Droplet impingement

Impingement demister systems are designed to intercept liquid particles before the gas outlet. They are usually constructed from wire mesh or metal plates and liquid droplets impinge on the internal surfaces of the mist mats or plate labyrinth as the gas weaves through the system. The intercepted droplets coalesce and move downward under gravity into the liquid phase. The plate type devices or vane packs are used where the inlet stream is dirty as they are much less vulnerable to clogging than the mist mat. 

Single-droplet breakup at very high velocicty (L/velocity) . This governs drop size in free fall as well as breakup when droplets impinge on solid surfaces. 

Goses with entroined liquid droplets tlow between the zig-zog bottles. The gos con eosily moke the turns while the liquid droplets impinge upon the wolls ot the baffles ond coolesce to o size such thot they drop downword, being too heovy to be corried in the gos. 

Goses with entroined liquid droplets flow between the zig-zag baffles. The gos can easily make the turns while the liquid droplets impinge upon the walls of the baffles and coalesce to a size such that they drop downward, being too heavy to be carried in the gas. 

Figure 3.13. Deformation process of a single droplet impinging on a flat surface (Re = 1600, We = 26.7) (a) simulation left), experiment right), and (b) comparison between calculated and measured dimensionless diameter and height ofa flattening droplet. (Photograph Courtesy of Prof. Dr. Jiro Senda at Doshisha University, Japan. Experimental data reprinted with permission from Ref. 334.)...

Figure 3.14. Deformation process of a single droplet impinging on a non-flat surface (Re = 38115, We = 8474, e/D0=0.33, A/D0=2.8). From top to bottom

Figure 3.17. Deformation sequence of a single droplet impinging on a non-flat surface (Re = 76229, We = 33897, /D0= 0.33, X/D0 = 0.9). From top to bottom ...

Figure 3.22. Spreading and solidification sequence of a single droplet impinging on a flat surface Re = 867 left), Re = 4335 (center), and Re = 17340 (right).

Figure 3.23. Schematic and micrograph of spreading, breakup and solidification modes of liquid metal droplets impinging on a cold surface. (a)-(d) Pancake pattern regularly shaped disks with or without corona, (e)-(h) Flower pattern irregularly shaped platelets with or without corona. (Micrograph reprinted with permission from Ref. 403 and 407. Courtesy of Dr. J. M. Houben, Eindhoven University of Technology, Netherlands and courtesy of Dr. Seiji Kuroda, National Research Institute for Metals, Japan.)...

Figure 3.24. Classification of droplet impingement topology. (Reprinted with permission from Ref. 409.)...

In a subsequent study, Chandra and Avedisian13851 investigated droplet impingement on a ceramic porous surface. It was found that the spreading rate of a droplet on the porous surface at 22 °C is lower than that on the stainless steel surface, and for a given temperature the maximum spread diameter is smaller on the ceramic surface... 

Figure 3.27. Spreading, breakup and evaporation of normal liquid droplets impinging on a hot surface. (Photograph Courtesy of Prof. Dr. Jiro Senda at Doshisha University, Japan.)...

Al-Roub et all421 identified three basic modes of liquid breakup during droplet impingement onto a liquid film (1) rim breakup, (2) cluster breakup, and (3) column breakup. The rim breakup mode involves the breakup and ejection of one or a few small droplets at the outer edge of the film, while the cluster breakup mode involves the breakup of liquid into clusters of many small droplets at the outer edge of the film. In the column breakup mode, liquid breaks up into one or a few droplets from a column of liquid at the center of the spreading droplet as a result of the surface waves reflecting back to their source. The diameter and number of the... 

Table 4.21a. Correlations for Final Splat Diameter Created by a Droplet Impinging on a Solid Surface...

One of the earliest analytical models for the calculation of flattening ratio of a droplet impinging on a solid surface was developed by Jones.1508] In this model, the effects of surface tension and solidification were ignored. Thus, the flattening ratio is only a function of the Reynolds number. Discrepancies between experimental results and the predictions by this model have been reported and discussed by Bennett and PoulikakosJ380]... 

Further extensions of Madej ski s mod ell4011 may include (a) turbulence effect, (b) Rayleigh instability or Taylor instability and droplet breakup, (c) vibrational energy, and (d) influence of solidification on flow)514 Some issues related to the deformation and solidification of droplets on a flat substrate in splat quenching have been addressed in Refs. 380 and 514. To date, analytical models addressing droplet impingement on a semi-solid surface have not been found in available literature. 

The first numerical study on the transient flow of a single liquid droplet impinging onto a flat surface, into a shallow or deep pool was performed by Harlow and Shannon)397 In their work, the full Navier-Stokes equations were solved numerically in cylindrical... 

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