 

Vapor forms explosive mixtures with air. Flammable limits, 3-17%. Flash point, 0°C. Ignition temperature, 481°C. Dilute solutions are also hazardous. Extinguish fires with water spray, dry chemical, foam, or carbon dioxide.2... 

Flash point, 27°C. Extinguish fire with water spray, dry chemical, carbon dioxide, or vaporizing liquids.2... 

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