Monodisperse spray

An attractive feature of rotary atomization is the nearly uniform droplets produced with small disks at high rotational speeds and low liquid flow rates. Therefore, rotary atomization is probably the most generally successful method for producing moderately monodisperse sprays over a wide range of droplet sizes. The mean... 

In an evaluation of various techniques for droplet generation,1[88] periodic vibration of liquid jet, spinning disk and ultrasonic atomization techniques have been rated as the most appropriate methods for producing monodisperse sprays. These techniques were found to be very effective and appeared promising for refinement,... 

However, a monodisperse spray seldom exists in reality and is difficult to produce, although it can be defined mathematically as a spray consisting of droplets of the same size. Hence, a monodisperse spray usually refers to a spray in which droplets are very narrowly distributed. However, it is merely a relative term since a droplet size distribution that is sufficiently narrow in one application may be... 

Since the satellite drops constitute only a small proportion of the total liquid flowrate, a cup operating under these conditions effectively produces a monodisperse spray. Under these conditions the drop size from sharp-edged discs has been given by Walton and... 

The measure of escaping tendency for a monodisperse spray of one component droplet is... 

Greenberg, J. B., Albagu, D. Tambour, Y. 1986 An opposed jet quasi-monodisperse spray diffusion flame. Combustion Science and Technology 50, 255-270. 

Essentially, three major types of atomizers are used in practice (1) rotary wheel (or disk) atomizers, (2) pressnre nozzle, and (3) two-fluid nozzle. Figure 23.20 shows some typical atomizer designs. Ultrasonic and electrostatic atomizers can also be used for special applications to produce monodisperse sprays, but they are very expensive and low capacity. Most spray dryers operate at slight negative pressnre. New designs with low-pressure chambers enhance drying rates at lower temperatnres to dry heat-sensitive products. 

A.M. Ganan-Calvo, Generation of steady liquid microthreads and micronsized monodisperse sprays in gas streams, Physical Review Letters, 80, 285-288, (1998). 

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). 

With reference to the arguments of flame penetrating into a spray discussed above, the type of inner flame extending from the flame holding location can be classified as shown in Fig. 14.7. A monodispersed spray issued at a uniform speed is considered for simplicity. Each macroscopic flame tends to propagate normal to the spray stream. A difference from the one-dimensional flame propagation problem... 

Keywords Discrete polydisperse spray Electric droplet charging Extension nozzle Ink-jet printing Monodisperse droplet stream Monodisperse spray Multihole orifice Modulated jet excitation Nozzle hole shapes Rapid prototyping Rayleigh-type jet break-up Solder ball production... 

An early attempt to establish a device that produces monodisperse sprays is due to Dabora [21 ]. He proposed to use the principle of liquid jet formation by capillary tubes for producing a spray generator by mounting more than one capillary needle in the nozzle plate of the spray generator. Devices with 9-25 needles were realized. Internal diameters of the needles varied between 150 and 500 pm. Vibrations... 

Fig. 26.6 Monodisperse spray generator by Brenn et al. [22]. Liquid feed from the top, drainage line at the left-hand side on top of the conical distribution chamber. The jets emerge from the nozzle plate vertically downwards. Two nozzle plates tested exhibit 613 holes each, with hole diameters of 41 and 76 pm (photograph LSTM of the University of Erlangen-Numberg,...

G. Brenn, F. Durst, C. Tropeai Monodisperse sprays for various purposes - their production and characteristics. Part. Part. Syst. Charact 13,179-185 (1996). 

K.-J. Choi, B. Delcorio Generation of controllable monodispersed sprays using impulse jet and charging techniques, Rev. Sci. lustrum. 61, 1689-1693 (1990). 

Notice that, even with Vr > 2 V, the steps in Figure 4 are relatively broad, with Ap/p 7%. This result, however, does not reflect the resolution limit of our impactor, but rather the size spread of this particular PSL hydrosol. The actual resolution of the impactor would lead to Ap/p values between 1 and 2% with really monodisperse sprays, as confirmed with singly and multiply charged PSL particles 0.3 microns in diameter. 

Fig. 19.20 Velocity (a, b) and temperature (b) profiles on the spray axis for monodisperse spray simulations...

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