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Solar selective coatings and materials for high-temperature solar thermal applications
No full textConcentrated Solar Power (CSP) technology harnesses the solar power to generate electricity using solar thermal absorbers. Due to the lack of solar thermal materials and components stable under the harsh conditions of central receivers, their operational temperature is limited to <600°C (well below the optimal value). While CSP has a great potential to produce electricity from the solar energy, high investment costs, and decreased fossil fuel prices have prevented to keep up a track with the roadmap of the International Energy Agency. In this chapter we summarize the latest innovative materials science approaches devoted to increase the efficiency of CSP plant by implementing higher operational temperatures, thereby reducing the levelized cost of electricity. We also address the roadmap for CSP absorbing surfaces and materials for high-temperature applications. Further, issues related to industrialization of solar absorber surfaces, their durability, and characterization protocols at elevated temperatures are discussed in brief
Stress detection from EEG using power ratio.
Get PDFStress correlates itself as a mental conscious and emotion within a person that influences mental ability and decision-making skills, which results in an inappropriate work. Studies have recently developed to detect the stress in a person while performing different tasks. One of the methods is through Electroencephalograph (EEG). These are the bioelectrical signals generated in a human body while performing the tasks and thus describes the activity of the brain. Any action taken by a person changes the properties of these signals. This present work focuses on the classification of baseline (relax) and stress detection using EEG sub-band power ratio as features. Support vector machine (SVM) classifier with different kernel function parameters and K-nearest neighbor (KNN) classifier with a different number of neighbors with holdout and 10-fold cross-validation technique were used to classify power ratio features in order to detect stress. To evaluate the classifier performance various performance metrics were used. It is observed that KNN with a number of neighbors as one, with Euclidean distance gives better performance in both validation techniques and also anterior frontal channel Fpl that is placed at the left side of the brain itself gives a good accuracy of 99.42%. The performance of the proposed method is verified on a publicly available mental arithmetic dataset where stress is induced while performing the mental cognitive workload i.e., mental serial subtraction
3D Localisation of Target using Elevation Angle Algorithm with the use of Ground Radars
No full textA 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
Damage Tolerance Capability of Retrogression and Re-aged 7010 Aluminum Alloy Under FALSTAFF Loading
No full textThe present work deals with the damage tolerance characteristics of high strength aluminum alloy tempered in T6 and reversion condition. The fatigue experiments were carried out by applying a service simulating load spectrum, i.e., standard mini FALSTAFF loading. The crack propagation speed was found to be lower and the total crack propagation life was longer by 22% for reversion-treated alloy. The crack growth was also predicted to be using two parameter crack driving force approach. The fatigue data of these treated alloys under constant amplitude loading at various stress ratios were analyzed to obtain crack growth law. The predicted crack growth behavior was conservative and followed similar trend in both the alloys as observed in experiments. Predicted results of reversion-treated alloy also showed longer crack growth life. The modified microstructure after reversion treatment was attributed for the observed improvement in damage tolerance capability
Selective properties of high-temperature stable spinel absorber coatings for concentrated solar thermal application
No full textIn concentrated solar thermal (CST) system, receiver tube is one of the key important elements in the photothermal conversion process. The high photothermal efficiency of the receiver tube greatly depends upon the coating type, angular selectiveness of the coating, and radiative, conductive and convective losses. Apart from the efficiency, cost-effectiveness of the components is the major hurdle for the CST system to make it a viable technology. In this regard, we have implemented wet-chemical based spinel absorber coatings in a tandem layer approach to make the coating more selective in terms of high absorptance (95%), low emissivity (13%) and wide angular selectiveness (0 to 60°). The coatings are tested for thermal stability and corrosion resistance to check their stability in open-air atmosphere condition. Further, the photothermal conversion efficiencies of the developed coatings are calculated at different temperatures ranging from 300 to 500 °C by considering the actual thermal emissivity values of the absorber coating at that particular temperature
Surface optimization of CVD grown silicon carbide interlayer on graphite for plasma sprayed yttria topcoat
No full textChemical Vapor Deposition (CVD) technique is employed to deposit uniform, smooth, and dense SiC interlayer over High-Density Graphite (HDG) substrate, as an interlayer for subsequent deposition of yttria (Y2O3) topcoat by Atmospheric Plasma Spray (APS) process. In any thermal spray process, since the bonding is purely mechanical interlocking, the surface roughening of smooth CVD grown SiC surface becomes essential. Different surface preparation techniques like alumina grit blasting, plasma etching, laser ablation, and chemical etching were attempted to create rough anchoring patterns on SiC surface. Chemical etching of SiC interlayer by using molten eutectic NaOH/KOH is found to be effective in introducing the desire anchoring sites for Y2O3 splats during plasma spraying. The microstructural features and surface roughness of CVD grown SiC and after subsequent surface roughening treatments were compared using SEM/EDS and profilometer, respectively. The performance and its durability evaluation were carried out by thermal cycling studies on Y2O3 coated samples with and without SiC interlayer at 1723 and 1823 K that shows considerable improvement in the life of plasma sprayed Y2O3 coating with SiC interlayer
‘Trigger-free’ self-healable electromagnetic shielding material assisted by co-doped graphene nanostructures
No full textThe repercussions of the miniaturisation and augmentation of modern electronics and telecommunication are the unwanted interferences that come along with it. In the search for a good EMI shield, nanotechnology has come a long way from metal-based EM wave reflector to now lightweight polymeric EM wave absorbers. In this study, we have developed a unique heterostructure by combining the electronic properties of MWNTs, “flower-like” MoS2, magnetic properties of Fe3O4 and graphene oxide (GO) sheets. This resulted in a superior EM shielding performance of −43.6 dB at 18 GHz with up to 96% absorption of EM waves. Additionally, the effect of two other different type of dopants in rGO@MoS2 namely, dielectric dopant (SiO2) and conducting dopant (Ag) was also studied apart from magnetic dopant (Fe3O4) to establish their effect on final shielding efficiency. It was observed that magnetic dopant exhibited highest absorption performance (96%) followed by dielectric dopant (90%). Since these materials have potential usage in high-end applications, we have attempted to develop a multifunctional material whereby we have modified the polymer matrix to develop a “trigger-free” self-healing polymer with up to 70% recovery of its original mechanical properties and nearly unaltered EMI shielding performance post healing. Such a unique multi-dimensional approach helps to improve the quality and lifetime of high-performance shielding materials which takes care of the fact that polymeric materials are mechanically weak compared to their metal counterparts
Effect of Microstructure on the Fatigue Crack Growth Behavior in Al–Zn–Mg–Cu Alloy.
No full textHigh-strength Al–Zn–Mg–Cu alloys are used in airframe structures, such as bulk heads, wing spars, and lug joints. In this investigation, the effect of RRA microstructure on the fatigue crack growth rate (FCGR) behavior is studied. The 7010 aluminum alloy was heat treated to two different conditions, i.e., T6 and RRA. The microstructure of the heat-treated alloy is characterized by using transmission electron microscope (TEM). The FCGR tests were performed as per ASTM E647 standard by using a 100 kN servo-hydraulic test machine. The tests were performed using standard compact tension (CT) specimens with a stress ratio, R = 0.7 using a sine wave form at 10 Hz in a standard laboratory air environment. The matrix microstructure of the RRA-treated alloy consists of fine scale η´ (MgZn2) precipitates with increased interparticle spacing when compared to closely packed η´ precipitates in the standard T6-treated alloy. The grain boundary precipitates are coarsened and discrete in the RRA-treated alloy, while it is continuous in T6 condition. An improvement in the threshold stress intensity factor range (ΔKth) by about 0.65 MPa√m is observed in RRA-treated alloy compared to the T6-treated alloy. The FCGR was observed to be lower by 2 times in RRA-treated alloy compared to T6-treated alloy over the major portion of FCGR curve. The increased free slipping distance between the matrix precipitates in RRA-treated alloy is correlated to the improved fatigue crack growth resistance of the RRA-treated aluminum alloy
An experimental investigation of turbo-ramjet engine intake at mach 4.
No full textThe objective of this research is to investigate the axisymmetric supersonic intake SR-71 scaled model at a Mach number of 4. To understand this mixed compression intake and quality of inlet flow, static and total pressure measurement in the duct are measured. Also, the color schlieren technique is used to observe the shock effects on the external flow. To improve the pressure recovery of intake, surface correction of the cone is attempted. By using taper plug different blockage (0%, 30%,60%,90%) area of exit is obtained to locate normal shock in throat for minimum loss of pressure. Design model, instrumentation, intake operation, inlet buzz, and data analysis are covered in detail in this research
Present status and future prospects of plasma sprayed multilayered thermal barrier coating systems
No full textThermal 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)