Comprehensive Investigation of wet Powder Blending

Flow of highly saturated wet granular matter is encountered in a wide range of engineering applications, including chemical, pharmaceutical, and mechanical engineering, food processing and petroleum engineering. However, the detailed understanding, modeling and simulation of the effects stemming from the liquid bridges in these materials still pose significant challenges. The objective of the proposed work is the development of a new method to investigate wet granular flows in great detail. Specifically, we plan to (i) develop a numerical strategy to directly simulate wet agglomerates, even at high liquid saturation levels, (ii) build up an innovative experimental setup to validate our simulations, (iii) apply the developed methodology to relevant systems, and (iv) couple the results of our direct simulations with a relatively new method, i.e., the Discrete Element Method (DEM). In the first part of the proposed work we will adapt a state-of-the-art numerical strategy initially developed for gas- liquid multiphase flow. Our work will include the modeling of the solid-phase geometry, the accurate treatment of the dynamic contact angle and wetting dynamics, a detailed contact detection between solid particles and finally the modeling of the forces between particles in contact. With this adapted numerical method we will be able - for the first time - to simulate the flow of a liquid and a gaseous phase in moving complex granular matter. This will, for example, enable us to look at the details of the liquid distribution in sheared granular matter, which is essential for, e.g., granulation processes. In the second part we will construct an innovative experimental setup to investigate static as well as dynamic forces in a particle bed. Exact control of the relative distance and motion between the particles will be achieved using ultra-precise micromanipulators. The novelty of this setup is that we will be able to measure the forces between multiple particles, up to high saturation levels and under defined relative velocity. Also, we will use a shear cell to validate our simulation results for a large bed of particles. Furthermore, we will apply our method to study topics associated with wet granular matter, including the microscale simulation of granules, consolidation and liquefaction effects, mixing problems associated with wet granular matter, as well as the dissolution of tablets. Finally, we will connect our knowledge obtained from the detailed simulations with other simulation tools already in use by academia and industry. Specifically, it is our goal to develop models for the Discrete Element Method that predict the distribution of liquid bridges, as well as dynamic and static forces at high saturation levels. The results of the proposed work are expected to have significant impact on the use of simulations in many branches of science, like pharmaceutical engineering, geomechanics or petroleum engineering. Furthermore, significant fundamental knowledge will be gained during the application of the methodology in the area of granulation and drying, as well as tablet dissolution. This will be an important factor for the rational (opposed to the currently applied trial-and-error based) development of new drug delivery systems.

The description of flow and mixing behaviour of wet granular matter poses a number of challenges, mainly connected to the unknown distribution of liquid in its pores. In these systems, the local liquid concentration is often described by the amount of liquid in bridges connecting individual particles. Hence, the key challenges are (i) to predict the transport rate of liquid into these bridges, as well as (ii) their transport rate due to moving particles. Within the current project we focused on the dynamic modeling of liquid bridge volumina, having applications in the food & pharma, as well as the petrochemical industry in mind. Specifically, we employed (i) numerical simulation models, as well as (ii) selected small-scale experiments to establish quantitative understanding of the liquid bridge formation rate. In the first part of the proposed work we adapted a state-of-the-art numerical strategy, which was initially developed for gas-liquid flow, e.g., bubbles rising in water. Our work included the modeling of the solid-phase geometry, the accurate treatment of the dynamic contact angle and wetting dynamics, as well as liquid and gas flow around the particles. This enabled us, for example, to study the genesis of individual liquid bridges, and to look at the very details of the liquid distribution in granular matter. Consequently, we derived models for predicting the temporal change of the liquid bridge volume. In the second part we constructed innovative experimental setups to investigate gravity-driven granular flow, as well vibro-fluidized particle beds. These experiments were helpful to validate our predictions. In the third part we combined our knowledge obtained from the detailed simulations (performed in part one) with other simulation tools already in use by academia and industry. Specifically, we implemented our newly-derived models into the Discrete Element Method (DEM) to predict the distribution of liquid bridges, as well as dynamic and static forces at high saturation levels in flowing granular matter. Then, we applied our advanced DEM to study flow and mixing in wet granular matter, including wet granulation in fluidized beds, as well as mixing in simple shear flow. The results of our work are expected to have significant impact on the use of simulations in many branches of science, like pharmaceutical engineering, geomechanics or petroleum engineering. The project established open-source simulation models and tools, which are now available to a broad audience for their future exploitation.