采用Fe_(2)O_(3)/水纳米流体强化翅片管壳换热器的传热

为了优化效率和减少能量损失,需要对传热机理及热性能进行全面研究。在基液中加入不同的纳米颗粒可提高热交换器的热性能。设计了一种翅片管壳式换热器,以体积浓度分别为1%、1.5%、2%的Fe_(2)O_(3)/水纳米流体作为换热流体,研究不同体积浓度的纳米流体对传热的影响,并将所得结果与纯水作为换热流体结果进行比较。采用ANSYS Fluent软件对传热过程进行数值模拟。数值模拟结果表明:纳米流体可成功应用于换热器中,提高Fe_(2)O_(3)纳米颗粒的体积分数可以获得更大的热能,而不会产生明显的压降。此外,当纳米流体中Fe_(2)O_(3)的体积分数为2%时,其传热速率提高率最高,为19.1%。

Influences of Pr and Ta doping concentration on the characteristic features of FTO thin film deposited by spray pyrolysis

The Pr and Ta separately doped FTO（10 at.% F incorporated Sn O2） films are fabricated via spray pyrolysis. The microstructural, topographic, optical, and electrical features of fluorine-doped TO（FTO） films are investigated as functions of Pr and Ta dopant concentrations. The x-ray diffraction（XRD） measurements reveal that all deposited films show polycrystalline tin oxide crystal property. FTO film has（200） preferential orientation, but this orientation changes to（211） direction with Pr and Ta doping ratio increasing. Atomic force microscopy（AFM） and scanning electron microscopy（SEM） analyses show that all films have uniform and homogenous nanoparticle distributions. Furthermore, morphologies of the films depend on the ratio between Pr and Ta dopants. From ultraviolet-visible（UV-Vis） spectrophotometer measurements, it is shown that the transmittance value of FTO film decreases with Pr and Ta doping elements increasing. The band gap value of FTO film increases only at 1 at.% Ta doping level, it drops off with Pr and Ta doping ratio increasing at other doped FTO films. The electrical measurements indicate that the sheet resistance value of FTO film initially decreases with Pr and Ta doping ratio decreasing and then it increases with Pr and Ta doping ratio increasing. The highest value of figure of merit is obtained for 1 at.% Ta- and Pr-doped FTO film. These results suggest that Pr- and Ta-doped FTO films may be appealing candidates for TCO applications.

Persisting challenges for performance-based building assessment

Intense research and refinement of the tools used in performance-based seismic engineering have been made,but the maturity and accuracy of these methods have not been adequately confirmed with actual data from the field. The gap between the assumed characteristics of actual building systems and their idealized counterparts used for analysis is wide. When the randomly distributed flaws in buildings as they exist in urban areas and the extreme variability of ground motion patterns combine,the conventional procedures used for pushover or dynamic response history analyses seem to fall short of reconciling the differences between calculated and observed damage. For emergency planning and loss modeling purposes,such discrepancies are factors that must be borne in mind. Two relevant examples are provided herein. These examples demonstrate that consensus-based analytical guidelines also require well-idealized building models that do not lend themselves to reasonably manageable representations from field data. As a corollary,loss modeling techniques,e.g.,used for insurance purposes,must undergo further development and improvement.

不同参数对热泵性能影响的实验研究

在热泵领域,有许多影响装置性能和效率的参数。本研究采用实验方法研究重要参数对热泵性能的影响。在不同工况下,利用实验室热泵装置研究制冷剂类型和充注量、压缩机油黏度、压缩机冷却风扇、二次流体温度和流量等参数的影响。选择不同的制冷剂作为热泵的循环流体。本文在研究不同参数对COP的影响之外,还对其经济性进行了分析。结果表明,制冷剂充注量是影响COP的主要参数之一,添加合适的制冷剂可使系统性能提高11%以上。此外,通过选择低黏度压缩机油,系统性能提高18%。当采用冷却风扇冷却压缩机元件时,系统性能提高超过6%。

A Pt/MnV_(2)O_(6) nanocomposite for the borohydride oxidation reaction

Problems associated with carbon support corrosion under operating fuel cell conditions require the identification of alternative supports for platinum-based nanosized electrocatalysts.Platinum supported on manganese vanadate(Pt/MnV_(2)O_(6))was prepared by microwave irradiation method and characterized using X-ray diffraction,Fourier-transform infrared spectroscopy,X-ray photoelectron spectroscopy,scanning electron microscopy with energy dispersive spectroscopy,and transmission electron microscopy.The borohydride oxidation reaction(BOR)on Pt/MnV_(2)O_(6) was studied in highly alkaline media using voltammetry,chronoamperometry,and electrochemical impedance spectroscopy.BOR electrocatalytic activity of Pt/MnV_(2)O_(6) was also compared with that of commercial Pt/C(46 wt%Pt)electrocatalyst.The apparent activation energy of BOR at Pt/MnV_(2)O_(6) was estimated to be 32 k J mol^(-1) and the order of reaction to be 0.51,indicating that borohydride hydrolysis proceeds in parallel with its oxidation.Long-term stability of Pt/MnV_(2)O_(6) under BOR typical conditions was observed.A laboratory-scale direct borohydride fuel cell assembled with a Pt/MnV_(2)O_(6) anode reached a specific power of 274 W g^(-1).Experimental results on Pt/MnV_(2)O_(6) were complemented by DFT calculations,which indicated good adherence of Pt to MnV_(2)O_(6),beneficial for electrocatalyst stability.

Three new records of Cortinarius(Cortinariaceae)for the Turkish Mycota from Trabzon,Turkey

Basidiomata of Cortinarius were collected during the field studies in 2019 and identified based on both morphological and molecular data.Three Cortinarius species viz.Cortinarius cadi-aguirrei,C.cinnamoviolaceus and C.variegatus are recorded for the first time from Turkey.Full descriptions,color figures,a simple phylogenetic tree and a short discussion are provided here.

A Comparative Study of Fabrication of Long Wavelength Diode Lasers Using CCl2F2/O2 and H2/CH4

We report comparatively on fabrication of two-section ridge-waveguide tapered 3 quantum well (QW) InGaAsP/InP (1300 nm) and 5 QW AlGaInAs/InP (1550 nm) diode lasers. Gas mixtures of CCl2F2/O2 and H2/CH4 were used to form ridge-waveguide on the lasers with InP-based material structures. As known, chlorine- and hydro-carbon based gases are used to fabricate ridge-waveguide structures. Here, we show the difference between the structures obtained by using the both gas mixtures in which surface and sidewall structures as well as performance of the lasers were analysed using scanning electron microscopy. It is demonstrated that gas mixtures of CCl2F2/O2 highly deteriorated the etched structures although different flow rates, rf powers and base pressures were tried. We also show that the structures etched with H2/CH4 gas mixtures produced much better results that led to the successful fabrication of two-section devices with ridge-waveguide. The lasers fabricated using H2/CH4 were characterized using output power-current (P-I) and spectral results.

Promoting Pedestrian Transportation for Reducing Air Pollution from Urban Transport

Increasing air pollution around the world causes many problems,especially in the field of health.Air pollution affects not only human health but also other living things health.The factors that cause air pollution the most are heating,industry,and transportation.Many countries in the world carry out various studies to reduce the effect of these factors on air pollution.Especially in the field of transportation,studies have been quite a lot in recent years.In this study,air pollution caused by transportation in Erzurum,Turkey has investigated.Emission amounts of NO_(X),PM_(10),and SO_(2) values have calculated according to the types of vehicles in the city.Then,the amount of emissions from transportation in the total sector has revealed.The transportation structure of the city has examined in general terms and the missing aspects in terms of pedestrian transportation have revealed.Finally,some solution proposals aiming to encourage the use of pedestrian transportation and micro mobility vehicles in order to reduce motor land vehicles are presented.

Wear Resistance and Non-Magnetic Layer Formation on 316L Implant Material with Plasma Nitriding

In this study, the applicability of plasma nitriding treatment in the production of non-magnetic and corrosion resistant layer on 316L stainless steel implant material was investigated. 316L stainless steel substrates were plasma nitrided at temperatures of 350 ℃, 375 ℃, 400 ℃, 425 ℃ and 450 ℃ for 2 h in a gas mixture of 50% N2-50% H2, respectively. It was determined that the treatment temperature is the most important factor on the properties of the corrosion resistant layer of 316L stainless steel. The results show that s-phase formed at the temperatures under 400 ℃, and at the temperatures above 400 ℃, instead of s-phase, CrN and y＇-Fe4N phases were observed in the modified layer. The electrical resistivity and surface roughness of the modified layer increase with treatment temperature. Under 400 ℃ the corrosion resistance increased with the temperature, above 400 ℃ it decreased with the increase in treatment temperature. It was analyzed that the electrical resistivity and the soft （ideal） ferro- magnetic properties of 316L stainless steel increased with treatment temperature during nitriding treatment. Also, plasma ni- triding at low temperatures provided magnetic behavior close to the ideal untreated 316L stainless steel.

Wear Behavior of Plasma Oxidized CoCrMo Alloy under Dry and Simulated Body Fluid Conditions

In this study, CoCrMo alloy was oxidized in plasma environment at the temperatures of 600 ℃ to 800 ℃ for 1 h to 5 h with 100% 02 gas and its tribological behavior was investigated. After the plasma oxidizing process, the compound and diffusion layers were formed on the surface. XRD results show that Cr203, a-Co and ε-Co phases diffracted from the modified layers after plasma oxidizing. The untreated and treated CoCrMo samples were subjected to wear tests both in dry and simulated body fluid conditions, and normal loads of 2 N and 10 N were used. For the sliding wear test, alumina balls were used as counter materials. It was observed that the wear resistance of CoCrMo alloy was increased after the plasma oxidizing process. The lowest wear rate was obtained from the samples that were oxidized at 800 ℃ for 5 h. It was detected that both wear environment and load have significant effects on the wear behavior of this alloy, and the wear resistance of oxidized CoCrMo alloy is higher when oxide-based counterface is used. The wear rates of both untreated and plasma oxidized samples increase under high loads.

Corrosion Behavior ofAg-doped TiO2 Coatings on Commercially Pure Tita- nium in Simulated Body Fluid Solution

TiO2 films including different amounts of Ag obtained by sol-gel method on commercially pure titanium （CP-Ti） and the corrosion properties of Ag-doped TiO2 films were investigated by potentiodynamic polarisation and Electrochemical ImpedanceSpectroscopy （EIS） tests in Simulated Body Fluid （SBF） solution. The results were compared with untreated and un-doped samples. Surface characterizations before and after the corrosion tests were performed by the Scanning Electron Microscopy （SEM） and X-ray Diffraction （XRD） analysis. It was observed that Ag-doping for TiO2 films improved the corrosion resistance when compared with untreated and un-doped TiO2 film coated samples. The highest corrosion resistance was obtained from Ag-doped samples coated with a solution of 0.05 M Ag.

Experimental Analysis and Evaluation of Thermostat Effects on Engine Cooling System

Thermostat as a part of engine cooling system has a significant role in the shortening warm-up time and regulating the engine in proper temperature to approach optimal performance.Whereas,there is not adequate research on this part of the cooling system and its responsibility.Considering this gap and also being used in large scale,this study is intended to evaluate performance and reflex of the wax type thermostat in different engine working conditions.In this regard,performance of engine cooling system was investigated in various engine speeds and loads to reveal positive and negative influences of thermostat on engine cooling efficiency and engine performance.According to observed results,warm-up period and fuel consumption decrease by using a thermostat.On the other hand,however,the temperature oscillation of coolant fluid passing through engine increases sharply,which causes a disruption in the regulating engine temperature and also a possibility of the fluid boiling rises in some regions of the engine that increases the risk of damage in the engine parts.Engine temperature,fuel consumption,warm-up duration and emissions were provided and compared in two operation modes,with and without thermostat.

Corrosion Properties of Ceramic-Based TiO_(2)Films on Plasma Oxidized Ti6Al4V/316L Layered Implant Structured Manufactured by Selective Laser Melting

Selective Laser Melting(SLM),one of the metal additive manufacturing methods in the powder bed,is frequently used in the production of 316L stainless steel biomaterial.In this study,the effect of duplex surface modification(metal additive manufacturing and plasma oxidizing)on the corrosion resistance of 316L was investigated.Ti6Al4V layer was formed by additive manufacturing on 316L produced by selective laser melting method.The obtained layered Ti6Al4V/316L samples were oxidized by plasma at 650℃–750℃ and 1 h–4 h parameter conditions.TiO_(2)ceramic layer was formed on the Ti6Al4V/316L structure by plasma oxidation process in several layer thicknesses.Corrosion properties of the TiO_(2)layer were determined by Open Circuit Potential(OCP),potentiodynamic polarization,and Electrochemical Impedance Spectroscopy(EIS)tests in Simulated Body Fluid(SBF)solution.Also,the surface characterizations of the samples were determined by the Vickers micro-hardness tester,Scanning Electron Microscopy(SEM),and X-Ray Diffractometer(XRD)analysis.From the results,it was obtained that the corrosion resistance of the plasma oxidized was higher than the untreated 316L and layered Ti6Al4V/316L samples.The best corrosion resistance was obtained under the 750℃ and 4 h parameter conditions because of the increasing plasma oxidizing time and temperature.

The Effects of Aging Time on the Structural and Electrochemical Properties of Composite Coatings on CP-Ti Substrate

TiO2-SiO2 composite films were produced on commercially pure titanium （CP-Ti） substrate by a sol-gel method to in- vestigate the behavior of sol aging time and its potential effects on the structural and electrochemical properties of composite coatings. Anatase-TiO2 and quartz-SiO2 peaks were observed on all composite coated samples according to XRD results. It was observed that the average grain size increased with sol aging time. Also, the average smallest grain size was seen at composite coatings prepared from unaged sol according to the width of the peaks. Electrochemical behavior of coated samples was mainly investigated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy （EIS） in Simulated Body Fluid （SBF） solution. In corrosion tests, the composite coatings showed better anti-corrosion behavior than that of uncoated samples. In addition, the corrosion properties of the composite films were considerably affected by sol aging time. Corrosion resistance of coatings decreased with increasing aging time and the best result was obtained from composite coatings prepared from unaged sol.

与流固耦合相关的溃坝问题中阻尼的数值及实验研究（英文）

目的:1.通过全面的实验研究考察阻尼在流固耦合(FSI)问题中的影响作用;2.提出一套光滑粒子流体动力学(SPH)和有限元方法(FEM)相结合的耦合算法,并对流固耦合系统进行数值模拟。创新点:1.通过一系列实验研究惯性驱动问题中阻尼的影响并使用本文提出的数值方法进行验证;2.该数值方法能够在不解耦的情况下对完整系统进行求解。方法:1.构建数值模型模拟流体和弹性结构之间的强烈相互作用;2.利用SPH和FEM对流体和结构分别进行模型化;3.采用接触力学对系统中的流固耦合机理进行建模。结论:1.基于SPH-FEM耦合的FSI模型可成功模拟自由液面形状、橡胶板的位移以及容器壁上的压强;2.模拟结果显示,在连续相互作用的惯性驱动问题中阻尼并不是必要的考虑因素。