Auslegung von Einstoff‐Druckdüsen

Abstract

AbstractDesign of single substance pressure jets. The single substance pressure jet most commonly used produces liquid lamellae. These then degenerate to drops in the surrounding gas as a consequence of aerodynamic wave formation. The size of the droplets generated decreases according to Δp−1/3. Calculation of droplet size can be unified by defining a lamella number. The lamella number expresses the drop in lamella thickness with increasing jet distance relative to the diameter of the jet. The smaller the geometry‐dependent lamella number, the smaller the droplets relative to the diameter of the jet. The hollow cone jet produces the smallest lamella number and thus generates the smallest droplets. However, the liquid in the twist chamber of hollow conical jets at higher viscosities are decelerated much slower than in fan‐shaped jets. Measuring methods for determining the principal characteristics of jets are demonstrated for hollow conical and fanshaped jets. Turbulence jets, such as solid conical jets, produce droplets some 5 to 10 times larger than those in hollow conical jets at the same jet diameter and pressure. Droplet formation occurs mainly by turbulence in the jet. It is important to minimize the danger of blockage when operating jets. For this reason, preference is often given to that jet which gives the smallest droplet size for a given pressure and a given narrowest orifice diameter. This is particularly significant at droplet sizes d < 20 μm. Comparison and choice of jets is accomplished with the aid of a diagram representing the relative droplet size d32/D in terms of the jet pressure number Δp = ΔpD/σ and the Ohnesorge number. However, a characteristic field representation containing only characteristic quantities formed with the characteristic droplet size, apart from the relative droplet size, is suitable for determining the jet dimensions.