Reynolds number, droplet

R. B. Peterson Characterization of a simple, high Reynolds number droplet generator for combustion studies. Review of Scientific Instruments, 59(6), 960-966 (1988). 

To the extent that radiation contributes to droplet heatup, equation 28 gives a conservative estimate of the time requirements. The parameter ( ) reflects the dependence of the convective heat-transfer coefficient on the Reynolds number ... 

Droplet trajectories for limiting cases can be calculated by combining the equations of motion with the droplet evaporation rate equation to assess the likelihood that drops exit or hit the wall before evaporating. It is best to consider upper bound droplet sizes in addition to the mean size in these calculations. If desired, an instantaneous value for the evaporation rate constant may also be used based on an instantaneous Reynolds number calculated not from the terminal velocity but at a resultant velocity. In this case, equation 37 is substituted for equation 32 ... 

A droplet Nusselt number = 2, corresponding to pure conduction (Reynolds number = 0) to infinity, is employed for evaluating the coefficient of heat transfer. 

Note that the absolute value of Pp - p has been assumed. The negative value of this difference indicates that the droplet displacement is centripetal. The value of the Reynolds number corresponding to Ar = 3650 from Figure 10 is 45. Hence we can determine the radial settling velocity from the definition of the Reynolds number ... 

Fig. 14 shows the comparison of the photographs from Chandra and Avedisian (1991) with simulated images of this study for a subcooled 1.5 mm n-heptane droplet impact onto a stainless-steel surface of 200 °C. The impact velocity is 93 cm/s, which gives a Weber number of 43 and a Reynolds number of 2300. The initial temperature of the droplet is room temperature (20 °C). In Fig. 14, it can be seen that the evolution of droplet shapes are well simulated by the computation. In the first 2.5 ms of the impact (frames 1-2), the droplet spreads out right after the impact, and a disk-like shape liquid film is formed on the surface. After the droplet reaches the maximum diameter at about 2.1ms, the liquid film starts to retreat back to its center (frame 2 and 3) due to the surface-tension force induced from the periphery of the droplet. Beyond 6.0 ms, the droplet continues to recoil and forms an upward flow in the center of the... 

Figure 3.15. Spreading behavior of a single droplet impinging on flat (e/D0 = 0) and non-flat (e ID0 = 0.33, XID0 =2.8) surfaces at different Reynolds numbers (We = 2000) (Reprinted from Ref. 389, 1995, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X51GB, UK.)...

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]... 

Resistance functions have been evaluated in numerical compu-tations15831 for low Reynolds number flows past spherical particles, droplets and bubbles in cylindrical tubes. The undisturbed fluid may be at rest or subject to a pressure-driven flow. A spectral boundary element method was employed to calculate the resistance force for torque-free bodies in three cases (a) rigid solids, (b) fluid droplets with viscosity ratio of unity, and (c) bubbles with viscosity ratio of zero. A lubrication theory was developed to predict the limiting resistance of bodies near contact with the cylinder walls. Compact algebraic expressions were derived to accurately represent the numerical data over the entire range of particle positions in a tube for all particle diameters ranging from nearly zero up to almost the tube diameter. The resistance functions formulated are consistent with known analytical results and are presented in a form suitable for further studies of particle migration in cylindrical vessels. 

Nu, Pr, Re — Nusselt, Prandtl, and Reynolds numbers, respectively, D — Droplet diameter,... 

The droplet number density presented in Fig. 16.4 indicates the solid-cone nature of the spray except in the immediate vicinity downstream of the nozzle exit. On the spray centerline at 2 = 10 mm, steam provides a lower number density as compared to the two air cases. This is due to the expansion of the spray jet at a relatively lower Reynolds number with steam and rapid vaporization of smaller sized droplets. At increased radial positions and 2 = 10 mm, a peak in the number density corresponds to the spray cone boundary. This peak shifts radially outwards with an increase in axial distance due to the expansion of the spray cone. Similar phenomena are observed for the normal and preheated air cases except that droplet number density for the preheated air case is much higher on the spray central axis (at r = 0). This is attributed to the effect of preheated air on atomization (i.e., larger mean droplet size and smaller number density with normal air as compared to that for heated atomization... 

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