Impingement angle

Mullis (M10), Bastress (B4), and Carlson and Seader (Cl) have conducted experimental studies to determine the heat-transfer characteristics of typical rocket-exhaust igniters. In these studies, the total rate of heat transfer to the propellant or simulated propellant surface was measured as a function of mass flow rate, geometry, and impingement angle between the igniter exhaust... 

External-mixing air-assist atomizers. Derived from ethanol (glycerin)-air spray data with initial thickness of flat circular sheet up to 0.7 mm and varied air impingement angles Sampled with oil-coated slides... 

Figure 8.12 illustrates a solid particle impinging on a surface. It has been found that the erosive wear rate depends upon the impingement angle, a, the particle velocity, vq, and the size and density of the particle, as well as the properties of the surface material. It has also been found that there is a difference in erosive wear properties of brittle and ductile materials. The maximum erosive wear of ductile materials occurs at a = 20°, whereas the maximum erosive wear for brittle materials occurs near a = 90°. Since the impingement angle is probably lower than 90° for these type of flow situations, we might consider only brittle materials, such as ceramics for this application. Let us examine brittle erosive wear in a little more detail first. 

Steady state erosion rates of all target materials eroded by SiC particles at impingement angles of 30° and 90°. Solid bars labeled I and II indicate the erosion rates of material SN-C corresponding to 30° erosion in the direction perpendicular and parallel, respectively, to the whisker orientation. 

Effect of impingement angle on erosive wear of polyurethanes. 

Walker and Bodkin (1993) discuss the advantages and limitations of a number of the commonly used erosive wear testers. The influence of particle size and shape are very important as well as the impingement angle and concentration of the slurry. They found that the wear rate increases with the jet velocity to the power of 2.2 (Mens and de Gee (1986) gives 2.8-3.2.). Wear rate is at a maximum at 30° impingement angle. The mechanism is mainly cutting. The rate increases with the size of the particle. 

The outer row of nozzles should be set fairly close to the vessel wall with a shallow impingement angle. 

Lefebvre [1] has compiled droplet size correlations for variety of spray nozzles. The present chapter extends the same compilation to include more recent correlations. The correlations provided are by no means exhaustive, yet they provide commonly used correlations. These correlations are provided in Tables 24.1-24.12 at the end of this chapter. The correlations are mainly based on the (i) fluid properties (mainly density, viscosity, and surface tension), (ii) nozzle geometry, such as the exit orifice diameter, impinging angle of the air on the liquid, etc., and (iii) operational parameters such as the flow rates of the liquid or gas. While some experiments have been conducted to consider the effects of all these three types of variables, many simply choose only to deal with a handful of them, and neglect the effects of others. Obviously, the more the experimental variables, the more difficult it is to obtain an accurate correlation for the droplet size. 

This process is sketched in Fig. 30.2. To clearly describe the spray characteristics of the impinging jets, related parameters include impingement angle (20), jet velocity U), and jet radius and diameter (27 = D), position angle (f)), and sheet thickness, h. 

Figure 30.3 (picture 4) shows waves on the sheet, which are also referred to as impact waves. These are high-frequency circumferential waves that dominate the sheet breakup at high impingement angles and velocities. The impact waves control the breakdown of the sheet over a wide range of ambient air densities, particularly below the atmospheric. Dombrowski and Hooper [11] found a critical value of... 

The value of P is determined by the impinging angle and can be numerically calculated from (30.14). Another expression for the sheet shape is now provided by dividing (30.13) by (30.6) ... 

Figure 30.9 presents the theoretical (30.19 and 30.21) and experimental results of sheet breakup length and width versus We [23]. The three vertical dotted lines are the demarcation lines between the closed-rim sheet and open-rim sheet. The open-rim sheet is measured mily for the case of 0 = 120. A favorable agreement can be seen in Fig. 30.9 for liquid sheets with closed rims, which shows that the breakup width is linearly proportional to We. The slope of the linear relatimi is determined by the impinging angle. Figure 30.10 also shows that the breakup width increases... 

Fig. 30.10 Breakup length and width versus impinging angle [23] (Courtesy of the American Institute of Physics)...

FIGURE 8. Effect of test temperatures on the erosion rate at a fixed impingement angle of 75°. 

The effect of ultra-high molecular weight poly-(ethylene) (UHMWPE) the on mechanical and solid particle erosive wear behavior of aramid fabric reinforced-epoxy composites has been investigated [64]. A siUca sand of a size of 150-280 fim was used as an erodent. The erosive wear rate of UHMWPE in aramid-epoxy composite exhibits a lower value in comparison to neat composites. A maximum erosion rate was observed at an impingement angle 60 , and the material behaves in a semiductile manner. 

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