EinfluBgroBen der SchichtkristallisationDie Geschwindigkeit, mit der Kristallschichten an gekuhlten Flachen wachsen, hangt im wesentlichen von dem aufgepragten Temperaturfeld ab. Sie kann bei Kenntnis der Warmeleitfahigkeit der ausfrierenn = 50 rn1n-l v =O,lOrnm/rnin CV,K lCv,m= 0,370 laRt sich dann fur eine einheitliche Beschreibung heranziehen, wenn experimentell nachgewiesen werden kann, daR die zunachst unbekannte dimensionslose Konzentrationsanderung in der laminaren Unterschicht AC/ACmaX ebenfalls eine Funktion der entsprechenden Variablen ist. Experimenteller Nachweis

Product properties and process engineering. The properties of solids are determined by their chemical composition, their state of dispersion, and their interfacial forces. They are largely responsible for the behaviour of the products during the manufacturing process and for the desired quality characteristics of the finished product. The aim of this survey is to illustrate the influence of particle size distribution and interfacial forces on product properties. The effects shown can be explained with the aid of a few physical modes. The first part shows how product properties can be adjusted to achieve a particular aim, principally by modifying the particle size. These include product‐relevant properties such as filtration properties, miscibility, and potential for dust explosion, as well properties relevant to the (final) product such as colour and taste. As the particle size decreases, the forces acting between the particle become increasingly important. The second part of this article therefore focuses on those product properties which can be influenced by way of changes in the cohesive forces. Production‐relevant properties are flow properties, bulk density, agglomeration behaviour; product‐relevant properties are tablet stability and redispersibility of foods, dyes, etc. Among the cohesive forces, capillary forces deserve particular attention. The paper concludes with an account of their role in the manufacture and use of solids. The pore structure of an agglomerated solid is determined by capillary forces and the external forces required during the manufacturing process.

Die Grundlagen zur Auslegung von Schichtkristallisationsverfahren werden mitgeteilt. Ein besonderer Schwerpunkt ist hierbei die Ermittlung des erforderlichen Energiebedarfs. Wahrend des Ausfrierens der Kristallschichten muB ein Vielfaches der Kristallisationswarme ab-und beim anschlieflenden Aufschmelzen wieder zugefuhrt werden. Daher sind diese -taktweise durchgefiihrten -Verfahren nur bei sorgfaltiger apparativer Gestaltung und ProzeBfiihrung konkurrenzfahig zu anderen thermischen Trennverfahren, bei denen eine kontinuierliche Gegenstromfahrweise realisiert werden kann.Melt crystallization -Theoretical presumptions and technical limitations. The fundamentals of the design of melt crystallization processes on cooled surfaces are presented. Determination of the energy requirement is the essential point. During each freezing step a multiple of the heat of solidification must be removed and must be re-introduced during the subsequent melting step. Consequently, discontinuous processes of this nature can only compete with other thermal separation techniques -in which a continuous countercurrent operation can be realised -if the plant is well designed and the process is precisely controlled. I Einleitung

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Formation of solids by crystallization and precipitation. Formation of solids from solutions can take place by crystallization or precipitation. The principal factor is the relationship between solubility and supersaturation. In crystallization, the solubility of the crystallising substance is so high that the formation of solids occurs largely in the metastable zone in the immediate vicinity of the solubility limits. Crystal growth and nucleation are functions of supersaturation. If a high supersaturation is required at low substance-specific growth rates for an adequate crystal growth, high nucleation rates and hence small crystals will result. On this basis, the authors present information for the specific design of crystallization processes. In contrast, the solubility of the precipitated product must be very low for precipitation. Direct crystal formation is possible only for substance systems of high solubility. As a rule, however, the precipitated substance is so insoluble that solids are formed via amorphous intermediates. The results of a large number of experiments show the influence of various parameters of the precipitation process on the filtrability of the precipitated product.