Kuldeep Singh

Microwave Absorption Behavior of Core−Shell Structured Poly (3,4-Ethylenedioxy Thiophene)−Barium Ferrite Nanocomposites

The present paper reports the complex permittivity, permeability, and microwave absorption properties of core shell type poly (3,4-ethylenedioxy thiophene) (PEDOT) nanocomposite with barium ferrite, synthesized by in situ emulsion polymerization, in the 12.4-18 GHz frequency range. High-resolution transmission electron microscopy (HRTEM) studies reveal the formation of core-shell type morphology with ferrite particles (60-80 nm) as the center while the polymer (PEDOT) formulates the outer shell of the composite. The presence of barium ferrite nanoparticles in the polymer matrix includes the magnetic losses, which mainly arise from the magnetic hysteresis, domain-wall displacement, and eddy current loss. The higher dielectric (epsilon = 23.5) and magnetic loss (micro = 0.22) contributes to the microwave absorption value of 22.5 dB (>99% attenuation) and are found to increase with the amount of ferrite constituents. The polymer was further characterized through Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD).

Conjugated polymer nanocomposites: Synthesis, dielectric, and microwave absorption studies

Nanocomposites of polyaniline with barium ferrite and titanium dioxide (TiO2) are synthesized via in situ emulsion polymerization. The transmission electron microscopy (TEM) and high resolution TEM result shows the formation of array of nanoparticles encapsulated within the polymer chains during the synthesis process. The high value of microwave absorption, 58dB (>99.999% attenuation) results from the combined effect of the nanoparticles and the polymer matrix. The amount of barium ferrite has the profound effect on permittivity (e), permeability (μ), and microwave absorption of the nanocomposite. The contribution to the absorption value comes mainly due the magnetic losses (μ″) in barium ferrite and dielectric losses (e″) in TiO2 and polyaniline.

Designing of Nano Composites of Conducting Polymers for EMI Shielding

Enormous progress in nanotechnology has made electronic systems smaller and has increased the density of electrical components within an instrument. The operating frequencies of signals in these systems are also increasing and have created a new kind of problem called electromagnetic interference (EMI). To provide an adequate solution for the EMI problem, the shielding or absorbing of the electromagnetic field is taken into account. It is observed that the high conductivity and dielectric constant of the materials contribute to high EMI shielding efficiency (SE). This article is an evaluation of the ferrite based conducting polymer nanocomposite and underlines the complex interplay of its intrinsic properties with EMI shielding. The unique properties of nanostructured ferrite offer excellent prospects for designing a new kind of shielding materials. The absorption loss in the material is caused by the heat loss under the action between electric dipole and/or magnetic dipole in the shielding material and the electromagnetic field so that the absorption loss is the function of conductivity and the magnetic permeability of the material. The designing of ferrite based conducting polymer nanocomposites increases the shielding effectiveness. Conducting and magnetic properties of conducing polymer-ferrite nanocomposites can be tuned by suitable selection of polymerization conditions and controlled addition of ferrite nanoparticles. The contribution to the absorption value comes mainly due the magnetic losses (┤ ) and dielectric losses (┝ ). The dependence of SEA on magnetic permeability and conductivity demonstrates that better absorption value has been obtained for material with higher conductivity and magnetization. Therefore, it has been concluded that the incorporation of magnetic and dielectric fillers in the polymer matrix lead to better absorbing material which make them futuristic radar absorbing material. This chapter examines the development of ferromagnetic conducting polymer nanocomposite in the context of its application as microwave absorber and concludes with some observations.

Polymer-Graphene Nanocomposites: Preparation, Characterization, Properties, and Applications

Carbon the 6th element in the periodic tables has always remains a fascinating material to the researcher and technologist. Diamond, graphite, fullerenes, carbon nanotubes and newly dis‐ covered graphene are the most studied allotropes of the carbon family. The significance of the these material can be understand as the discovery of fullerene and graphene has been awarded noble prizes in the years 1996 and 2010 to Curl, Kroto & Smalley and Geim & Novalec, respec‐ tively. After the flood of publications on graphite intercalated [1], fullerenes (1985) [2], and car‐ bon nanotubes (1991) [3], graphene have been the subject of countless publications since 2004 [4,5]. Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, completely conjugated sp2 hybridized planar structure and is a basic build‐ ing block for graphitic materials of all other dimensionalities (Figure 1). It can be wrapped up into 0D fullerenes, rolled into 1D nanotube or stacked into 3D graphite.

Prediction of film cooling effectiveness over a flat plate from film heating studies

ABSTRACT Film cooling is widely used to protect surfaces exposed to gases at a high temperature in gas turbine engines. Film heating is the reverse of film cooling, where hot secondary fluid is injected onto the walls to protect against a relatively cold mainstream. In the literature, the latter has often been used as an experimental analogue of the former, since mainstream flow rates are substantially higher, and it is relatively simpler to heat the smaller stream of secondary fluid for experiments. In this paper, the results obtained from a numerical study of film cooling and film heating over a flat plate through single-slot injection are presented. Since the objective of the work is to evaluate the suitability of film heating as a proxy for film cooling, it was decided to keep computational simple, using two-dimensional simulations. The effect of a density ratio of injectant-to-mainstream in the range of 0.2–5 is studied numerically to cover film heating and film cooling. Numerical simulations were carried out for three blowing ratios, M = 1, 2, and 3 at a fixed mainstream Reynolds number of 1.5 × 105 for three injection angles, 30°, 45°, and 60°. Numerical simulations were also carried out for a wide range of momentum flux ratio for film heating and film cooling at an injection angle of 30°. The results show that film heating and film cooling are not equivalent, especially when the density ratio deviates from unity substantially. Based on numerical study, it appears possible to predict film cooling effectiveness from film heating effectiveness for a wide range of density ratios, even though the effectiveness values obtained in regard to film cooling and film heating differ significantly.

A Numerical Study on the 2D Film Cooling of a Flat Surface

In this article, the results obtained from a detailed numerical investigation of 2D film cooling over a flat plate through single-slot injection are presented. The effects of mainstream Reynolds number, blowing ratio, density ratio, and injection angle on the effectiveness of film cooling were investigated in the present work. Numerical simulations were carried over a wide range of density ratio ranging from 1.1 to 5 at two mainstream Reynolds numbers (8 × 104 and 1.5 × 105), three blowing ratios (ranging from 1 to 3), and six injection angles (ranging from 15° to 90°). The results show that at lower injection angles of 15°–45°, maximum film-cooling effectiveness occurs at a particular value of velocity ratio which is found to be independent of mainstream Reynolds number, blowing ratio, and density ratio. Based on a combined effect analysis of blowing ratio, density ratio, and injection angle, a relation was obtained for velocity ratio that gives an optimum film-cooling effectiveness.

Numerical investigation of film cooling on a 2D corrugated surface

ABSTRACT A detailed numerical study on the film cooling of a corrugated surface through a single slot has been presented in this paper. The effects of the blowing ratio, density ratio (DR), and injection angle on the film cooling of the corrugated surface are discussed. Numerical simulations are carried out over a wide range of DRs ranging from 0.2 to 5.0 at a fixed mainstream Reynolds number of 1.5u2009×u2009105, three blowing ratios of 1, 2, and 3, and five injection angles ranging from 30° to 90°. Results show that the velocity profile on a corrugated surface is strongly influenced by the injection of the secondary fluid. It is observed that the film cooling effectiveness of the corrugated surface increases monotonically with an increase in the blowing ratio. The density ratio and injection angle also have a strong influence on the film cooling.