Hans Rumpf

Physical aspects of comminution and new formulation of a law of comminution

Abstract A detailed description of fracture phenomena, observed in comminution experiments, is followed by the derivation of a similarity law of comminution which is based on reasonable physical assumptions. Starting from the simplifying suppositions of both geometrical similarity of the particles undergoing comminution and similarity of the states of stress and strain, a relationship is obtained between initial particle size and energy investment for a distinct material. On additional simplifying assumptions this leads to Rittingers law. With the help of dimensional analysis the similarity law is extended to cover different materials and different initial flaw distributions. The results of various comminution experiments are discussed in the light of the new comminution law.

Deformation behaviour of agglomerates under tensile stress

Abstract A new instrument has been developed in which the stress—strain behaviour of agglomerates can be measured in uniaxial tension. The instrument permits tension to be measured under predetermined stresses, and further enables the tensile stress—strain behaviour to be determined in the agglomerate in the unstable region. Agglomerates with different bonding mechanisms were studied. In the case where agglomerates are held together by liquid bridges, a model has been developed which permits the stress—strain behaviour to be predicted. This is confirmed by experiments. For agglomerates with a high degree of liquid saturation, the tensile stress—strain behaviour can be predicted from the capillary pressure relation. The tensile stress—strain curves of dry agglomerates and of agglomerates with solid bridges between particles are shown and compared. From the different stress—strain characteristics, the physical nature of the bonds can be elucidated.

Flow processes in aerated silos

Abstract To obtain an insight into the complicated processes in aerated silos, experimental results are given which were obtained using a plane model. The flow of solid material, the excess pressure, the boundary lines between the moving and static material, the distribution of the flow and the air velocity profile at the aerated floors were determined as a function of the volumetric flow of air injected into both floors. Together with comparable measurements on electrical analogue models, the results show that the comparison often made in the literature with a fluidized bed is an oversimplification.

Principle and construction of two new air classifiers for particle size analysis

Abstract Air classifiers for particle size analysis should produce extremely sharp cuts and they should allow the prediction of the actual cut size. In order to avoid systematic errors the construction should be appropriate to their function and to compete with other apparatus for particle size analysis the time required for one cut should be as short as possible. The principle and the requirements of counterflow equilibrium and transverse flow classification is discussed under these aspects and two new classifiers based on the conclusions drawn are described.

The characteristics of systems and their changes of state

Disperse systems generally consist of two or more phases. If the elements of a particulate material are separately embedded in a continuous phase called the dispersion medium, then we describe the system as discretely disperse, in contrast with disperse systems in which two continuous phases permeate each other. A continuous disperse phase is termed compactly disperse. It can also consist of elements which, although distinguishable, stick to one another or merge into one another. If, however, these elements adhere to one another without forming bridges of material, then the phase can also be termed discretely disperse. Here the designations are not clear cut.

Die trennkurven des dekantierens

Zusammenfassung Es wird gezeigt, wie sich die Trennkurven des Dekantierens sowohl im Schwerefeld wie im Fliehkraftfeld unter den Voraussetzungen des Stokesschen Gesetzes berechnen lassen. Die Trennkurven des Dekantierens im Schwerefeld wurden experimentell mit Suspensionen von Quarzstaub um 20 μm Teilchendurchmesser gepruft.

Fundamental physical processes and particle metrology

Let us consider a single particle (Fig. 3.1) suspended in a fluid at a given point in time. Its instantaneous position is determined by its orientation and the position of its centre of gravity. We shall designate its translational velocity by w and its rotational velocity by ω. In the absence of the particle the fluid at the point of time in question has a definite velocity profile with a velocity υ at the position of the centre of gravity of the particle. The relative velocity is

Zur Theorie der Zugfestigkeit von Agglomeraten bei Kraftübertragung an Kontaktpunkten

{{\upsilon }_{\text{rel}}}=\upsilon -w