Droplet diameter impact

Fig. 10. Water droplet impacts on a flat surface. The initial droplet diameter is 2.3 mm and the surface temperature is 400 °C. We = 15.

Three different subcooled impact conditions under which experiments were conducted and reported in the literature are simulated in this study. They are (1) K-heptane droplets (1.5 mm diameter) impacting on the stainless steel surface with We — 43 (Chandra and Avedisian, 1991), (2) 3.8 mm water droplets impacting on the inconel surface at a velocity of 1 m/s (Chen and Hsu, 1995), and (3) 4.0 mm water droplets impacting on the copper surface with We — 25 (Inada et al., 1985). The simulations are conducted on uniform Cartesian meshes (Ax = Ay — Az — A). The mesh size (resolution) is determined by considering the mesh refinement criterion in Section V.A. The mesh sizes in this study are chosen to provide a resolution of CPR =15. 

The spreading behavior of droplets on a non-flat surface is not only dependent on inertia and viscous effects, but also significantly influenced by an additional normal stress introduced by the curved surface. This stress leads to the acceleration-deceleration effect, or the hindering effect depending on the dimensionless roughness spacing, and causes the breakup and ejection of liquid. Increasing impact velocity, droplet diameter, liquid density, and/or... 

Comparing Eq. (51) to Eq. (43) or Eq. (52) to Eq. (44a), it is clear that for the same liquid properties and droplet diameter at impact, splashing takes place at lower impact velocities on a liquid film than on a dry surface. 

For the deformation of droplets of normal liquids at low impact velocities on a horizontal plane surface without phase change, Tan et al)513 developed a physical-mathematical model with a droplet falling from a certain height under the influence of gravity. They derived quantitative relations for the dimensions of the deformed droplet, including the effects of initial droplet diameter, height of fall, and thermophysical properties of liquid. In this model, the behavior of droplet deformation was assumed to be governed by... 

Droplets were collected on 1-inch ethylcellulose strips, placed laterally across the wind tunnel floor at various distances downwind, and on 11-mm. glass rods located 40 inches downwind from the spray nozzle. The effective fall distance for droplets impinging on the wind tunnel floor was 2 feet. Droplet sizes that reach the glass rods will not all impact efficiently, and the efficiency varies with droplet diameter (2, 4). Nonetheless, the size droplet reaching a given glass rod was approximately... 

Splashing can be seen to begin in droplets with Weber (We) numbers of 100-1000, and fingers have been observed in droplets that have a Reynolds (Re) number of 15000 and a We of 1000. (Re = p.u.d)/iJL and We = p.u. d)fa, where p,u,d,pt and a are the liquid density, droplet impact velocity, droplet diameter, liquid viscosity, and hquid surface tension respectively.) As the drops used in inkjet printing typically have diameters below 100 microns, values of Re = 2.5—2000, and We = 2.7-1000 can be expected. 

In general, liquids should not bind to the inserts or walls they should flow as rivulets or drops along the surface of the insert. Vane separators droplet diameter >20 jm droplet concentration >0.1 mg/m Mesh pads droplet diameter 3 to 20 pm droplet concentration 0.01 to 0.1 mg/m Fiber beds designed for impaction (usually cylindrical or candles ) droplet diameter 0.2 to 3 pm droplet concentration 0.001 to 0.01 mg/m Fiber beds designed for Brownian motion (usually cylindrical or candles ) <0.1 pm droplet concentration <10 mg/m ... 

Typical heat transfer results to monodisperse sprays impacting on a heated surface are shown in Fig. 18.24. The liquid flow rate is varied over a wide range, while the droplet diameter is kept almost constant [136]. The heat flux versus surface temperature trends are similar to those of conventional boiling curves (see Chap. 15 of this handbook), and the heat fluxes are very high. The available experimental data [133, 134,137-140] show that the volumetric spray flux V (m3/m2 s) is a dominant parameter affecting heat transfer. However, mean drop diameter and mean drop velocity and water temperature have been found to have an effect on heat transfer and transitions between regimes. Urbanovich et al. [141], for example, showed that heat transfer is not only a function of the volumetric spray flux but also of the pressure difference at the nozzle and the location within the spray field (Fig. 18.25). 

Figure 14 In vitro assessment of droplet size measurement in the European Standard. Simulated patient inhalation at 15 L/min draws air over (or through) the nebulizer where entrained ambient air mixes with nebulized aerosol. A sample of the air at 2 L/min is drawn into a Marple Series 290 cascade impactor, which sizes aerosol droplets in relation to aerodynamic diameter. Impacted aerosol solute (e.g., NaF or drug) can be subsequently desorbed and quantified from each impaction stage.

Fig. 8.4 Splashing of a 2.7 mm diameter moltem tin droplet during impact with velocity 4 m/s on a stainless steel surface at temperature 240°C. The droplet and substrate are both above the melting point of tin (232°C) so there is no Ireezing [3]...

Fiber beds designed for impaction (usually cylindrical or candles ) droplet diameter 0.2-3 gm droplet concentration 0.001-0.01 mg/m. ... 

As shown in Ref. 43 the deposited volume can be deduced from the force curves measured during the deposition process. In the case of femtoliter droplets (diameter in the 1 p.m range], a sharp increase of droplet size is observed for short times (t < 2 s typically), followed by a saturation regime where prolonged contact time has no obvious impact on the liquid flow. This dynamics indicates a nondiffusive process for the liquid transfer in striking a contrast to molecule transfer in DPN and confirms the fundamental difference... 

The CFD model is employed to simulate the penetration behaviour of a cubic particle into a liquid droplet. The ratio of the cube width (a, pm) to droplet diameter (d, pm) covers 20 120, 20 240, and 20 +oo, where +oo means a flattened liquid surface. Figure 18.43 shows the 3D computational domain and the arrangement of solid particle and liquid droplet. Three different particle orientations, that is I, II. and III, are considered. Both head-on collision and off-centre collision are investigated. As in droplet-droplet collision studies [47], an impact number B is defined to describe the off-centre degree during particle-droplet collision, as follows ... 

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