Flow-Optimization to Enhance Gas Quenching Efficiency for Helical Gears Specimen

Numerical simulations based on a conjugate heat transfer solver have been carried out to analyze various gas quenching configurations involving a helical gear streamed by an air flow at atmospheric pressure in a gas quenching chamber. In order to optimize the heat transfer coefficient distribution at key positions on the specimen, configurations involving layers of gears and flow ducts comprising single to multiple gears have been simulated and compared to standard batch configurations in gas quenching. Measurements have been performed covering the local heat transfer for single gears and batch of gears. The homogeneity of the heat transfer coefficient is improved when setting up a minimal distance between the gears (batch density) and when introducing flow ducts increasing the blocking grade around the gears. An offset between layers of the batch as well as flow channels around the gears plays a significant role in increasing the intensity and the homogeneity of the heat transfer in gas quenching process.

Particle penetration in fiber filters

Particle separation from gases is an important unit operation in manifold industrial applications,such as those conducted in environmental protection.For analysis of particle penetration and separation in fiber filters,standard dust particles (Al2O3)were loaded in the gas flow of a filter test facility and deposited within new and uncharged fiber filters.The loaded filters were analyzed by micro-computer tomography and scanning electron microscopy.Three-dimensional tomograms of the samples show an exponential decay of the penetration depth of the particles.This dependency is confirmed by simulations conducted using the discrete element method coupled with computational fluid dynamics within unloaded and loaded fiber structures.Microscale processes of particle separation at the fibers as well as the filtration efficiency and time-dependent filtering process are derived from the simuiations.Local particle clustering in the filter medium and partial filter clogging are thus identified.

Separating polydisperse particles using electrostatic precipitators with wire and spiked-wire discharge electrode design

Numerical simulations of electrostatic precipitators featuring wire and spiked electrode designs were performed to determine particle behavior and separation efficiency. The applied-voltage mechanism that alters the flow structure of particles through ionic winds and mean electric fields are revealed. Numeri- cal studies throughout the past years have shown these structures for channel and pipe configurations. However, less attention was given to field averaging for the ni,~r-product and electric field. Our study focuses on this averaging and illustrates relevant differences between multidimensional setups concern- ~ng these fields. Turbulence was modeled using the Reynolds-averaged Navier-Stokes equations with a second-order Reynolds-stress-model closure. A high three-dimensionality of the ionic wind-induced turbulence is presented. This leads to an increase in the submicron-particle precipitation rate. The results confirm the dependence of separation efficiency on particle density and permittivity, thereby showing the advantages of spiked wires compared with wire-plate setups used in electrostatic precipitators.

Dynamic flowsheet simulation of re-entrainment from particle layers formed inside electrostatic precipitators

Electrostatic precipitators clean away the particulate matter of exhaust gases in manifold industrial processes.Parameter studies of particle separation in the size range of several 100 nm to 25μm is of particular interest for the prediction of precipitation efficiencies and emissions.Models typically cover the transport of particles towards walls of the precipitator.However,no model yet covers the possible re-entrainment of particles from layers formed at the walls back into the gas flow.This study presents the implementation of a new time-resolving model for electrostatic precipitation utilizing a re-entrainment model.Experimental data support the results of modelling.The model uses a statistical approach based on properties of the particulate layer forming at the precipitator walls.The model is used for the analysis of the redispersion of particles in a laboratory-scale electrostatic precipitator(Sander,Gawor,&Fritsching,2018).Results show reduced precipitation efficiencies for particles larger than 5μm as particles have higher kinetic impact energies and lower bounding energy at the layer surface.Time dynamics reveal a steady-state behavior of the separation for CaCO3(limestone,trademark"Ulmer WeissR")while Al2O3(trademark"Pural NFR")precipitation is affected by layer buildup at the walls increasing over several minutes.

DROPLETS AND PARTICLES IN SPRAYS: TAILORING PARTICLE PROPERTIES WITHIN SPRAY PROCESSES

Particle generation via atomization and spray processes is a widely applied method for powder production. By means of atomization processes, the relevant particle properties may be tailored to the powder user's need in a wide range. Understanding and control of the main subprocesses of atomization is a key feature for choosing a suitable type of spray process and operation conditions. Tailoring particle properties and extending the applications of particle production beyond the current limits is also possible in this way. This contribution highlights some features of spray processes for powder production, namely the gas- and fluid-dynamic processes involved, the materials-related subprocesses, and the formation of the multiphase flow in the spray. As an example, the production of fibre- or sphere-shaped particles from melt atomization is discussed.