Multiscale simulation of fine grinding and dispersing processes: Stressing probability, stressing energy and resultant breakage rate

Quantification and modeling of macroparticle-induced mechanical stress for varying shake flask cultivation conditions

In biotechnological processes, filamentous microorganisms are known for their broad product spectrum and complex cellular morphology. Product formation and cellular morphology are often closely linked, requiring a well-defined level of mechanical stress to achieve high product concentrations. Macroparticles were added to shake flask cultures of the filamentous actinomycete Lentzea aerocolonigenes to find these optimal cultivation conditions. However, there is currently no model concept for the dependence of the strength and frequency of the bead-induced stress on the process parameters. Therefore, shake flask simulations were performed for combinations of bead size, bead concentration, bead density and shaking frequency. Contact analysis showed that the highest shear stresses were caused by bead-bottom contacts. Based on this, a newly generated characteristic parameter, the stress area ratio (SAR), was defined, which relates the bead wall shear and normal stresses to the total shear area. Comparison of the SAR with previous cultivation results revealed an optimum pattern for product concentration and mean product-to-biomass related yield coefficient. Thus, this model is a suitable tool for future optimization, comparison and scaling up of shear-sensitive microorganism cultivation. Finally, the simulation results were validated using high-speed recordings of the bead motion on the bottom of the shake flask.

Characterization of Stressing Conditions in a High Energy Ball Mill by Discrete Element Simulations

The synthesis of sulfide solid electrolytes in ball mills by mechanochemical routes not only is efficient but also can enable the upscaling of material synthesis as required for the commercialization of solid-state battery materials. On a laboratory scale, the Emax high energy ball mill accounts for high stresses and power densities, as well as for temperature control, to prevent damage to the material and equipment even for long process times. To overcome the merely phenomenological treatment, we characterized the milling process in an Emax by DEM simulations, using the sulfide solid electrolyte LPS as a model material for the calibration of input parameters to the DEM, and compared it to a planetary ball mill for a selected parameter set. We derived mechanistic model equations for the stressing conditions depending on the operation parameters of rotational speed, media size and filling ratio. The stressing conditions are of importance as they determine the outcome of the mechanochemical milling process, thus forming the basis for evaluating and interpreting experiments and for establishing scaling rules for the process transfer to larger mills.

Simulation of Grinding Media Motion and Collisions in Wet-Operated Accelerator-Mill Using DEM Coupled with CFD

The relative motion and collision between grinding media in a wet-stirred accelerator mill are modelled using the discrete element method (DEM) coupled with computational fluid dynamics (CFD). The local average normalized grinding media velocity profile is employed to divide the grinding chamber into four volumes, which facilitates the analysis of the stress energy distribution. The local grinding media filling levels, velocity distributions, stress energy distributions and energy efficiencies are compared at various total grinding media filling levels and stirrer speeds. The rationality of the division of stress energy volume was verified by the stress energy distribution. The stress intensity, stress number and collision stress energy from the grinding media’s motion and particle collisions exhibited different distributions, with the stress number playing a leading role in the collision stress energy distribution. Moreover, energy efficiency is quantitatively characterized under different process conditions. This simulation-based research provides a theoretical reference for the industrial application and product development of accelerator mills used for grinding applications.

Exploring space-energy matching via quantum-molecular mechanics modeling and breakage dynamics-energy dissipation via microhydrodynamic modeling to improve the screening efficiency of nanosuspension prepared by wet media milling

Introduction: The preparation of nanosuspensions by wet media milling is a promising technique that increases the bioavailability of insoluble drugs. The nanosuspension is thermodynamically unstable, where its stability might be influenced by the interaction energy between the stabilizers and the drugs after milling at a specific collision energy. However, it is difficult to screen the stabilizers and the parameters of milling accurately and quickly by using traditional analysis methods. Quantum-molecular mechanics and microhydrodynamic modeling can be applied to improve screening efficiency.Areas covered: Quantum-molecular mechanics model, which includes molecular docking, molecular dynamics simulations, and data on binding energy, provides insights into screening stabilizers based on their molecular behavior at the atomic level. The microhydrodynamic model explores the mechanical processes and energy dissipation in nanomilling, and even combines information on the mechanical modulus and an energy vector diagram for the milling parameters screening of drug crystals.Expert opinion: These modeling methods improve screening efficiency and support screening theories based on thermodynamics and physical dynamics. However, how to reasonably combine different modeling methods with their theoretical characteristics and further multidimensional and cross-scale simulations of nanosuspension formation remain challenges.

Grinding Media Motion and Collisions in Different Zones of Stirred Media Mills

Product fineness during grinding in stirred media mills is mainly influenced by the specific energy input, the stress energy transferred by the colliding grinding media and the stress frequency. The stress energy from grinding media collisions is heterogeneously distributed in stirred media mills. Herein, in order to characterize the stress energy distribution and the local grinding media collision frequencies, the grinding media motion was calculated using discrete element method (DEM) simulations coupled with computational fluid dynamics (CFD). The local grinding media concentration, velocity profiles, grinding media collisions and stress energies were compared for varied total grinding media fillings and stirrer speeds. It was confirmed that the normalized grinding media velocity profile can be used to divide the grinding chamber into four types of zones that allow the modeling of the stress energy distribution. However, the collision frequency showed very different distributions for varied stirrer velocities and grinding media fillings.

Mechanistic Modeling of Wet Stirred Media Milling for Production of Drug Nanosuspensions

Drug nanocrystals have been used for a wide range of drug delivery platforms in the pharmaceutical industry, especially for bioavailability enhancement of poorly water-soluble drugs. Wet stirred media milling (WSMM) is the most widely used process for producing dense, stable suspensions of drug nanoparticles, also referred to as nanosuspensions. Despite a plethora of review papers on the production and applications of drug nanosuspensions, modeling of WSMM has not been thoroughly covered in any review paper before. The aim of this review paper is to briefly expose the pharmaceutical scientists and engineers to various modeling approaches, mostly mechanistic, including computational fluid dynamics (CFD), discrete element method (DEM), population balance modeling (PBM), coupled methods, the stress intensity-number model (SI-SN model), and the microhydrodynamic (MHD) model with a main focus on the MHD model for studying the WSMM process. A total of 71 studies, 30 on drugs and 41 on other materials, were reviewed. Analysis of the pharmaceutics literature reveals that WSMM modeling is largely based on empirical, statistically based modeling approaches, and mechanistic modeling could help pharmaceutical engineers develop a fundamental process understanding. After a review of the salient features and various pros-cons of each modeling approach, recent advances in microhydrodynamic modeling and process insights gained therefrom were highlighted. The SI-SN and MHD models were analyzed and critiqued objectively. Finally, the review points out potential research directions such as more mechanistic and accurate CFD-DEM-PBM simulations and the coupling of the MHD-PBM models with the CFD.

Breakage Characterization of Magnetite under Impact Loads and Cyclic Impact Loading

A series of impact compression tests were conducted to study the breakage characteristics of magnetite, as well as the impact pressure on its strain rate and dynamic compressive strength. The dynamic mechanical properties and fragmentation size distribution of magnetite under diverse impact loads and cyclic impact were investigated, with fractal theory as a basis and split Hopkinson pressure bar (SHPB). Breakage methods were also employed to analyze the fracture morphology of magnetite. According to the result, the fractal dimension can reflect the distribution of fragments in various sizes. If the strain rate increases, the fractal dimension will be larger, the fragment size will be finer, and the fragmentation degree will be more influential. A micro-analysis of SEM images demonstrates that the fracture morphology is determined by mineral properties. Under low load cyclic impact, intergranular fracture is the main fractography. Besides, the intergranular fracture will be changed to a transgranular one as the impact load increases.

Possibilities and Limits of Computational Fluid Dynamics-Discrete Element Method Simulations in Process Engineering: A Review of Recent Advancements and Future Trends

Fluid-solid systems play a major role in a wide variety of industries, from pharmaceutical and consumer goods to chemical plants and energy generation. Along with this variety of fields comes a diversity in apparatuses and applications, most prominently fluidized and spouted beds, granulators and mixers, pneumatic conveying, drying, agglomeration, coating, and combustion. The most promising approach for modeling the flow in these systems is the CFD-DEM method, coupling computational fluid dynamics (CFD) for the fluid phase and the discrete element method (DEM) for the particles. This article reviews the progress in modeling particle-fluid flows with the CFD-DEM method. A brief overview of the basic method as well as methodical extensions of it are given. Recent applications of this simulation approach to separation and classification units, fluidized beds for both particle formation and energy conversion, comminution units, filtration, and bioreactors are reviewed. Future trends are identified and discussed regarding their viability.

Cryo-milling using a spherical sugar: Contamination-free media milling technology

Milling beads experience wear upon repeated use. And milling beads made of material that is safe when ingested have not yet been developed. The present report describes the development and characteristics of spherical d-mannitol (SDM) beads, which would be safe when ingested. The model drug phenytoin was dispersed in liquid nitrogen along with SDM and the materials were agitated at high speed. The effects of the amount of beads, agitation speed, and milling time on phenytoin particle size, yield, and bead fractures were investigated using a central composite experimental design. The diameter of milled phenytoin particles decreased significantly as the amount of SDM beads and agitation speed increased. In contrast, no difference was found in the diameter with milling time. Although the fractured SDM ratio increased slightly at higher agitation speeds, the SDM was not broken and was durable enough for milling. This milling technique was applicable not only to phenytoin but also to other drug substances. Bead durability and applicability indicated that SDM can be used as wet milling beads that are considered safe for use if ingested.