IMPELLER CLEARANCE EFFECT ON OFF BOTTOM PARTICLE SUSPENSION IN AGITATED VESSELS

The effect of impeller off bottom clearance on the power input requirement for off bottom solid suspension was examined for 45° pitched blade impellers in flat and round bottom fully baffled agitated vessels. Results showed a similar dependence as obtained for radial flow impellers when similar flow patterns were observed. The dependence appears to be independent of the impeller diameter to tank diameter ratio and vessel shape.     

Production of microparticles from milk fat products using the Supercritical Melt Micronization (ScMM) process

The ScMM (Supercritical Melt Micronization) process was applied for the production of microparticles from anhydrous milk fat (AMF) and a diacylglycerol-based modified milk fat (D-AMF). Both fats were able to dissolve ca. 30 wt% CO₂ in the studied pressure and temperature ranges, being the CO₂ amount slightly higher for AMF. A melting point depression was observed in both systems in the presence of CO₂. Two powder morphologies were obtained (spherical hollow particles and a mass sponge-like broken particles) depending on the ScMM process conditions. The concentration of CO₂ in the fat melt was the main process variable affecting the particle morphology, followed by the temperature of the melt. The small broken particles originated from the breakage of spherical fat particles that solidified before all CO₂ could escape from the atomized droplets. While the hollow spheres had a tendency to agglomerate, the broken microparticles constituted a free-flowing powder as long as they were stored at low temperatures (up to −18 °C). Both types of particles have a potential for being incorporated in refrigerated or frozen food products as a structuring agent.     

Discrete element analysis of experiments on mixing and stoking of monodisperse spheres on a grate

Understanding the details of the mixing and stoking process on grate firing systems is crucial for the optimization of the combustion process in waste or biomass incineration plants. The Discrete Element Method (DEM) can help to obtain further information on the mixing process within a bed of fuel particles. Especially the influence of a change in operational parameters can be examined avoiding large experimental effort. In the current paper five simulations for a generic grate are compared with the corresponding experiments. The experiments were carried out throughout an anterior parameter study on mixing and stoking on a grate [Sudbrock F.; Simsek E.; Wirtz S.; Scherer V.: “An experimental analysis of the influence of operational parameters on mixing and stoking of a monodisperse granulate on a grate”, Powder Technology 198, Issue 1, 29-37, 2010] [19]. The system considered is equipped with vertically moving bars which induce stoking. In a first approach monodisperse plastic spheres are used. The grate is encased by a transparent polycarbonate housing which provides optical access to the movement of the particles in the wall planes. The mixing process is measured and quantified by image analysis of the front wall of the grate. The mixing behaviour of the particle assembly observed in experiments and simulation appears to be very similar indicating that DEM is able to predict the particle mixing in the bed. In order to quantify the visual observations the mixing behaviour has been evaluated by different mixing parameters. They are compared in dependence of the number of strokes of the grate bars. A good agreement between measurements and simulations could be observed.     

常减压蒸馏装置腐蚀及防护

原油中含有大量盐、含硫化合物及酸性物质,对常减压整流装置及泵等设备产生了腐蚀破坏,严重影响着原油炼制工业的正常生产。本文对常减压蒸馏装置的腐蚀情况进行了综述,分析了产生腐蚀的主要原因,及针对各种现象所做的一系列工艺防护,设备防护以及安装先进的检测设备,从而提高炼油厂的运行周期和经济效益。     

Oxygen vacancy levels on gadolinia-doped ceria interlayer deposited by atmospheric pressure plasma jet for solid oxide fuel cells

The oxygen vacancy levels as a factor on different gadolinia-doped ceria interlayer (GDCi) films deposited on yttria stabilized zirconia (YSZ) electrolyte substrates by an atmospheric pressure plasma jet (APPJ) via precursor solution of nitrate salts are investigated. Focusing on the effect of carrier gases, scanning electron microscopy (SEM), Raman, and X-ray diffraction (XRD) are implemented for the materials characterization of the as-deposited GDCi films and sintered-GDCi films at various temperatures. The higher level of oxygen vacancies in GDCi films adhered on 8YSZ electrolyte are evidently analyzed using Ar as the carrier gas during the deposition, of which the interdiffusion resulted in the formation of (GDC + YSZ) solid solution for sintering over 1300?°C degraded the total conductivity. The deposition of GDCi films on 8YSZ by APPJ method using O₂ carrier gas significantly improved the total conductivities of the whole electrolyte layers. Moreover, this study provides the useful insight into the oxygen vacancy levels on GDC films as interlayer (GDCi) to improve the values of open circuit voltage in LSM/GDCi/YSZ/Pt full-cell, as well as offering the efficiency of APPJ as one step deposition process.     

Ozone Production in a Dielectric Barrier Discharge with Ultrasonic Irradiation

Ozone production has been investigated using an atmospheric pressure dielectric barrier discharge in pure O₂ at room temperature with and without ultrasonic irradiation. It was driven at a frequency of either 15 kHz or ～40 kHz. The ozone production was highly dependent on the O₂ flow rate and the discharge power. Furthermore, powerful ultrasonic irradiation at a fundamental frequency of ～30 kHz with the sound pressure level of ～150 dB into the discharge can improve the ozone production efficiency, particularly when operated at the frequency of 15 kHz at the flow rate of 15 L/min.     

Deactivation of Pt/wire-mesh and vanadia/monolith catalysts applied in selective catalytic reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> in flue gas

In this study the deactivation of Pt/wire mesh and vanadia/monolith catalysts by aerosol particles of some inorganic salts (K₂SO₄, KCl and ZnCl₂) with high or low melting points has been investigated. The aerosol particles may either diffuse within the matrix of the catalysts and block the mezzo and micro pores, or deposit on the outer surface of the catalysts and form a porous layer causing a mass transfer resistance that ultimately deactivates the catalysts. It has been observed that in both Pt/wire mesh and vanadia/monolith catalysts the deactivation effect of ZnCl₂ was more pronouced compared to other salts. As an example, after 31 hours of exposure to ZnCl₂, 10% of the catalysts activities was lost. This may be related to the ZnCl₂ lower melting point in comparison with other poisons. These results are in agreement with the previous findings for deactivation of wire-mesh catalysts used for oxidation of volatile organic compounds (VOC) and CO by exposing the catalysts to the aerosols generated from inorganic salts.     

Preparation and characterization of alumina submicron fibers by plasma assisted calcination

Ceramic alumina nanofibers were prepared by plasma-assisted calcination (PAC) using atmospheric pressure plasma. Electrospun polyvinyl pyrrolidone/aluminium butoxide fibers were pre-treated by plasma generated in ambient air using a special type of coplanar dielectric barrier discharge. The effect of plasma on fibers and structural, chemical and crystalline properties of obtained ceramic nanofibers were characterized using X-Ray Photoelectron Spectroscopy and Scanning Electron Microscopy, Energy-dispersive X-ray Spectroscopy and X-Ray Diffraction. Thermogravimetric and differential thermal analysis were used for the study of thermal behaviour of untreated and plasma-treated samples. The ceramic fibers prepared by PAC exhibit suitable chemical composition, higher porosity, high length of fibers and better crystalline properties with simultaneous simplifying of the sintering process. The plasma pre-treatment of fibers results in a shortening of following thermal treatment, decrease of the required temperature and excludes a slow temperature increase as prevention of fibrous structure degradation typical in preparation of ceramic fibers by polymer-template techniques.     

Evolution mechanism of the microstructure and mechanical properties of plasma-sprayed yttria-stabilized hafnia thermal barrier coating at 1400 °C

Yttria stabilized hafnia (Hf_0.84Y_0.16O_1.92, YSH16) coatings were sprayed by atmospheric plasma spraying (APS). The effects of thermal aging at 1400 °C on the microstructures, mechanical properties and thermal conductivity of the coatings were studied. The results show that the as-sprayed coating was composed of the cubic phase, and the nano-sized monoclinic (M) phase was precipitated in the annealed coating. The presence of M phase effectively constrained the sintering of the coating due to its superior sintering-resistance. The Young's modulus kept at a nearly same level of ~78 GPa even after annealing, and the coating annealed for 6 h yielded a maximum value of hardness but revealed a declining tendency in the Vicker's hardness with prolonged sintering time. The thermal conductivity increased from 0.8-0.95 W m^-1 K^-1 at as-sprayed state to 1.6 W m^-1 K^-1 after annealing at 1400 °C for 96 h. The dual-phase coating is promising to serve at temperatures above 1400 °C due to its excellent thermal stability and mechanical properties.     

Present status and future prospects of plasma sprayed multilayered thermal barrier coating systems

Thermal barrier coatings (TBCs) play a pivotal role in protecting the hot structures of modern turbine engines in aerospace as well as utility applications. To meet the increasing efficiency of gas turbine technology, worldwide research is focused on designing new architecture of TBCs. These TBCs are mainly fabricated by atmospheric plasma spraying (APS) as it is more economical over the electron beam physical vapor deposition (EB-PVD) technology. Notably, bi-layered, multi-layered and functionally graded TBC structures are recognized as favorable designs to obtain adequate coating performance and durability. In this regard, an attempt has been made in this article to highlight the structure, characteristics, limitations and future prospects of bi-layered, multi-layered and functionally graded TBC systems fabricated using plasma spraying and its allied techniques like suspension plasma spray (SPS), solution precursor plasma spray (SPPS) and plasma spray –physical vapor deposition (PS-PVD).