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Sorption isotherms give an insight into thermodynamic behaviour of materials during drying. This is necessary for process optimization and to prevent over-processing, especially at higher temperatures, such as in drum drying or superheated steam spray drying. Aim of this study is to introduce a simple, barometric method for the determination of water desorption isotherms. As test materials, microcrystalline cellulose and potato starch are used. Both materials show specific temperatures where the trend of the determined GAB parameters and the slope of the isosteric heat of sorption are changing significantly. Thus, is the predictability of thermodynamic behaviour depending on the material. Further, it is demonstrated that the extrapolation of low temperature sorption data (

The composition and molecular mobility within thin spherical liquid films have been investigated using nuclear magnetic resonance (NMR) diffusion measurements. These films were formed either on the surface of pores inside a sponge at low saturation or by adsorbed water on the outside of urea prills during caking. Using pulsed field gradient (PFG) NMR experiments, the molecular mobility within these liquid films was determined through analysis of the conditional probability density for displacement (propagator). Molecular diffusion coefficients were determined for films in the sponge and prill systems by fitting the experimental propagators using a model for diffusion on an array of isotropically distributed infinite planes. By comparing these diffusion coefficients with bulk diffusion coefficients for a range of concentrations of urea solutions (2.1 M, 6.2 M and saturated), it was possible to optimize the PFG experimental parameters to enable accurate determination of molecular diffusion in these spherical liquid films. Determination of the diffusion coefficients for a range of urea solutions in the sponge enabled identification of the composition of the film that formed on the surface of the urea prills. Analysis of these data showed that the liquid layers are composed of saturated urea solution covering the surface of the prills, with an estimated layer thickness on the order of 10–5 m. The shape of the propagators indicated the adsorbed water was uniformly distributed over the surface of the urea prills, rather than primarily in the meniscus between particles, which agrees with dye visualization experiments on a pair of urea prills during caking. This work provides the first quantitative measurements of diffusion in thin spherical films, which is a key parameter for determining what controls the presence and rate of bonding between adjacent particle surfaces.

A novel experimental method has been developed that enables the direct observation of bridge formation between urea particles under very carefully controlled climatic conditions (±

The time consolidation of bulk solids, known as “caking,” plays an important role in many industries. To investigate the bridge formation between two discrete particles under real storage conditions a new experimental setup has been designed. In this study, the aim is to predict the caking behavior of hygroscopic materials under the influence of parameters that lead to caking phenomena. With salt-like substances such as NPK fertilizer and urea, caking increases with rising humidity and temperature. A state of matter diagram for urea shows in a condensed form the results of numerous caking experiments indicating clearly the critical caking conditions.

Solidification and caking of bulk solids often occurs during storage or while being transported to the customer. To investigate the formation and growth of solid bridges between two discrete particles, the modification of the contact region between these two particles stored in a climatic chamber is examined. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge is analyzed. The objective is to describe the behavior of crystalline or salt-like granules under real storage conditions.

To investigate the formation and growth of solid bridges between urea particles, the changes in the contact region between two discrete particles are measured. The work is carried out using a Double-Particle-System (DPS). The DPS was stored in a climatic chamber. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge between these particles was analyzed. The objective was to describe the geometrical changes in the contact region and to measure the strength of the resulting interparticle bridge.

Wahrend der Lagerung oder dem Transport von Schuttgutern zum Kunden kommt es haufig zu Verfestigungen und Verbackungen. Um die Bildung und das Wachstum von Feststoffbrucken zwischen zwei Partikeln zu untersuchen, werden die Anderungen in der Kontaktregion der beiden Partikel wahrend der Lagerung in einem Klimaschrank beobachtet. Der Einfluss der Parameter Lagerdruck, Temperatur, relative Luftfeuchte und Lagerzeit auf die Bildung einer Brucke werden analysiert. Ziel ist es, die Bildung und das Wachstum von Feststoffbrucken unter realen Lagerbedingungen zu beschreiben.

Zur Untersuchung der Ausbildung von Feststoffbrucken zwischen Harnstoffpartikeln werden die Veranderungen in der Kontaktregion zwischen zwei diskreten Partikeln gemessen. Die Untersuchungen werden anhand von Zweipartikelsystemen durchgefuhrt, die in einem Klimaschrank unter definierten Bedingungen gelagert werden. Hierbei wird der Einfluss der Parameter – mechanische Belastung der Partikel, Temperatur, relative Luftfeuchte und Lagerzeit – auf das Wachstum einer Feststoffbrucke zwischen den Partikeln analysiert. Ziel ist es, die geometrischen Veranderungen in der Kontaktregion zu beschreiben sowie die Zugfestigkeit der Feststoffbrucke zu messen.