Swirl nozzle

Swirl nozzles Nozzles used to distribute primary air into a space by creating a swirl. This arrangement provides good entrainment and mixing of the air. 

The conditions necessary for equality of particle size distribution were determined under ambient conditions. The nozzles used in the investigation can be classified as swirl-spray pressure nozzles. They accommodate a swirl insert which imparts a tangential velocity to the exiting fluid and results in a conical spray pattern. These nozzles were sufficiently different from conventional swirl nozzles (see Putnam et al., Ref. 6) to require an experimental study of particle size distribution. 

Jarmer, D.J. Lengsfeld, C.S. Randolph, T.W. Manipulation of particle size distribution of poly(-lactic acid) nanoparticles with a jet-swirl nozzle during precipitation with a compressed antisolvent. J. Supercrit. Fluids 2003, 27 (3), 317-336. 

Swirl nozzles not suitable for suspensions because of phase separation... 

Spray nozzles can be classified as twin-fluid, swirl, hydraulic, rotary, ultrasonic, electrostatic, and many more. Often a single nozzle may fall under more than one category due to its design. For example, a swirl nozzle may be based on twin-fluid swirl atomization. 

Fig. 24.37 (a) A schematic of a swirl nozzle with axial flow, (b) a schematic of a swirl nozzle with tangential flow (Courtesy of Lechler, Inc.)... 

Dual orifice or duplex swirl nozzles consist of two simplex nozzles placed inside one chamber. In the chamber, one nozzle surroimds the other, where the surrotmd-ing nozzle is called the secondary nozzle, and the inside nozzle is called the primary nozzle. The underlying idea behind a dual orifice design is that if the supply of liquid is low, it will flow entirely through the primary nozzle, and the resulting spray will not be any less diluted. Once the spray starts to increase, some of the liquid will flow through the secondary nozzle, increasing the coverage of the spray. The mechanism is outlined in Fig. 24.41. 

Fig. 24.41 The design of a typical dual-orifice swirl nozzle...

Many investigations have been done on the performance of swirl nozzles. And yet, due to the complex physics in swirl atomization, much has yet to be discovered [64]. This text attempts to compile drop size correlations for the three types of swirl nozzles mentioned, and they are shown in Table 24.7. From the correlations shown below, it can be concluded that the performance of swirl nozzles depends largely on the liquid properties, and very little on the nozzle geometry. 

Swirl nozzles are often used in twin-fluid nozzles, to enhance the overall atomization process in them. In some cases, the air is swirled before it comes in contact with the liquid. In other cases, both the air and liquid are swirled. An important design consideration in nozzles where both the hquid and gas are swirled is whether the gas should be swirled in the same direction, or in the opposite directions. Rotation in the same direction provides a strong circulation of fluid, while rotation in the opposite direction creates opposing shear forces, which helps in mixing the hquid and gas, and also in the atomization. Airblast, air-assist, and effervescent nozzles often contain swirling chambers. 

In the section on Twin-Huid Nozzles, it was shown that Lund et al. [36] derived 24.4.i for effervescent nozzles. This same equation is valid for swirl nozzles. The only difference lies in the method by which the ligament diameter is determined. A formula was derived by Couto et al. [66] 24.7.ii, and can be used in conjunction with 24.4.i. The spray angle is considered in this formula as well. Equation 24.4.i is plotted in Fig. 24.42 as a function of the Ohnesorge number at different ligament diameters. 

Lefebvre [63] derived 24.7.v for simplex swirl nozzles using a wide range of surface tensions. He equated SMD to be a function of injection pressure, mass flow rate, surface tension, and dynamic viscosity. Additionally, he also included the effect of air density. In his equation, he gave surface tension a smaller influence, and injection pressure a larger influence. 

Fig. 24.43 Comparisons between four correlations for simplex swirl nozzles with m-c = 50 g/s, AP = 1.5 MPa plotted against (a) injection pressure, (b) mass flow rate, (c) surface tension...

Park et al. [68] derived 24.7.ix for duplex swirl nozzles. It is very similar to 24.5.i-24.5.iii however it does not contain any effect of liquid mass flow rate. The formula was derived based on variations in temperature only, which caused the liquid properties to change independent changes were not applied. The correlation indicates that surface tension has a much smaller impact on SMD in duplex nozzles than simplex nozzle. It also shows that the viscosity plays a much larger role in the atomization process, while the effect of the injection pressure is the same as in simplex nozzles. Figure 24.45 plots this equation as a function of viscosity and injection pressure at various surface tensions, using AP = 300 kPa and mass flow rate = 50 g/s. As expected, an increase in injection pressure leads to a decrease in SMD, and an increase in viscosity leads to an increase in SMD. 

Orzechowski [69] derived many different formulas, not just for swirl nozzles, but rotary nozzles too. Four correlations are accredited to him in the area of swirl nozzles. The first one presented in Table 24.4, 24.7.x, is very similar to 24.7.iii-24.7.vi. Due to the absence of surface tension in the formula, it is not fair to compare it with the other four equations mentioned. 

Petela and Zajdel [73] and Zajdel [74] conducted experiments on coal slimy atomization where coal particles of diameters up to 385 pm were mixed in a solution of benzoic acid and atomized using a swirl nozzle. The experiment by Petela and Zajdel [73] was conducted on monodispersed coal particles. In their experiment, 140 atomization processes were conducted however only 74 of them were used to derive the formula given. Zajdel [74] later ciuiducted a similar experiment using polydispersed coal particles. The resulting equations, 24.7.xiv and 24.7.XV, are shown in Table 24.7. An interesting aspect about both equations is that only ratios are cmisidered instead of individual variables. It should be noted... 

A more recent study on swirl nozzles was conducted by Khavkin [64]. In his book, he went into great detail on the mechanism and theory of swirl nozzles, and presented the findings of his own research. He proposed two equations for aU swirl nozzles, 24.7.xvi and 24.7.xvii. Equation 24.7.xvi considers the effect of the liquid film thickness, while 24.7.xvii considers the effect of nozzle diameter. In both cases, Khavkin proposes that SMD is proportional to either or Three... 

Matsumoto and Takashima [83] proposed an equation for ligament formation, in which the diameter of the ligament is also considered. Equation 24.4.i for effervescent and swirl nozzles greatly resembles this correlation. 

Wang, X. F., and Lefebvre, A. H., Atomization Performance of Pressure Swirl Nozzles,... 

Nonnenmacher, S., and Piesche, M., Design of Hollow Cone Pressure Swirl Nozzles to Atomize Newtonian Fluids, Chemical Engineering Science, Vol. 55, 2000, pp. 4339-4348. 

ARl injection pressure differential across nozzle Variation in surface tension was very small in the experiments conducted Results compiled empirically from second-hand data Valid only for simplex swirl nozzles Same as above Jasuja [8]... 

Liquid used should be fuel The formula was derived based on variations in temperature only, which cause liquid properties to change independent changes to liquid properties were not applied Valid only for duplex swirl nozzles ) = 1.9 mm... 

Acts as a general equation for all swirl nozzles Conditions same as above... 

Valid only for a spill-return type of swirl nozzle Pe > 1,200... 

Abstract This chapter discusses several other types of atomizers that were not considered in the previous chapters. This includes swirl nozzles, T-jet nozzles, and vibrating mesh nebulizers. The droplet size correlations for different types of nozzles is provided in Chap. 24. 

Keywords Swirl nozzles T-jet nozzle Vibration mesh nebulizers... 

Fig. 33.1 Schematic of a simplex swirl nozzle (a) top view, (b) side view...

---