Zerstäuben von Flüssigkeiten

Atomization of liquids . The process of droplet formation can be represented quite clearly with the aid of dimensionless factors. Thus, clear distinction can be made between dripping, spluttering and atomization for the flow of a liquid through nozzles. In the first two cases laminar flow dominates; droplets of a definite size are formed. Atomization, on the other hand, is conversion of a jet in a turbulent state of flow into a fine spray of droplets covering a wide size range. The most commonly used atomization apparatus include one-and two-substance jets, rotation atomizers, and special purpose jets.     

Zerstäuben von Flüssigkeiten

Atomizing of liquids. Atomizing of liquids, i.e. the formation of droplets in a continuous gas phase or in vacuum, is accomplished in most cases by atomizer nozzles. Single substance pressure nozzles and pneumatic atomizers or air blast atomizers are alternative devices for that purpose. The physical facts of the partition process of the liquid and two phase flow conditions are now better known thanks to recent investigations. This permits estimation of the effect of the most important parameters on the median drop size by equations of physically based dimensionless groups. The different methods referred to in the literature for determining drop sizes lead to different results and therefore still represent a problem. Nevertheless, an attempt is made to give simplified and physically sound equations for estimating droplet size for the most important kinds of atomizers. They provide the user with an overview of the principal influencing factors and should facilitate choice of a suitable atomizer. Besides the frequently applied methods for drop and spray formation, other processes are also described which are used in special cases.     

Das Zerstäuben als Grundverfahren

Atomization as a unit process. Liquid atomization can be classified by three successive steps: disintegration; multiphase flow in the spray; and impact of droplets on the substrate. The most important process parameter is the size distribution of the droplets. By means of this parameter the liquid disintegration process can be related to the different transport phenomena in the spray or to the impacting process. The size distribution of the droplets is not a static parameter but an evolving result of local changes depending on sifting effects, on strand formation, on coalescence, on evaporation, on drying or chemical reaction processes. It is thus essential, for further analysis, to start from local instead of integral size distributions. This will be possible because of the efficiency of new particle sizing instruments with high spatial or temporal resolution. This opens the possibility for differential instead of integral balance. From this one can derive, for the future, higher precision of apparatus design and improved optimization procedures for process design. Finally, appropriate measuring techniques are discussed with regard to their special applicability to liquid atomization analysis.     

Das Zerstäuben metallischer Schmelzen

Atomization of metallic melts. Among the numerous atomization techniques for melt spraying the principal ones are described and discussed in regard to their design criteria and operating conditions. They can be classified according to the forces acting on the melt stream via the high energy fluid streams (gas or water jets), by ultrasound-activated vibrations, by impact on by rotating elements. The equations for overall drop size distributions will be discussed. This information is important for optimized production of powders, especially if the median diameters of the resultant particle size distributions are correlated with the operating parameters of the disintegration process. However, this message remains insufficient if no information is given about its standard deviation with regard to the typ of distribution.     

Begasen von niedrigviskosen Flüssigkeiten

Gassing of low-viscosity liquids . The gassing of low-viscosity liquids is a basic operation frequently encountered in practice; various kinds of apparatus have been developed depending upon the gas load. Of particular importance are the stirred tank and the bubble column because most chemical reactions in the gas/liquid system are performed in these apparatus. This paper is therefore concerned with basic chemical engineering data essential for optimum design of such equipment. Particular attention is devoted to questions of minimum gas throughput. energy requirements, and attainable mass transfer, a distinction being drawn between coalescing and non-coalescing conditions.     

Wirtschaftliches Aufheizen von Flüssigkeiten mit Hilfe von Dampfstrahl-Anwärmern

Economic Heating of Liquids Using Steam Jet Heaters In the processing of fats and oils many processing steps involve heating. Several examples given include heating of oilseed cookers, rendering of fat-bearing materials in cookers, heating of driers, heating of flow-type and stirred tanks, and direct heating of liquids. Heat transfer is accomplished, either indirectly from a medium at a higher temperature via a heat exchange surface or directly to the product to be heated. The heating capacity must be adjusted to ensure the desired temperature for the respective course of reaction. During this process, the flow of heat to be transferred can vary strongly. Therefore, the flow of steam added to a system must be adjusted with the aid of a vapour pressure regulator. A new type of steam jet heater features such a high regulating capability.