Nozzle plate

Typical cascade impactors consist of a series of nozzle plates, each followed by an impaction plate each set of nozzle plate plus impaction plate is termed a stage. The sizing characteristics of an inertial impactor stage are determined by the efficiency with which the stage collects particles of various sizes. Collection efficiency is a function of three dimensionless parameters the inertial parameter (Stokes number, Stk), the ratio of the jet-to-plate spacing to the jet width, and the jet Reynolds number. The most important of these is the inertial parameter, which is defined by Equation 2) as the ratio of the stopping distance to some characteristic dimension of the impaction stage (10), typically the radius of the nozzle or jet (Dj). 

The previous chapters have shown how screw machines are comprised of successive zones that perform specific process tasks. The most common process task is a combination of transporting materials and generating pressure. At the head of the machine, higher pressure needs to be applied, in particular, where typically an extrusion die or a nozzle plate is attached however, most mixing and kneading zones are also pressure consumers that require pressurization of the melt. 

Figure 4. Industrial gas distributors (A) perforated plate (B) nozzle plate (C) bubble-cap plate.

In eq 10, ho is the height above the grid where the bubbles form (for a porous plate, ho = 0 for a perforated plate, ho = L for a nozzle plate, ho is the height of the outlet opening above the plate and for a bubble-cap plate, ho is the height of the lower edge of the cap above the plate). 

Fig. 6.6 Results of steel sleeve tests for a new explosive with 8 and 10 mm holes in the nozzle plate.

Drop placement accuracy Exact drop landing position is uncertain, due to various parameters such as jet-to-jet variations, single jet-overtime, sensitivity to nozzle straightness, nozzle and surface wetting, nozzle plate contamination, ink formulation and condition, and drop velocity. This issue is worse for longer flight paths or "throw distance". 

One approach to prolonging the lifetime of the nozzles is to fabricate the nozzle plate from a (high performance) ceramic. Some types of the latest generation of print heads produced by Dimatix... 

Com. are eqmpped with nozzle plates made from silicon. A possible alternative are print heads with nozzle plates made from plastic (polyimide) which are offered by Xaar Com. Flexible nozzle plates may cushion the impact of the ceramic particles. For the ceramic inkjet printers commercially offered today the problem of insufficient functional life of the print heads is not solved yet. 

Micro-channel emulsification is even farther away from industrial application however, there are a few small companies offering nozzle plates that show relatively large fluxes, coming into the realm of practical feasibility. For example, fluxes of... 

Fig. 13.1 Ink-jet nozzle plate fabricated by through-mask electrochemical micromachining, Schematic of the concept top), and a photograph showing an array of nozzles bottom) [23]...

Yamazaki, K., Okamoto M., 1997. A Review of New Directions in Shingosen and Synthetic-fiber Textiles for Sportswear , Journal of The Textile Institute, 88 3,5-31. Wang, J., Zhang, C., Wang, H. et al. 2007. Air-permeable humid-conductive PTT fiber and nozzle plate used therefor , CN 2915899 Y. 

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,...

In the present section, we restrict ourselves to the version of droplet generators working with (mostly metal) nozzle plates carrying the orifice hole(s). The design of the nozzle plate concerns both the diameter and the shape of the... 

As single-hole nozzle plates, circular orifice disks, typically 200 pm thick, with the nozzle hole in the center, are equally suitable as thin metal sheets, as used, e.g., for spatial filtering in optical setups. Thicker disks are best suitable as orifice plates if the hole exhibits a tapered (inlet) region on one side and has its nominal diameter only on a short part of the plate thickness. This feature ensures low flow resistance and good directional stability of the jet. Figure 26.9 shows typical shapes of nozzle cross section profiles [41]. 

That is, a wetting agent acts to reduce the surface tension of the ink so that a more uniform surface energy on the surface of the nozzle plate is achieved. This action has been observed to minimize puddling of the ink on the surface of the nozzle plate. Wetting agents are summarized in Table 3.3. 

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