Splash plate nozzle

Sarchami A, Ashgriz N, Tran HN, An atomization model for splash plate nozzles, AICHE J. 56(4), 849-857, 2009. 

Fig. 10.10 Different spray formation observed by increasing the temperature above the flashing temperature for water in Splash-Plate nozzle...

Abstract Prediction of droplet size and velocity distribution produced by splash plate requires information on the liquid sheet characteristics and its breakup process. This chapter focuses on the sheet produced by splash plate nozzles and their characteristics such as sheet breakup length and produced droplet size. It explains different flow regimes occurring in splash plate nozzles as well as various breakup lengths provided by different researchers. Sheet formation phenomenon is explained theoretically and at the end correlations for droplet size prediction are provided. 

Keywords Breakup length Droplet size distribution perforation Splash plate nozzle Stability Thickness... 

Fig. 31.1 Schematic of a splash plate nozzle [1, 25, 31] [Courtesy of TAPPI Press] [Courtesy of Springer] [Courtesy of MP. Fard et al.]...

Fig. 31.2 Effect of the viscosity on break-up regime at different values of flow velocity using a splash-plate nozzle with 1.0 mm diameter [25]. [Courtesy of Springer]...

In order to predict the size of the droplets that form from splash plate nozzles, it is necessary to characterize the liquid sheet, namely its velocity and thickness distribution [4]. There are different theoretical, numerical and experimental studies on the liquid sheet formation. These studies include both jet impingement on a wall and jet on jet impingement. 

A review of the past literature on the available correlations on the mean droplet size produced by splash plate nozzles shows that there are large discrepancies between the results. The prediction of the droplet sizes generated by splash plate nozzles is based on the Kelvin-Helmholtz (K-H) instability theory for a liquid sheet. Dombrowski and Johns [14], Dombrowski and Hooper [18] and Fraser et al. [13] developed such a theoretical model to predict droplet sizes from the breakup of a liquid sheet. They considered effects of liquid inertia, shear viscosity, surface tension and aerodynamic forces on the sheet breakup and ligament formation. Dombrowski and Johns [14] obtained the following equation for droplets produced by a viscous liquid sheet ... 

This correlation was developed for splash plate nozzles used in Kraft recovery boilers. These boilers are used in the pulp and paper industry to bum black liquor, a by-product of paper making. Black liquor is a very viscous liquid and its viscosity is a strong function of temperature. Therefore, its viscosity is easily changed by changing the liquor temperature. They used splash plate nozzles with diameters of 8.5 and 9.5 mm, and the viscosity of black liquor was changed from 50 to 200 mPa s. Note that the drop diameter relates to viscosity as d oc... 

Helpio and Kankkunen [16] measured the droplet sizes for a splash plate nozzle with diameter 15-27 mm, and used black liquor as the fluid with viscosities up to 65 mPa s. They reported the following correlation ... 

Inamura and Tomoda [28], and Inamura et al. [2] investigated the behavior of liquid sheet generated by impingement of a liquid jet onto a solid wall. They [2] combined Dombrowski s model of sheet breakup with the sheet thickness model developed based laminar boundary-layer analysis to predict the droplet size. However, they did not provide any correlation for droplet size. Fard et al. [10] studied numerically the effect of liquid properties and nozzle geometry on the droplet size distribution produced by splash plate nozzle. Again, no correlation to relate the droplet size with the studied parameters was provided. 

To conclude, there are large discrepancies among the reported correlations on the droplet size for splash plate nozzles. The theoretical predictions show that dmm OC p yet the results obtained from actual industrial nozzles show a viscosity dependency of d m oc to oc... 

Table 31.1 Correlations for median droplet size in splash plate nozzles...

A model for the atomization and spray formation by splash plate nozzles is developed by Sarchami et al. [30]. This model is based on the liquid sheet formation theory due to an oblique impingement of a liquid jet on a solid surface. The continuous liquid sheet formed by the jet impingement is replaced with a set of dispersed droplets. The initial droplet sizes and velocities are determined based on theoretically predicted liquid sheet thickness and velocity. A Lagrangian spray code is used to model the spray dynamics and droplet size distribution further downstream of the nozzle. 

The procedure begins with droplets injection right from the nozzle with the diameter equal to the splash plate nozzle diameter. The injected droplets hit the splash plate and break into several smaller droplets. Figure 31.8 shows side view of the splash plate atomizer at the time of injection. Each droplet at any specific trajectory has a specific velocity and size, equal to the sheet thickness and velocity at that trajectory (i.e., azimuthal angle). The model intends to substitute the smooth fluid sheet on the plate with discretized droplets having the same diameter (thickness) and velocity as the sheet. While droplets move further downstream, they interact with the surrounding gas and each other. Droplets will break, coalesce. 

A. Sarchami Modeling of sprays produced by splash plate nozzles. MASc. Thesis, University of Toronto (2007). 

N. Obuskovic, and T. N. Adams Fluid sheet thickness and velocity at the tip of a black liquor splash plate nozzle. Chemical Engineering Communications. 104, 1-20 (1990). 

D. Levesque, M. P. Fard, S. Morrison and B. L. Spray Understanding the effects of black liquor properties and splash-plate nozzle configuration on spray characteristics. Pulp Paper-Canada. 106 (10), 34-39 (2005). 

A. Kankkunen, T. Helpio, and P. Rantanen Small scale measurements of black liquor spraying with splash plate nozzles. TAPPI Engmetaing Crarftaence Proc., TAPPI Press, Atlanta, pp. 207-214 (1994). 

M. Ahmed, N. Ashgriz, H. N. Tran Break-up length and spreading angle of liquid sheets formed by splash plate nozzles. Journal of Fluid Engineering, 131, 1-9. 

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