Flame speed ideal

Blast effects can be represented by a number of blast models. Generally, blast effects from vapor cloud explosions are directional. Such effects, however, cannot be modeled without conducting detailed numerical simulations of phenomena. If simplifying assumptions are made, that is, the idealized, symmetrical representation of blast effects, the computational burden is eased. An idealized gas-explosion blast model was generated by computation results are represented in Figure 4.24. Steady flame-speed gas explosions were numerically simulated with the BLAST-code (Van den Berg 1980), and their blast effects were calculated. 

In Chapter 4 we examined the spread rate of a premixed flame and found that its speed, Su, depended on the rate of chemical energy release, m Ahc. Indeed, for a laminar flame, the idealized flame speed... 

This initial condition is rather idealized. In reality, one would expect to see partially premixed zones with f = fst and 7 = 0 which will move towards 7 = 1 along the stoichiometric line. The movement along lines of constant f corresponds to premixed combustion, and occurs at a rate that is controlled by the interaction between molecular diffusion and chemical reactions (i.e., the laminar flame speed). 

Turbulence created during a release process does not have a long lifetime. However, if an ignition hits this narrow time window of ideal turbulence and concentration distribution, a high flame speed can be reached. 

The reaction rate, m ", and flame thickness, <5r, are related to the ideal burning speed by... 

Two other systems that produce high-temperature molecules should be mentioued shock waves and flames. Shock waves are typically formed by the rapid release of a high pressure of gas in a shock-tube apparatus. A shock wave is formed that can travel at several times the speed of sound temperatures as high as 20 000 K have been produced in shock tubes. Thus the method is ideal for monitoring pyrolysis and oxidation reactions. Flames are gaseous systems where a flow of gas combines with a self-supporting reaction to produce a steady-state situation. Again, oxidation reactions are amenable to this approach. In particular, short-hved intermediates in hydrocarbon oxidation, such as C2, OH, and CHO+, have been identified in flames. 

Ex. 1. Tuftane film is ideally suited for bonding emblems, numerals, and letters to many fabrics by heat and pressure alone. It also flame-bonds well to both polyester- and polyether-urethane foams at commercial bonding speeds. Since it contains no volatiles it does not require cure times as do solvent- or water-based adhesive systems. All Tuftane films can be adhered thermally by hot bar, thermal impulse, ultrasonic, or dielectric methods over a wide range of temperatures. Adhesive lamination to many substrates is possible by the heated drum, curing oven, or multiple can methods. Fabric bonds made with Tuftane are strong and withstand laundering and dry cleaning. 

In region HI, bounded by the lines corresponding to Kax = 1 at the bottom and Dax = 1 at the top, the reaction zone thickness grows and the flame cannot be described by the flamelet approach based on the laminar curved flame model. As a limiting case the ideal mixing reactor model (the chemical reaction speed is neglected in comparison with the turbulent mixing time) is considered. 

The effect of air/gas ratio on treatment level is shown in Figures 3 4 for natural and propane gases. This illustrates that a lean air/gas ratio provides the highest treatment level. At sub-stoichiometric air/fuel ratio, the treatment is not as high as the ideal ratio which while lean, depends on the substrate, and line speed. If the air/gas mixture is too lean, the treatment drops off. This shows how critical the air/gas ratio is in regard to optimizing flame surface treatment. 

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