Burning surface

Foams are used industrially and are important in rubber preparations (foamed-latex) and in fire fighting. The foam floats as a continuous layer across the burning surface, so preventing the evolution of inflammable vapours. Foams are also used in gas absorption and in the separation of proteins from biological fluids. See anti-foaming agents. 

If an ethyl ether fire occurs, carbon dioxide, carbon tetrachloride, and dry chemical fire extinguishers meeting National Eire Prevention Association Code 1 and 2 requirements may be used successhiUy (23). Water may also be effectively appHed (see Plant safety). Hose streams played into open tanks of burning ethyl ether serve only to scatter the Hquid and spread the fire. However, ether fires may be extinguished by a high pressure water spray that cools the burning surface and smothers the fire. Automatic sprinklers and deluge systems are also effective. 

Calcium carbonate - emits non-flammable gases and helps to reduce the supply of oxygen lo the burning surfaces. The FRLS cables thus produced would possess the required properties... 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

Korotkov et al (Ref 67) also stress the importance of convective burning in DDT. They claim that the length of the run-up zone to detonation is determined by dp/dt in the burning zone. The value of dp/dt in turn is determined by the specific burning surface and the permeability, pore size and compressibility of the expl... 

As = burning surface area (sq inches), p = proplnt density (lb/cu inch). For stable operation, the mass flow rate must equal the mass discharge rate at the nozzle which is... 

For some purposes, it is indeed desirable that the rate of burning should increase during the process rather than remain constant. This is true in certain guns. For such purposes grains can be produced perforated by a number of holes so that the burning surface increases as combustion proceeds. For rockets special constructions are used which are discussed in Chapter 19. 

Web thickness. The distance of travel of a burning surface in a propellent grain to give complete combustion. 

Thermal burns result from the radiant heat emitted by a hydrogen fire and absorbed by a person, which is directly proportional to many factors including exposure time, burning rate, heat of combustion, size of the burning surface, and atmospheric conditions (mainly wind and humidity). For instance, thermal radiation flux exposure level of 0.95 W/cm2 may cause skin burns in 30 s. Cryogenic burns may result from contact with cold fluids or cold vessel surfaces. Exposure to large liquefied hydrogen spills could result in hypothermia, if proper precautions are not taken [17]. 

Foam breaks down and vaporizes its water content when exposed to heat and flame. Therefore, it must be applied to a burning surface at a sufficient rate to compensate for this loss and to ensure a residual foam layer over the liquid. 

Heat and mass transfer through the boundary layer flow over the burning surface of propellants dominates the burning process for effechve rocket motor operation. Shock wave formahon at the inlet flow of ducted rockets is an important process for achieving high propulsion performance. Thus, a brief overview of the fundamentals of aerodynamics and heat transfer is provided in Appendices B -D as a prerequisite for the study of pyrodynamics. 

---