Flames impingement

The end or front of the plasma flame impinges onto a metal plate (the cone or sampler or sampling cone), which has a small hole in its center (Figure 14.2). The region on the other side of the cone from the flame is under vacuum, so the ions and neutrals passing from the atmospheric-pressure hot flame into a vacuum space are accelerated to supersonic speeds and cooled as rapid expansion occurs. A supersonic jet of gas passes toward a second metal plate (the skimmer) containing a hole smaller than the one in the sampler, where ions pass into the mass analyzer. The sampler and skimmer form an interface between the plasma flame and the mass analyzer. A light... 

Flame spraying is no longer the most widely used melt-spraying process. In the power-feed method, powders of relatively uniform size (<44 fim (325 mesh)) are fed at a controlled rate into the flame. The torch, which can be held by hand, is aimed a few cm from the surface. The particles remain in the flame envelope until impingement. Particle velocity is typically 46 m/s, and the particles become at least partially molten. Upon impingement, the particles cool rapidly and soHdify to form a relatively porous, but coherent, polycrystalline layer. In the rod-feed system, the flame impinges on the tip of a rod made of the material to be sprayed. As the rod becomes molten, droplets of material leave the rod with the flame. The rod is fed into the flame at a rate commensurate with melt removal. The torch is held at a distance of ca 8 cm from the object to be coated particle velocities are ca 185 m/s. 

Red Brass Alloys. In forming red brass alloys, which iaclude leaded red and leaded semired brasses, caution should be exercised to prevent gas absorption by flame impingement or the melting of oily scrap, or metal loss through excessive oxidation of the melt surface. To prevent excessive 2iac volatilization, the melt must be poured as soon as it reaches the proper temperature. The melt should be finally deoxidized and cast at ca 1065—1230°C as measured with a pyrometer. Fluxing is usually not needed if clean material has been melted. 

Improper operation of a process may result in the vessel s exceeding design temperature. Proper control is the only solution to this problem. Maintenance procedures can also cause excessive temperatures. Sometimes the contents of a vessel may be burned out with torches. If the flame impinges on the vessel sheh, overheating and damage may occur. 

A common cause of a BLE T] in plants of the hydrocarbon-chemical industry is exposure to fire. With an external fire below the liquid level in a vessel, the heat of vaporization provides a heat sink, as with a teakettle evolved vapors exit tnrough the relief valve. But if the flame impinges on the vessel above the liquid level, the metal will weaken and may cause the vessel to rupture suddenly, even with the relief valve open. The explosive energy for a BLE T] comes from superheat. This energy is at a maximum at the superheat hmit temperature. (SLT is the maximum temperature to which a hquid can be heated before homogeneous nucleation occurs with explosive vaporization of the hquid and accompanying overpressure.) The SLT... 

Eliminate turned-down vents from safety relief valves, i.e., upside down U. Possible accidental ignition of releases from such vents wiU likely result in flame impingement on the top external surface of the tank, above the internal wetted surface. BLEXT Some means to handle rainwater from a desirable upward vertical vent have been listed by Bodurtha (ibid., April 1988). Moreover, a safety relief valve must function properly when required and must be sized properly to help prevent an explosion. 

Carhon Monoxide Carbon monoxide is a key intermediate in the oxidation of all hydrocarbons. In a well-adjusted combustion system, essentially all the CO is oxidized to CO9 and final emission of CO is veiy low indeed (a few parts per million). However, in systems which have low temperature zones (for example, where a flame impinges on a wall or a furnace load) or which are in poor adjustment (for example, an individual burner fuel-air ratio out of balance in a multiburner... 

The part that marries the plasma to the mass spectrometer in ICPMS is the interfacial region. This is where the 6000° C argon plasma couples to the mass spectrometer. The interface must transport ions from the atmospheric pressure of the plasma to the 10 bar pressures within the mass spectrometer. This is accomplished using an expansion chamber with an intermediate pressure. The expansion chamber consists of two cones, a sample cone upon which the plasma flame impinges and a skimmer cone. The region between these is continuously pumped. 

The burner should be so arranged that the flame impinges upon the side of the flask in such a way as to dissolve the sodium iodide from the top downward. The flask should be shaken or swirled frequently during the onset of boiling. A small amount of white solid remains undissolved even at reflux. 

Application of heat to a flammable liquid (e.g. due to radiation or flame impingement in a fire, or because of hot work ) can generate a flammable vapour-air mixture. 

Fire tests on building materials and structures. Part 12 Method of test for igmtability of products by direct flame impingement. Replaced BS 476 Part 5 1979 AMD 1 Fire tests on building matenals and structures. Part 20 Method for determination of the fire resistance of elements of constiaiction (general principles) (AMD 6487) dated 30 April 1990. Replaced BS 476 Part 8 1972... 

Valves in the inlet, seal water and pilot gas lines should be located according to permissible radiant heat densities for personnel (refer to the last section of this chapter for specific guidelines). Piping to the burning pit should be suitably protected against flame impingement (e.g., by installation below grade). 

Naphtha vapor from a relief valve on a town gas plant in the UK was ignited by a flare stack. The flame impinged on the napththa line, which burst, starting a secondary fire [7]. 

The pressure and temperature of a container s contents at the time of failure will depend on the cause of failure. In fire simations, direct flame impingement will weaken container walls. The pressure at which the container fails will usually be about the pressure at which the safety valve operates. This pressure may be as much as 20 percent above the valve s setting. The temperature of the container s contents will usually be considerably higher than the ambient temperature. 

Departure from nucleate boiling (DNB), perhaps as a result of flame impingement or other overheating effect... 

High gas velocity may cause flame impingement and impingement erosion, generally within the second- and third-pass tubes or at the back arch of return tubes. The tubes may blister and deform through overheating (but rarely collapse). 

D. Durox, T. Schuller, and S. Candel. Self-induced instability of premixed jet flame impinging on a plate. Proceedings of the Combustion Institute, 29 69-75, 2002. 

Operating personnel are to be located at a distance from the shield that assures their exposure is less than the heat flux determined by the above equation. In addition, the upper torso of an operator s body shall not be subjected to any visible fire or flame. Flame impingement upon the lower portion of the body may be permitted provided that the heat flux specified above is not exceeded. 

In normal atmospheric conditions, fire usually is initialed by a combustible material coming in contact with a heat source. The spread of fire occurs due to direct flame impingement or the transfer of heat to the surrounding combustible materials. Heat transfer occurs by three principal mechanisms - conduction, convection, and radiation. Conduction is the movement of heat through a stationary medium, such as solids, liquids or gases. Steel is a good conductor of heat as is aluminum, therefore they can pass the heat of a fire if left unprotected. 

The activation points should be located a minimum of 8 meters (25 ft.) away from a high process hazard location but not more than 5 minutes away from any location within the facility. 5 minutes is taken as the maximum allowable time since historical evidence indicates process vessel rupture may occur after this time period from flame impingement. If risk analysis calculations demonstrate longer vessel rupture periods are expected, longer time periods may be acceptable. 

The reformer tubes typically operate at maximum temperatures of 1,600°F to 1,700°F and are designed for a minimum stress-to-rupture life of 100,000 operating hours. A 35/25 Ni/Cr alloy is used that is modified with niobium and microalloyed with trace elements such as titanium and zirconium. Smaller tube diameters provide better heat transfer and cooler walls. This reduces tube and fuel costs and increases tube life. But more tubes increases the pressure drop. The optimum inside tube diameter is 4 to 5 in. The wall thickness may be as low as 0.25 inch with a length of 40 to 45 ft. The lane spacing between tube rows must be enough to avoid flame impingement from the burners. Typical spacing is 6 to 8 feet. 

Steel, aluminum, concrete, and other materials that form part of a process or building frame are subject to structural failure when exposed to fire. Bare metal elements are particularly susceptible to damage. A structural member undergoes any combination of three basic types of stress compression, tension, and shear. The time to failure of the structural member will depend on the amount and type of heat flux (i.e., radiation, convection, or conduction), and the nature of the exposure (one-sided flame impingement, flame immersion, etc.). Cooling effects from suppression systems and effects of passive fire protection will reduce the impact. 

---