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Oxidative stabilization studies on pretreated polyacrylonitrile precursor fiber suitable for carbon fiber production
No full textPolyacrylonitrile (PAN) precursor fiber is the major precursor in demand for the production of carbon fiber. The conversion of PAN fiber to carbon fiber involves heat treatment of PAN fiber in different process condition at high temperatu re ranging from 200 to 1500 °C. The first step of heat treatment is oxidative stabilization of PAN fiber by controlled heating in air atmosphere at the temperature range 200-280 °C. Oxidative stabilization is a very slow process and the kinetics of stabilization depends on various parameters like comonomer composition in PAN copolymer, type of heat treatment atmosphere, heating rates, precursor fiber characteristics etc. The untreated and chemically treated precursor fiber characteristics are studied in detail during heat treatment under air atmosphere and effect of pretreatment on oxidative stabilization is studied using DSC, FTIR, elemental analysis and density measurements. Aqueous solution of Guanidine carbonate, ammonia and ammonium iodide are used for pretreating the precursor fiber prior to heat treatment. Chemical pretreatment of precursor fiber with guanidine carbonate and ammonia are found to help in achieving the optimum properties during oxidative stabilization
Nickel doped cobaltite spinel as a solar selective absorber coating for efficient photothermal conversion with a low thermal radiative loss at high operating temperatures
No full textConcentrated Solar Thermal (CST) system efficiency depends mainly on the operating temperature. One of the key components in the CST system is the receiver tube to attain higher temperatures, where the challenge remains on developing a solar absorber coating with high photothermal conversion and thermal stability at high temperatures. Nickel doped cobaltite (NixCo3-xO4; 0 ≤ x ≥ 1) thin film has been developed with spinel oxide phase on top of stainless steel substrates using a simple wet-chemical dip coating method as a base absorber layer (absorptance, α = 0.92; emittance, ε = 0.14). On top of the base absorber layer, coating integrated with silica (SiO2) as an optical enhancement layer (OPEL) has been deposited to make the coating more selective (α = 0.94 and ε = 0.13). A thorough investigation has been done to characterize the samples through UV–Vis–NIR spectrophotometer, Fourier transform infra-red spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetric analyzer for the optical and physiochemical properties. Besides, the optimized spinel coating exhibits a low radiative loss with a minimum thermal emissivity of 0.07 at 100 °C and 0.18 at 500 °C, which indicates that the nickel cobaltite spinels are a very good candidate for high temperature solar selective applications
Influence of thermal insulation and wind velocity on the SMA actuator for morphing applications
No full textThis paper presents the modeling and simulation of shape memory alloy (SMA) wire actuators for morphing micro air vehicles (MAVs) when exposed to high-velocity wind during flight. The specific operating conditions include thermal insulation, varying convective heat-transfer coefficients due to wind velocity, aerodynamic loads, and operation from MAV battery. Application-oriented modeling parameters were determined from a flyable morphing MAV. The simulation could dynamically generate the morphing angle as a function of the electrical input pulse duty cycle. The model showed that compared with 10 % duty cycle, a 25 % duty cycle achieves an energy saving of 33 % and an increase in actuation speed of 3.7 times. Further, increasing the duty cycle has a negligible improvement in energy saving, but the actuation rate is increased by 15.8 times. The SIMULINK® model, which was validated through the ground test, would help in the design of SMA actuators and controllers for aerospace vehicles and automobiles
Simulation of flapping wings subjected to gusty inflow
No full textOrnithopters and entomopters should be insensitive to the gusty environment during outdoor operations. Hence, it becomes imperative to understand their behaviour under the influence of gust for ensuring stable flight. In light of this, the present numerical study focused on understanding the aerodynamics of flapping wings with five different planform shapes under the influence of a spatiotemporally varying frontal gust. 3D, unsteady, laminar, and incompressible Navier-Stokes equations were solved using finite volume formulation. A canonical case of asymmetric 1 degree of freedom (DoF) flapping kinematics was considered. Horizontal and vertical force patterns in constant and gusty inflow conditions were numerically computed and compared. Findings were analyzed quantitatively by comparing the differences in the instantaneous force patterns, ordinal scoring approach, and phase space plots. Qualitative comparisons were made based on plots of vortex structures and surface pressure contours for constant and gusty inflow conditions for wings with different planform shapes. Spanwise Lagrangian Coherent Structures (LCS) of all the five wings were also compared. Studies revealed that the elliptical wing exhibited low sensitivity and inverse semi-elliptical wing exhibited high sensitivity to the gusty inflow. Rectangular, triangular and semi-elliptical shaped wings were moderately sensitive to the gusty inflow. This finding, within the limitations of the flapping kinematics and simulation conditions considered for the present study, supported the fact that many natural flyers like forest raptors, non-migratory passerines, pheasants, and partridges have adopted elliptical wing planform for efficient flight
Fabrication and experimentation of diffuser augmented wind turbine
No full textWind Energy is turning into a big supply of
renewable energy throughout the globe. This ever increasing field can probably reach the limit of accessibility and utility with the wind energy facility sites and size of the turbine itself. Therefore,
it's needed to develop wind capturing devices that may produce energy within the locations wherever typical horizontal axis wind turbines (HAWTs) are too unrealistic to put in and operate. A diffuser augmented wind turbine (DAWT) is one such invention.
DAWTs increase the ability output of the rotor by increasing the wind speed into the rotor employing a duct. The main objective of the project is to analyze the flow through the diffuser by placing it in wind tunnel and further the results are compared with the
computational results.
The purpose of investigating the flow through, the diffuser is to find out the behavior of wind flow at the throat region of the diffuser. Numerical analysis of diffuser is performed using the tool ANSYS FLUENT 15 and then by experimentation in wind tunnel.
Experiments were carried out for investigating the flow pattern inside the circular profile diffuser of radius 60mm, Throat diameter of 200mm, inlet and outlet diameter of diffuser is 320mm. Pitot tubes are inserted on the rake and then mount on the throat region of diffuser for flow measurement in that region.
Differential pressure transducers which gives voltage output are used for sensing the pressures from Pitot tubes, static tubes which is mount on surface of test section of tunnel and PS tube which is used for reference velocity. Further obtained pressure will be converted to velocity and get the required result. After completion
of computational and experimental work comparable results were obtained
Assessing grey literature use by researchers of council for scientific and industrial research
No full textThe present study on the use of both external and internal grey literature by CSIR researchers shows that technical reports are most used followed by doctoral theses. It was found that engineering and physical sciences laboratories use more internal grey literature than chemical and biological sciences laboratories. These and other findings help is framing content development policy for technical grey literature, framing policies for internal grey literature archiving, designing digital repository framework to archive internally generated grey literature and improve access and devise ways to enhance their visibility and use
Introduction: Design, Testing, Identification and Validation
No full textIt is well-known fact that most of the smaller aircraft can be manually controlled since the loads on the flight control surfaces are less and well within the handling capability of pilot. However, to reduce the pilot’s workload, hydraulic boosters are used in such aircraft with lower operating pressures. Redundancy of hydraulic system is not an essential consideration in such applications since the aircraft can be fully controlled by the pilot in the event of hydraulic power failures. However, many modern-day aircraft with large take-off weights and propelled by jet engines result in control loads which go beyond pilot’s handling capability and positively calls for a powered flight control system. Further, this powered flight control system gets more complicated due to the interfacing of automatic flight control system (AFCS). Factors like reliability and high response characteristics with high operating load holding features required for the flight control operation have inadvertently resulted in the use of hydraulic systems in modern-day aircraft. These systems are used in conjunction with electrical interfaces like electrically operated direction control valves and sensors for precision actuation of the flight control surface. Hence, the system in whole is referred to as electro-hydraulic actuation systems
Function space formulation of the 3-noded distorted Timoshenko metric beam element
No full textThe 3-noded metric Timoshenko beam element with an offset of the internal node from the element centre is used here to demonstrate the best-fit paradigm using function space formulation under locking and mesh distortion. The best-fit paradigm follows from the projection theorem describing finite element analysis which shows that the stresses computed by the displacement finite element procedure are the best approximation of the true stresses at an element level as well as global level. In this paper, closed form best-fit solutions are arrived for the 3-noded Timoshenko beam element through function space formulation by combining field consistency requirements and distortion effects for the element modelled in metric Cartesian coordinates. It is demonstrated through projection theorems how lock-free best-fit solutions are arrived even under mesh distortion by using a consistent definition for the shear strain field. It is shown how the field consistency enforced finite element solution differ from the best-fit solution by an extraneous response resulting from an additional spurious force vector. However, it can be observed that when the extraneous forces vanish fortuitously, the field consistent solution coincides with the best-fit strain solution
Dielectric Properties of γ-Iirradiated, Stretched, and Poled PVDF Thin Films
No full textThe effects of γ‐irradiation on the dielectric properties of stretched and poled polyvinylidene fluoride thin films synthesized by solvent cast method are reported. The films are subjected to γ‐irradiation with different doses (25, 50, and 75 kGy). XRD pattern is obtained to identify the presence of α/β phases. Dielectric constant and loss values of the stretched and poled films have been measured, before and after irradiation, and their nature of variation has been studied. β phase is retained even after the irradiation thereby confirming that the radiation damage is not significant. The dielectric loss is minimum in the frequency range 102 to104 Hz, giving the preferable frequency range of operation for device
Recurrence studies of insect-sized flapping wings in inclined-stroke plane under gusty conditions
No full textGlobal recurrence plots (GRPs) and windowed recurrence quantification analysis (WRQA) are two recurrence paradigms which find wide applications to detect the onset of instability in a dynamic system. The present work reports the attempt to employ these recurrence paradigms to assess the effect of frontal gust on the force patterns of an insect-sized flapping wing in the inclined-stroke plane. Horizontal and vertical forces generated by the flapping wing in the presence of gusts of the form uGuw=u∞uw+(uguw)sin(2πfgfwt) were numerically estimated in the 2D reference frame for Re = 150. Nine gusts with combinations of the ratio of gust frequency to wing’s flapping frequency, fg/fw = 0.1, 0.5 and 1 and ratio of gust velocity amplitude to root mean square averaged flapping velocity, ug/uw = 0.1, 0.5 and 1 were considered. Recurrence studies of the forces were carried out to find out the gusty condition, which would trigger an onset of unstable behaviour. Studies indicated a possible onset of instability in the force patterns for gust with fg/fw = 0.1 and ug/uw = 1. The onset of unstable behaviour was prominently captured by WRQA of the vertical force coefficient based on determinism (DET) and laminarity (LAM) serie