Plain-jet atomizers

The influence of liquid density on the mean droplet size is relatively small but complex. An increase in liquid density may reduce the mean droplet size due to a decrease in sheet thickness at the atomizing lip of a prefilming atomizer, or due to an increase in the relative velocity between liquid and air for a plain-jet atomizer. However, increasing liquid density may also increase the mean droplet size because a liquid sheet may extend further downstream of the atomizing lip of a prefilming atomizer so that the sheet breakup may take place at lower relative velocity between liquid and air. 

Figure 3.2 Plain-jet atomizer for the dispersion and partial oxidation of polyolefins.9...

The flow characteristics inside Hquid atomizers have been studied by numerous investigators (4—8). Of special interest to designers is the work reported on swid atomizers (4), fan spray atomizers (6,7), and plain jets (8). The foUowing discussion focuses on the flow characteristics of a swid atomizer. 

Two-Fluid Atomization Air-Blast Plain-Jet 15-130 [79]-[82] Industrial gas turbines Simple, cheap, good atomization Narrow spray angle. Atomizing performance inferior to prefilming air-blast type... 

Another important application of plain-orifice atomizers is jet engine afterburner injectors. The fuel injection system typically consists of one or more circular manifolds supported by struts in a jet pipe. The fuel is supplied to the manifold by feed pipes in the support struts and sprayed into the combustion zone through the orifices in the manifold. Increasing the number of orifices and/or using a ringlike manifold may promote uniform distribution of liquid. To reduce the risk of blockage of orifices, a minimum orifice size of 0.5 mm is usually regarded as practical for kerosene-type fuels. 

Table 4.3. Correlations for Mean, Minimum and Maximum Droplet Sizes Generated in Pressure Jet Atomization by Plain-Orifice Atomizers... 

Various correlations for mean droplet size generated by plain-jet, prefilming, and miscellaneous air-blast atomizers using air as atomization gas are listed in Tables 4.7, 4.8, 4.9, and 4.10, respectively. In these correlations, ALR is the mass flow rate ratio of air to liquid, ALR = mAlmL, Dp is the prefilmer diameter, Dh is the hydraulic mean diameter of air exit duct, vr is the kinematic viscosity ratio relative to water, a is the radial distance from cup lip, DL is the diameter of cup at lip, Up is the cup peripheral velocity, Ur is the air to liquid velocity ratio defined as U=UAIUp, Lw is the diameter of wetted periphery between air and liquid streams, Aa is the flow area of atomizing air stream, m is a power index, PA is the pressure of air, and B is a composite numerical factor. The important parameters influencing the mean droplet size include relative velocity between atomization air/gas and liquid, mass flow rate ratio of air to liquid, physical properties of liquid (viscosity, density, surface tension) and air (density), and atomizer geometry as described by nozzle diameter, prefilmer diameter, etc. 

Table 4.7. Correlations for Mean Droplet Sizes Generated by Plain-Jet Air-Blast Atomizers...

Abstract This chapter reviews atomization modeling works that utilize boundary element methods (BEMs) to compute the transient surface evolution in capillary flows. The BEM, or boundary integral method, represents a class of schemes that incorporate a mesh that is only located on the boundaries of the domain and hence are attractive for free surface problems. Because both primary and secondary atomization phenomena are considered in many free surface problems, BEM is suitable to describe their physical processes and fundamental instabilities. Basic formulations of the BEM are outlined and their application to both low- and highspeed plain jets is presented. Other applications include the aerodynamic breakup of a drop, the pinch-off of an electrified jet, and the breakup of a drop colliding into a wall. 

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

---