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 f...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.展开更多
This paper presents the results of the application of a cold spray technique for structuring metallic surfaces with microparticles. The resulting changes in surface properties were characterized to observe their influ...This paper presents the results of the application of a cold spray technique for structuring metallic surfaces with microparticles. The resulting changes in surface properties were characterized to observe their influences on the tribological behavior of the structured surface. The spray technique was applied to a technical component, a 16MnCr5 steel chain pin, designed to be mounted in a linear reciprocating tribometer. TiO2 microparticles were used to structure the surface with a homogeneous distribution of singly dispersed particles, rather than a homogeneous closed coating on the surface. Tribometer tests were performed to directly compare structured and unstructured chain pins, and a significantly reduced sliding friction coefficient was observed for the structured pin. The pins were characterized in detail by surface analysis prior to and after application of the tribological load to set the surface parameters and surface chemistry, even on the microscale. It was confirmed that the particle structuring induced changes in the surface properties, and the durability of the changes after tribological loading was evaluated.展开更多
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 filter...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.展开更多
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 in...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.展开更多
文摘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.
基金financially supported by the German Research Foundation(DFG) Collaborative Research Center 926,Kaiserslautern,Germany "Microscale Morphology of Component Surfaces"
文摘This paper presents the results of the application of a cold spray technique for structuring metallic surfaces with microparticles. The resulting changes in surface properties were characterized to observe their influences on the tribological behavior of the structured surface. The spray technique was applied to a technical component, a 16MnCr5 steel chain pin, designed to be mounted in a linear reciprocating tribometer. TiO2 microparticles were used to structure the surface with a homogeneous distribution of singly dispersed particles, rather than a homogeneous closed coating on the surface. Tribometer tests were performed to directly compare structured and unstructured chain pins, and a significantly reduced sliding friction coefficient was observed for the structured pin. The pins were characterized in detail by surface analysis prior to and after application of the tribological load to set the surface parameters and surface chemistry, even on the microscale. It was confirmed that the particle structuring induced changes in the surface properties, and the durability of the changes after tribological loading was evaluated.
文摘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.
文摘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.
