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Structural, magnetic and NO2 gas sensing property of CuO nanoparticles.
No full textCupric oxide (CuO) nanoparticles are synthesized by the oxidation of Cu/Cu2O, which is obtained by the chemical reduction of Cu2+ ions with ascorbic acid. XRD pattern confirmed the formation of CuO, and FE-SEM image shows the clusters consisting of 25–30 nm sized particles. The band gap energy (3.7 eV) from optical absorption spectra is blue shifted to that of bulk values. The Néel temperature, TN ≈ 230 K for paramagnetic to antiferromagnetic transition was clearly seen. The magnetic hysteresis loops at 5 K showed weak ferromagnetic behavior. Based on the dc electrical conductivity (300–500 K), the apparent activation energy was 0.36 eV. The NO2 gas sensing property of CuO was reasonably good in the temperature range of 200–300 °C, and the sensitivity increased with an increase in gas concentration but the effect of temperature is marginal
Performance evaluation and durability studies of W/WAlSiN/SiON/SiO2 based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing.
No full textWe report a solar selective coating of W/WAlSiN/SiON/SiO2 fabricated using a Four-Cathode Reactive Unbalanced Direct Current (DC) magnetron sputtering system with high thermal stability, good durability and resistance to outdoor testing conditions. The coating also exhibits superior mechanical properties (Hardness ∼12 GPa). In addition, thermal shock tests at high temperatures and solar accelerated ageing measurements are investigated in-depth to analyze the performance of the solar absorber coating. The thermal shock tests of the samples at various temperatures in the range of 500–600 °C depict the excellent thermophysical resistance of the as-deposited samples. To test the thermal durability of the solar absorber coating, we applied 200 cycles of solar accelerated ageing on the samples using a solar accelerated ageing facility with concentrated flux density varying from 50 to 250 kW/m2. These cycles have been defined to replicate real high solar flux and temperature on the front side of the samples along with high cooling and heating rates, reproducing the abrupt variations of solar irradiation due to cloudy weather and subsequent thermal shocks for a given receiver. Overall, the durability tests of the solar absorber carried out under various conditions indicate a minimal change in the optical properties (Δα = 0.002 and Δε = 0), thus, making it a potential candidate for high-temperature solar thermal applications
Anatase TiO2 decorated CuCr2O4 nanocomposite: A versatile photocatalyst under domestic LED light irradiation
No full textThe rutile and anatase polymorphs of TiO2 are the most extensively studied photocatalyst materials with the efficient absorption in the violet to near ultra violet region of the electromagnetic spectrum, which boost tremendous research endeavors in increasing the photocatalytic activity of TiO2 under visible light sources through rational modifications. Here, we report the astonishing performance of CuCr2O4(CCO)/anatase-TiO2 nanocomposite as a Fenton like catalyst with potential impact for sustainable design and environmental protection. All the materials were thoroughly characterized by several physico chemical techniques. CCO/TiO2 nanocomposite obtained by heat-treatment at 400 °C is found to exhibit high performance towards degradation of azo dyes like methylene blue (MB), rhodamine B (RhB) and methyl orange (MO), antibiotics like tetracycline hydrochloride and norfloxacine, and a promising Pt-free candidate for photoelectrocatalytic oxygen evolution reaction under domestic light emitting diode (LED) light irradiation. CCO/TiO2 shows high recycling activity and chemical stability. Under domestic visible LED light irradiation, the electrons are photoexcited from the conduction band of CCO to that of TiO2 resulting in enhanced charge separation eventually facilitating the catalytic performance of the nanocomposite. TiO2 plays two primordial roles, firstly, it acts as an electron receiver to improve the charge separation in the nanocomposite and secondly, it participates in the Fenton like reaction
Failure of flexible couplings in environmental control system (ECS) of an aircraft.
No full textThere was an incidence of failure of flexible coupling joining the pipelines in environmental control system (ECS) of a military aircraft. Examination revealed that the sleeves of the coupling got detached from the assembly because of fracture in all the rivets with the steel locks. The rivets were made of Al-alloy of specification 5083. Microscopy and fractography studies confirmed that the failure mechanism in the rivets was exfoliation corrosion. In-situ composition analysis of the corrosion products on the fracture surfaces of the rivets showed presence of chlorine (Cl) in quantities as high as 8.9 wt%. In addition, deposits of foreign material were found present on the steel lock surface surrounding the rivets. The observed foreign material contained sodium (Na), magnesium (Mg) and chlorine (Cl) in concentrations as high as 16.3, 10.2 and 14.0 wt% respectively. Considering the application environment, presence of Na, Mg and Cl in such high quantities appeared to be unrealistic. Examination of service records of the ECS revealed that during each time of maintenance, leak checks were performed on the pipe assemblies. As per the standard operating procedure (SOP), a proprietary solution was recommended for this purpose. But, over the years, the manufacturer changed over to usage of commonly used soap solution for leak checks. Chemical analysis showed that the soap solution contained Na, Mg and Cl in large quantities. Failure of the Al-alloy rivets by exfoliation corrosion mechanism was facilitated due to usage of soap solution containing these corrosion species. The root cause responsible for creating the condition for physical failure to occur has been discussed in this paper
Performance trends of a generic small gas turbine engine
No full textSmall gas turbine engines are increasingly used in cruise missile applications. In the design stage of these engines, aero-thermodynamic models are used to evaluate the expected performance of the engine for a given set of component characteristics. The throttle characteristics and altitude-Mach number characteristics of the engine are iteratively analyzed using this model. This paper describes the use of such a model to show the expected performance of a set of design choices at different altitudes and Mach numbers. These small engines are operated at maximum possible Turbine Inlet Temperatures (TIT) for maximum thrust. Theoretical relations that give the slope of the operating line for constant turbine inlet temperature operation is derived. Using these expressions, the reduction of stability at high altitude and low Mach number is shown
Poly (ε-caprolactone)-based electrospun nano-featured substrate for tissue engineering applications: a review
No full textThe restoration of normal functioning of damaged body tissues is one of the major objectives of tissue engineering. Scaffolds are generally used as artificial supports and as substrates for regenerating new tissues and should closely mimic natural extracellular matrix (ECM). The materials used for fabricating scaffolds must be biocompatible, non-cytotoxic and bioabsorbable/biodegradable. For this application, specifically biopolymers such as PLA, PGA, PTMC, PCL etc. satisfying the above criteria are promising materials. Poly(ε-caprolactone) (PCL) is one such potential candidate which can be blended with other materials forming blends, copolymers and composites with the essential physiochemical and mechanical properties as per the requirement. Nanofibrous scaffolds are fabricated by various techniques such as template synthesis, fiber drawing, phase separation, self-assembly, electrospinning etc. Among which electrospinning is the most popular and versatile technique. It is a clean, simple, tunable and viable technique for fabrication of polymer-based nanofibrous scaffolds. The design and fabrication of electrospun nanofibrous scaffolds are of intense research interest over the recent years. These scaffolds offer a unique architecture at nano-scale with desired porosity for selective movement of small molecules and form a suitable three-dimensional matrix similar to ECM. This review focuses on PCL synthesis, modifications, properties and scaffold fabrication techniques aiming at the targeted tissue engineering applications
Vibration Reduction in Indigenous Wankel Rotary Combustion Engine with Structured Layer Damping
No full textRotary engines are simpler in design and operation compared to the gas turbines. Rotary engines propel many monoplanes, power hang gliders, and unmanned aerial vehicles (UAV). In an indigenization effort, a 65 hp Wankel rotary combustion engine (WRCE) was successfully developed in the country for a wheeled version of Nishant UAV. As a part of the testing and certification process, three engines were required to be tested in the test bed for a stipulated number of hours. The engine was mounted in the test bed on two cantilever bolts in horizontal and two in the vertical direction with equi-frequency anti-shock mounts. During testing without the alternator, it was observed that the vibrations are higher with 1X amplitude of 24 g. To identify the source of vibration, a detailed modal analysis was carried out. Impact test data showed the existence of dominating frequency around 138 Hz. To reduce the vibrations, the engine mount is modified suitably, and structured layer damping is introduced between the engine mount and support structure. This modification resulted in increased damping leading to vibration reduction to the acceptable level. Testing of Wankel engine with alternator up to the required speed was completed successfully using the structured layer damping method
Enhancement in wind tunnel data acquisition system using NI-LabVIEW
No full textWind tunnel data acquisition possess challenging problem in terms of acquiring data at multiple sampling frequency, limited tunnel test time, requirement of signal conditioning, synchronization with the tunnel events, multi-mode tunnel operation and various categories of measurement quantities. Looking the requirements of CSIR-NAL 1.2m Trisonic wind tunnel, NI-LabVIEW based data acquisition system has been configured and enhanced LabVIEW based software program is implemented. In this paper an attempt is made to explain the concept and complexities involved in wind tunnel data acquisition system development. Typical force data from six component strain gauge balance and tunnel free stream data were acquired and monitored using the developed system. LabVIEW based single program is written to enable user-friendly data acquisition system to cater to the needs of the wind tunnel users. LabVIEW based code is developed to fulfill the complete data acquisition requirements like continuous data acquisition, step-mode data acquisition, system calibration mode, balance tare data, check calibration data, model natural frequency and transducer calibration through a single program. Present data acquisition system suits for any wind tunnel across the globe
Creep-fatigue behavior of a newly developed ultra-supercritical steam turbine grade nickel-based superalloy, Haynes 282
No full textMost engineering components used in gas/steam turbines are exposed to a range of complex loading conditions resulting from startup and shutdown procedures. These loading conditions involve superimposition of time-dependent creep on cyclic fatigue and can be simulated by properly designed high-temperature creep-fatigue tests. Creep-fatigue interaction is a function of duration and position of dwell in the loading waveform, and the material microstructure. The objective of this work is to investigate the creep-fatigue interaction response of a newly developed γ′-strengthened wrought nickel-based superalloy (HAYNES 282), which has a potential application in advanced ultra-supercritical steam turbines. Creep-fatigue tests are conducted at 760°C with strain dwell either at tensile peak or compressive peak or at both tensile and compressive peak positions for different dwell times of 100 and 1,000 s. The test results are analyzed with respect to evolutions of peak stress, stress amplitude, stress relaxation, hysteresis loop, inelastic strain energy density, and degree of softening. Degree of softening is found to increase with dwell position at tensile, compressive, and both peaks in that order. Tests with dwell at both tensile and compressive peak positions are found to be the most damaging, showing the least life. Between tensile dwell and compressive dwell tests, interestingly, those with compressive dwell show a significantly reduced life. Increasing dwell time aggravates the damaging effect manifold. The mechanism of fracture at the end of life is illustrated with fractographic characterization
Unfolding the effects of tuft density on compression after impact properties in unidirectional carbon/epoxy composite laminates
No full textPost impact compressive residual strength of epoxy-based composite laminates is studied in the presence of through-thickness reinforcement (TTR). The tufting technique is used to introduce TTR in compact carbon unidirectional (UD) composites. Composite laminates are tufted using Kevlar thread with different tuft density by varying tuft pitch and spacing. The specimens are impacted with low-velocity impact to achieve barely visible impact damage (BVID). The damaged area is quantified using the ultrasonic C-scan method. Tufted specimens exhibited a significant reduction in the damaged area. The reduction in damage area is about 26% to 51% depending upon the tuft density. Residual strength post impact is determined by compression after impact (CAI) test. Upon increasing the tuft density up to 0.56%, the damaged area decreases by 51%, and CAI strength increases by 43%. Above this tuft density, damage area slightly decreases and CAI strength remains almost the same. The improvement in CAI strength is due to an increase in apparent interlaminar strength attributed to the enhancement in bridging effect due to TTR. Different failure modes such as delamination, fiber crushing, kink-band formation, etc. are observed in both the untufted and tufted specimens