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Influence of cobalt on performance of Cu–CeO2 catalysts for preferential oxidation of CO
No full textCopper and cobalt oxides supported on CeO2 were investigated for preferential oxidation of carbon monoxide (CO-PROX) in the presence of excess hydrogen and CO2. (CuO)1−x(Co3O4)x/3−(CeO2)2.5 (x = 0, 0.25, 0.50, 0.75, 0.85 and 1) catalysts were prepared by coprecipitation method. These mixed oxide catalysts were characterized by several physicochemical techniques, such as BET surface area (SBET), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). XRD studies show the peaks related to CuO and Co3O4 phases in copper and cobalt containing CeO2 catalysts. The average particle size of the CeO2 crystallites is in the range of 8–10 nm as evaluated from HRTEM studies. XPS studies demonstrate that Cu, Co and Ce in (CuO)1−x(Co3O4)x/3−(CeO2)2.5 catalysts are presented in +2 and +1, +3 and +2 and +4 and +3 oxidation states, respectively. The catalyst with x = 0.75 shows better activity and selectivity towards CO-PROX. Though the catalyst with only copper (CuO–CeO2, x = 0) shows good activity but reverse water gas shift (RWGS) reaction is noticed at high temperature. On the other hand, RWGS reaction is suppressed on the cobalt containing CuO–CeO2 catalyst. Cobalt on CeO2 with x = 1 shows hardly any activity for PROX reaction at low temperatures. No methanation activity is observed on CuO–CeO2 or Co3O4–CeO2 catalysts. In contrast, combination of copper and cobalt on CeO2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content
Optimal Design Methodology for Planar Multi-Layered Radomes for Multiband Applications Using Nature Inspired Algorithm
No full textAn efficient nature inspired algorithm based on particle swarm optimization (PSO) is presented in this paper for the optimal design of planar multi-layered radomes for multiband applications. Material layer sequence and thickness profile are the two critical factors determining the position of passbands in the frequency range of operation as well as the transmission performance in those bands. These design aspects have to be appropriately optimized to achieve the desired
performance, and it becomes a daunting task for radome designers when a comparatively large database
of suitable materials is available in the solution space. Even though commercially available software
packages provide options (like particle swarm optimization (PSO), genetic algorithm (GA), etc.) for the
optimization of thickness profile, they do not have the functionality for optimizing the position of a
specific material inside the multi-layered radome wall configuration. In this regard, the proposed PSObased algorithm automatically chooses suitable materials from the predefined database and optimizes
the thickness for each layer, in order to achieve superior transmission in user defined passbands.
Furthermore, the superiority of the indigenously developed algorithm over the optimization techniques
available in full wave simulation software (FEKO) w.r.t. accuracy and computational efficiency is also
established using suitable case studies and validations. Although PSO has been used in the context
of radomes, its application for the simultaneous optimization of material layer sequence and thickness
profile of multi-layered radomes is not reported in literature to the best of our knowledge
Influence of crack driving force on correlating stress ratio effects in fatigue crack growth rate of a nickel base super alloy IN720
No full textDamage tolerance evaluation under service loads requires a unified constant amplitude fatigue crack growth law for the material with nullified stress ratio effects. Several types of crack driving force parameters have been proposed in the past to correlate stress ratio effects on fatigue crack growth rates in various materials. In the present investigation, an effort was made to use four different crack driving force parameters to eliminate stress ratio effects in a nickel base super alloy IN720. Constant amplitude fatigue crack growth rate of Inconel 720 (IN720) was experimentally determined at various stress ratios, R ranging from R = 0.1 to 0.7. All the tests were performed at room temperature and in laboratory air condition in a 100-KN servo-hydraulic test machine using compact tension specimen and following ASTM test standard procedures. As expected, increasing the stress ratio increased crack growth rates and decreased threshold stress intensity factor range, ΔKth. The conventional crack growth rate, da/dN versus stress intensity factor range, ΔK data was modified and re-plotted as a function of four different crack driving force parameters, viz., (a) Kujawski’s K*, (b) two parameter ΔK*, (c) Walker’s ΔKw and (d) Foreman’s ΔKf. It was observed that Kujawski’s crack driving force parameter, K*, was correlating stress ratio effects better than all other models in all the three regimes of crack growth rates in this material. Further, all these models were employed to predict fatigue crack growth behaviour under a truncated FALSTAFF spectrum load sequence. It was observed that the total fatigue crack growth life estimated varied from about 25 blocks to about 75 blocks. Thus, the use of appropriate crack growth model appears to influence accuracy of life prediction under spectrum loads
3D Localisation of Target using Elevation Angle Algorithm with the use of Ground Radars
Get PDFA new novel method based on elevation angle algorithm (EAA) is proposed in this paper, to obtain 3D position
of target using range and azimuth measurements of two ground 2D radars. The EAA estimates optimal target
elevation angle wrt contributing radar by solving a non-linear optimisation problem using Levenberg-Marquardt
method in geo-centric frame such as earth-centred-earth-fixed. The target position in geodetic frame (WGS84) is
then obtained using slant range, azimuth and estimated elevation angle. The proposed method is evaluated using
simulated but realistic radar data and accuracy of estimated position is found to be comparable with true position
(error within acceptable limit). The method is also evaluated with real data from actual ground 2D radars and
estimated target position is found to be comparable with reference navigation data (GPS) on-board of target. For
each radar, corresponding Extended Kalman filter (EKF) is used to handle noisy, asynchronous measurements and to
provide estimated range and azimuth at common reference time for altitude estimation using proposed EAA method.
In case of real data, the estimated altitude is found to be comparable GPS altitude with error less than 5 % of true
altitude. From the study, it is found that EAA is suitable to estimate target position using measurements from only
two contributing asynchronous 2D radars in real-time as compared to some other techniques such triangulation and
Trilateration where at-least three radars are required to get the position of target. This method can be useful to utilise
network of vintage long range 2D radars to determine target position and to fill the gap wherever/whenever target
is out of detection range of 3D radars. In addition, EAA method is compared with commonly used methodology
such range only localisation and results are presented
Influence of geometric parameters on the bump foil bearing performance
No full textHigh-speed rotating system development has drawn considerable attention of the researchers, in the recent past. Foil bearings are one of the major contenders for such applications, particularly for high speed and low load rotating systems. In foil bearings, process fluid or air is used as the working medium and no additional lubricant is required. It is known from the published literature that the load capacity of foil bearings depend on the operating speed, viscosity of the medium, clearance, and stiffness of the foil apart from the geometric dimensions of the bearing. In case of foil bearing with given dimensions, clearance governs the magnitude of pressure developed, whereas stiffness dictates the change in radial clearance under the generated pressure. This article deals with the effect of stiffness, clearance, and its interaction on the bump foil bearings load-carrying capacity. For this study, four sets of foil bearings of the same geometry with two levels of stiffness and clearance values are fabricated. Experiments are carried out following two factor-two level factorial design approach under constant load and in each case, the lift-off speed is measured. The experimental output is analyzed using statistical techniques to evaluate the influence of parameters under consideration. The results indicate that clearance has the maximum influence on the lift-off speed/ load-carrying capacity, followed by interaction effect and stiffness. A regression model is developed based on the experimental values and model is validated using error analysis technique
Effect of Electrolyte Temperature and Anodization Time on Formation of TiO2 Nanotubes for Biomedical Applications
No full textWe have investigated the formation of self-organized titanium oxide nanotube layers by anodic oxidation on titanium alloys in electrolyte solutions with different temperatures (5, 10, 25, 30, 50 and 70 °C). Pore diameter and the wall thickness of nanotube arrays were controlled by varying anodization time and temperature. We have observed significant outcomes in the formation of TiO2 nanotube arrays at 25 °C with an average inner pore diameter of 125 nm, length of ∼250 nm, the wall thickness of 30 nm and an inter-tube space 35 nm. Nanotube arrays were smooth and circular without any defect in morphology. In addition, anodization of Commercially Pure Titanium (CP Ti) and titanium alloys (Ti-6Al-4 V, Ti-6Al-7Nb, Ti-13Nb-13Zr, and β-21 s) was carried out at optimized parameter to understand their significance on TiO2 nanotube arrays formation
Influence of Post-Weld Processing Techniques on Laser Beam-Welded Al–3Mg–0.25Sc Alloy Sheets
No full textFusion welding in aluminium alloys had always remained an issue for aero- and auto industries. An Al– 3Mg–0.25Sc alloy is classified as weldable aluminium alloys. In this study, two welding techniques, keyhole and conduction welding, have been used for joining Al–3Mg– 0.25Sc sheets of thickness 1.6 mm. Experiments were carried out using different beam diameter (0.16– 2 mm dia), beam power (2–4.5 kW) and laser head speed (ranging from 0.5 to 6 m/min). The results for all autogenous key- hole welding clearly demonstrated a drop in ductility (\ 0.8%) compare d to base metal for all beam power and welding speed combinations although the yield strength was reas onably good (175–180 MPa, i.e. [ 50% of base metal). Residual stress-induced distortions affected the final shape of the product, and for that, a suitable stress relief annealing was also required. Hereby, we chose two heat treatment schedules: (1) solution treatment and annealing and (2) retrogression and re-ageing. Retrogres- sion and re-ageing is a precipitation-controlled phe- nomenon and comprises of an intermediate annealing step between tempering and solutionizing temperature to dis- solve the nano-clusters present in the matrix (retrogression) and re-precipitating and growing them by ageing (re-age- ing). These two steps were repeated cyclically, and as a result, the strength (190 MPa) and ductility (* 9%) of the material were improved substantially. The improvement of ductility and strength was explained in detail in the light of microstructural studies
Tribo–Mechanical Properties of HVOF-Sprayed NiMoAl-Cr2AlC Composite Coatings.
No full textThe tribo-mechanical properties of NiMoAlCr2AlC MAX phase composite coatings on stainless steel substrate have been investigated. NiMoAl with different amounts of Cr2AlC (10, 20, 50 and 100 wt.%) were prepared by turbo-mixing and deposited by High-Velocity Oxy-Fuel (HVOF) method on stainless steel substrate. The phase composition, microstructure, chemical composition, tribological and mechanical properties of the coatings were analyzed using x-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy-Dispersive x-ray analysis (EDAX), pin-on-disk wear testing rig and nanohardness tester, respectively. The worn surfaces were analyzed by metallurgical optical microscope, FESEM and three-dimensional surface profiler to understand the wear behavior in detail. The addition of the Cr2AlC MAX phase in NiMoAl enhances the mechanical properties and reduces the surface roughness and porosity. NiMoAl-20 wt.% Cr2AlC and Cr2AlC coatings containing equal amounts of oxygen and carbon in the tribofilm show the low coefficient of friction (COF) and wear rate. The addition of the Cr2AlC MAX phase in the NiMoAl matrix up to 20 wt.% reduces the wear rate by one order of magnitude and enhances the coating life by 7000 twist fatigue cycles
Urban Heat Island studies: Current status in India and a comparison with the International studies
Get PDFUrbanization has resulted in many critical issues like increase in pollution levels, sudden climatic changes and the rise of temperature in the urban area, that is the formation of Urban Heat Islands (UHI). As the density of population rises, most of the land areas are being converted into cities and cities grows very rapidly. Due to the UHI eAect, the cities are becoming hotter day by day. In India, all the metropolitan cities are victims of UHI eAect and the severity of heat formation, necessitates research in this area. The present paper evaluates the trends of UHI studies in Indian cities and its out reach till 2018. Heat Island classiBcation, methods of studying UHI in India and their limitation are discussed. Eventually a comparison of new trends of UHI studies in the world and where India lacks its growth in UHI research are included in this paper. One of the Bndings is that numerical modelling studies are very limited in India in this Beld and more focus in this area is required
Role of SiC on mechanical and tribological behavior of Mg metal matrix composites prepared by powder metallurgy route
No full textThe present work involves the processing, mechanical and dry sliding wear behavior of silicon carbide (SiC) particles with magnesium (Mg) matrix. The amount of SiC reinforcement was 10 and 20 vol. %. The composites were produced using hot pressing at 5 MPa, 640 °C for 30 min. The density of Mg-SiC10 vol. % and Mg-SiC20 vol. % composites are 1.81 and 1.98 g/cm3, respectively. Microhardness and compressive strength of the composites was increased as the SiC content increases. Dry sliding wear test carried out at different load, sliding distance and sliding velocity having coefficient of friction in the range 0.39-0.53 and specific wear rate of 1.7×10−6 cm3/N m for Mg-SiC20 composites