Pressure atomization

Figure 4 shows a three-dimensional distribution of the Sauter mean diameter, measured 38.1-mm downstream from the nozzle using a Delavan 1 GPH-80°A pressure atomizer. The operating pressure was 690 kPa (100 psi). TypicaUy, the mean diameters graduaUy increase with an increase in radial... 

Equation 14 indicates that Hquid pressure has a dominant effect in controlling the mean droplet sizes for pressure atomizers. The higher the Hquid pressure, the finer the droplets are. An increase in Hquid viscosity generally results in a coarser spray. The effect of Hquid surface tension usually diminishes with an increase in Hquid pressure. At a given Hquid pressure, the mean droplet size typically increases with an increase in flow capacity. High capacity atomizers require larger orifices and therefore produce larger droplets. 

Combustion. The primary reaction carried out in the gas turbine combustion chamber is oxidation of a fuel to release its heat content at constant pressure. Atomized fuel mixed with enough air to form a close-to-stoichiometric mixture is continuously fed into a primary zone. There its heat of formation is released at flame temperatures deterruined by the pressure. The heat content of the fuel is therefore a primary measure of the attainable efficiency of the overall system in terms of fuel consumed per unit of work output. Table 6 fists the net heat content of a number of typical gas turbine fuels. Net rather than gross heat content is a more significant measure because heat of vaporization of the water formed in combustion cannot be recovered in aircraft exhaust. The most desirable gas turbine fuels for use in aircraft, after hydrogen, are hydrocarbons. Fuels that are liquid at normal atmospheric pressure and temperature are the most practical and widely used aircraft fuels kerosene, with a distillation range from 150 to 300 °C, is the best compromise to combine maximum mass —heat content with other desirable properties. For ground turbines, a wide variety of gaseous and heavy fuels are acceptable. 

Liquid fuel is injected through a pressure-atomizing or an air-blast nozzle. This spray is sheared by air streams into laminae and droplets that vaporize and bum. Because the atomization process is so important for subsequent mixing and burning, fuel-injector design is as critical as fuel properties. Figure 5 is a schematic of the processes occurring in a typical combustor. 

Fig. 9. (a) Pressure atomizers (b) rotary atomizer and (c) twin-fluid atomizers (89,90). 

Mercury from cinnabar ore 225 tons ore/day (95% recovery) (2) 18,0 ft. diam, 8 hearth furnaces Furnaces fired on hearths 3 to 7, inclusive retention time of 1,0 hr, furnaces are oil-fired with low-pressure atomizing air burners all air, both primary and secondary, introduced through the burners draft control by Monel cold-gas fans downstream from mercury condensers. 

Spray characteristics of pressure nozzles depend on the pressure and nozzle-orifice size. Pressure affects not only the spray characteristics but also the capacity. If it is desired to reduce the amount of liquid sprayed by lowering the pressure, then the spray may become coarser. To correct this, a smaller orifice would be inserted, which might then require a higher pressure to produce the desired capacity, and a spray that would be finer than desired might result. Multiple nozzles tend to overcome this inflexible charac teristic of pressure atomization, although several nozzles on a diyer complicate the chamber design and air-flow pattern and risk collision of particles, resulting in nonuniformity of spray and particle size. 

The second, additive term carrying the viscosity impact in Eq. (14-199) is small at viscosities around 1 centipoise but can become controlling as viscosity increases. For example, for air at atmospheric pressure atomizing water, with nozzle conditions. 

FIG. 27-25a Common types of atomizers pressure atomizers. From Lefeh- ore. Atomization and Sprays, Hemisphere, New York, 1.98.9. Reproduced with permission. All rights reseroed. )... 

A. Milchev, K. Binder. Osmotic pressure, atomic pressure and the virial equation of state of polymer solutions Monte Carlo simulations of a bead-spring model. Macromol Theory Simul 5 915-929, 1994. 

Temperature 298.150 Kelvin. Pressure Atom 1 has atomic number 6 and mass Atom 2 has atomic number 8 and mass... 

The HWCVD deposition process is more or less the same as for PECVD, and was described in Section 1.7. Important differences between the two is the absence of ions, and the limited number of different species present in the gas phase, in the former. At low pressure atomic Si is the main precursor. This yields void-rich material with a high microstructure factor. Increasing the pressure allows gas phase reactions with Si and H to create more mobile deposition precursors (SiH3), which improves the material quality. A further increase leads to the formation of higher silanes, and consequently to a less dense film. 

Air-Atomized Spray Airless Spray Pressure-Atomized Electrostatic Spray... 

The cost savings in 2007 USD for airless spray and pressure-atomized electrostatic spray are as follows14 ... 

Pressure Atomization Plain- Orifice 25-250 Diesel engines, Jet engine afterburners, Ramjets Simple, Rugged, Cheap Narrow spray angle, Solid spray cone... 

In air-assist atomization, air is needed usually to augment the atomization process only at low liquid flow rates when the pressure differential is too low to produce satisfactory pressure atomization. In some designs, however, air assistance may be required over the entire range of operating conditions if the atomization quality achieved with a pressure atomizer alone is always poor. In an air-assist atomization process, the impingement of a low-velocity liquid stream by a high-velocity air stream may occur either within or outside the... 

Pressure Atomization 50-500 Standard deviation 1.4 Sn, Pb, Sb, Bi, In, Mg, Al, Zn — -17 — Narrow size distribution High EE Limited to low melting point metals... 

The decrease in the mean droplet size with increasing liquid injection pressure may be attributed to two effects. First, the high pressure-drop across the exit orifice makes the process more like a pressure atomization at high pressure. Second, the liquid is squeezed into fine ligaments as it flows through the injector orifice, and the ligaments are shattered into small droplets by the explosion downstream of the nozzle exit. 

The power requirement for pressurizing atomization gas may be estimated using the following expression ... 

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