The effect of turbulence on the mass transfer between a fluid and embedded small heavy inertial particles that experience surface reactions is studied. For simplicity, the surface reaction, which takes place when a gas phase reactant is converted to a gas phase product at the external surface of the particles, is unimolar and isothermal. Two effects are identified. The first effect is due to the relative velocity between the fluid and the particles, and a model for the relative velocity is presented. The second effect is due to the clustering of particles, where the mass transfer rate is inhibited due to the rapid depletion of the consumed species inside the dense particle clusters. This last effect is relevant for large Damköhler numbers, where the Damköhler number is defined as the ratio of the turbulent and chemical time scales, and it may totally control the mass transfer rate for Damköhler numbers larger than unity. A model that describes how this effect should be incorporated into existing simulation tools that utilize the Reynolds averaged Navier–Stokes approach is presented.

The effect of turbulence on the heterogeneous (solid-fluid) reactions of solid particles is studied numerically with Direct Numerical Simulations (DNS). A simplified reaction system is used, where the solid-fluid reaction is represented by a single isothermal reaction step. It is found that, due to the clustering of particles by the isotropic turbulence, the overall reaction rate is entirely controlled by the turbulence for large Damk\"ohler numbers. The particle clustering significantly slows down the reaction rate for increasing Damk\"ohler numbers which reaches an asymptotic limit that can be analytically derived. This implies that the effect of turbulence on heterogeneously reacting particles should be included in models that are used in CFD simulations of e.g. char burnout in combustors or gasifiers. Such a model, based on the chemical and turbulent time scales, is here proposed for the heterogeneous reaction rate in the presence of turbulence.Comment: Published online in the Proceedings of the Combustion Institut

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The effect of turbulence on heterogeneous reactions on the surface of char particles embedded in a turbulent oxidizer, consisting of oxygen and carbon-dioxide, is in this work studied numerically. It is shown that for small Damköhler numbers (Da), the char conversion rates are somewhat increased by the turbulence. This is found to be due to the increased mass transfer rate to the char particle surface that is caused by the turbulence-induced relative velocity between the char and the oxidizer. For large Damköhler numbers, however, the char conversion rate is strongly reduced due to particle clustering. This reduction is explained by the fact that when particles are clustered in densely populated particle clusters, the transfer of oxygen to the particles in the centre of the clusters is reduced since the oxygen is consumed by the particles closer to the external surface of the cluster. At the same time, high concentrations of oxygen exist in the voids between the particle clusters. This oxygen can not take part in the conversion of the char until it is transported to the char surface. The effects of turbulence on the heterogeneous reaction rates are furthermore modelled based on Direct Numerical Simulation (DNS) data for a simplified reacting gas particle system.

Imaging MS (MSI) has emerged as a valuable tool to study the spatial distribution of biomolecules in the brain. Herein, MALDI-MSI was used to determine the distribution of endogenous peptides in a rat model of Usher's disease. This rare disease is considered as a leading cause of deaf-blindness in humans worldwide. Cryosections of brain tissue were analyzed by MALDI-MSI to differentiate between healthy and diseased rats. MSI results were highly reproducible. Tissue-specific peptides were identified by MS/MS using LC-Orbitrap and MALDI-TOF/TOF analyses. These peptides were proposed for histological classification due to their particular spatial distribution in the brain, for example, substantia nigra, corpus callosum, and hippocampus. Several endogenous peptides showed significantly increased ion densities, particularly in the colliculi superiores and in the substantia nigra of diseased rats, including peptides derived from Fsd1, dystrobrevin-β, and ProSAAS. Furthermore, several proteolytic degradation products of the myelin basic protein were identified, of which one peptide is most likely mediated by calpain-2. Our findings contribute to the characterization of this animal model and include possible peptide markers of disease.