Grinding of aluminium silicon carbide metal matrix composite materials by electrolytic in-process dressing grinding

The grinding cost of metal matrix composite materials is more due to low removal rates and high rates of wear of super abrasive wheels. This electrolytic in-process dressing (ELID) technique uses a metal-bonded grinding wheel that is electrolytically dressed during the grinding process for abrasives that protrude continuously from super abrasive wheels. This research carries out ELID grinding using various current duty ratios and conventional grinding of 10% SiC_p reinforced 2,124 aluminium composite materials. Normal forces and tangential forces are monitored. Surface roughness of the ground surface, Vickers hardness numbers and metal removal rate (MRR) are measured. The results show that the cutting forces in the ELID grinding are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of grinding wheel and are less than conventional grinding forces. A smoother surface can be obtained at high current duty ratio in ELID grinding. The micro-hardness is reduced at high current duty ratio. In ELID, the MRR increases at high current duty ratio. The results of this investigation are presented in this paper.     

Electrochemical investigation of the roles of oxyanions in chemical–mechanical planarization of tantalum and tantalum nitride

Nitrate, sulfate, and phosphate oxyanions are shown to serve as effective surface-modifying agents for low-pressure chemical–mechanical planarization (CMP) of Ta and TaN barrier layers of interconnect structures. The surface reactions that form the basis of this CMP strategy are investigated using cyclic voltammetry, open circuit potential and polarization resistance measurements, and impedance spectroscopy. The results suggest that forming structurally weak layers of surface oxides is crucial to chemically controlling the CMP of Ta/TaN at low polish-pressures. It is shown that in oxyanion-based slurries, this can be accomplished by modifying the sample surfaces with anion-incorporated oxide films of Ta or TaN, which, in turn, can readily be removed with moderate abrasion. Electrochemical results elaborate the reaction mechanisms that lead to anion-modified oxides, such as Ta₂O_5(1−x)(NO₃)_10x , Ta₂O_5(1−x)(SO₄)_5x , and Ta₂O_5(1−x)(PO₄)_10x/3 on both Ta and TaN surfaces in pH-controlled solutions of KNO₃, K₂SO₄, and KH₂PO₄ solutions, respectively.     

Encapsulation of hydrophobic drugs in a copolymer: Glass transition behavior and miscibility evaluation

The knowledge of glass transition temperatures T_g in drug + polymer systems is indispensable for drug encapsulation. T_g values as a function of composition make possible the determination whether a given polymer is miscible or compatible with the drug and whether the polymer will provide release of the drug into organism within an acceptable rate range. We have used differential scanning calorimetry and Fourier‐transform infrared spectroscopy to evaluate miscibility in solid dispersions of the drugs carvedilol, itraconazole, nevirapine, and nimodipine in the pharmaceutical grade copolymer poly(vinyl pyrrolidone‐co‐vinyl acetate) (PLS‐630 Copovidone). Successful drug encapsulation is discussed in terms of thermophysical behavior (suppression of crystallization, negative excess volumes of mixing) and intermolecular interactions (concentrations of proton donating/accepting groups) in drug + polymer systems. Several equations were applied to the complex s‐shaped T_g(?) patterns obtained (? being the mass fraction of the drug). The best agreement of calculations with experiment is achieved using a recently proposed three‐parameter equation, symmetric with respect to the equal concentration of both components. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Bus encoder design for reduced crosstalk,power and area in coupled VLSI interconnects

This research work presents a novel circuit for simultaneous reduction of power, crosstalk and area using bus encoding technique in RC modeled VLSI interconnect. Bus-invert method is used to reduce inter-wire coupling, which is actually responsible for crosstalk, delay and power dissipation in coupled interconnects. The proposed method focuses on simplified and improved encoder circuit for 4, 8 and 16 coupled lines. In past, the researchers developed encoders that usually focused on minimizing power dissipation and/or crosstalk, thereby paying heavy penalty in terms of chip area. However, the proposed encoder and decoder while significantly reducing crosstalk demonstrates an overall reduction of power dissipation by 68.76% through drastically limiting switching activity. Furthermore, while reducing the complexity, chip area and transistor count of the circuit is reduced by more than 57%.     

Non Data Aided SNR Estimation for OFDM Signals in Frequency Selective Fading Channels

This paper deals with the problem of non data aided (NDA) signal to noise ratio (SNR) estimation of OFDM signals transmitted through unknown multipath fading channel. Most of present day’s SNR estimators are based on the knowledge of pilot sequences which is not applicable in some contexts such as cognitive radio for example. Moreover in Multipath fading channels SNR also depends on frequency offset which is caused by mismatch between the oscillator in the transmitter and that in the receiver. Previous NDA SNR estimation schemes assumed a perfect synchronization at reception (i.e. τ = 0 and ${\varepsilon = 0}$ ) which results estimation of SNR with less accuracy. The frequency offset attenuates the desired signal and causes intercarrier interference, thus reducing the SNR. In this paper we propose a new NDA SNR estimator which uses periodic redundancy induced by the cyclic prefix, considering SNR degradation due to frequency offset ( ${\varepsilon}$ ).     

Measurement of thermal conductivity of fluid using single and dual wire transient techniques

A modified measurement device to measure thermal conductivity of fluids using transient hot-wire technique has been designed, developed, tested and presented in this paper. The equipment is designed such that the thermal conductivity could be measured using both single wire sensor of different length and dual wire sensor. The sensor, which is also a heater, is a platinum micro-wire of 50 μm diameter. The influence of wire length on the measurement of thermal conductivity of fluids is tested using two single wires of length 50 mm and 100 mm. The thermal conductivity is also measured using a dual hot wire arrangement; which is achieved by placing the 100 mm and 50 mm wires in a Wheatstone bridge with the 100 mm wire as the sensor and 50 mm wire as a compensation wire. The apparatus requires a 100 ml of test fluid to perform the experiment. The testing temperature of the test fluid during the experimentation can be suitably varied by the choice of heat exchange fluid used in the apparatus. Water is chosen as testing fluids for primary standards. When compared to single wires, the thermal conductivity of the fluids measured is consistent with dual-wire method with an uncertainty of ±0.25%.     

The Elevated Temperature Wear Analysis of Laser Surface–Hardened EN25 Steel Using Response Surface Methodology

The wear behavior of as-received and laser-hardened EN25 low-alloy steel is performed in dry sliding condition using a pin-on-disc-type machine. A response surface methodology–based Box-Behnken design is used to design the experimental matrix by reducing the number of experimental conditions and to develop mathematical models between the key process parameters. The process parameters considered are applied load, temperature, and sliding distance and the responses are wear rate and coefficient of friction. Analysis of variance is used to analyze the developed model. Laser surface–hardened samples exhibit a lower wear rate (0.099 × 10³to 0.490 × 10³mm³/m) and coefficient of friction (0.080 to 0.245 μ) compared to as-received samples.     

Advance Electronic Load Controller for Micro Hydro Power Plant

Most of the MHP （micro hydro power） plants use ELC （electronic load controller） for speed control. Various types of ELC have been developed so far. A dummy ballast load is connected across each phase of generator terminals and ELC controls the power consumed by the ballast load to result in constant speed operation. The ELC developed so far uses thyristor switches in each phase to control ballast load power. The ELC senses the system frequency and comparing it with reference frequency, it generates a common value of firing angle for all three thyristor pairs of each phase. The performance of such ELC is not perfect for unbalanced consumers load connected in each phase, which overloads the generator. This paper presents an advanced type of ELC which senses frequency as well as consumer＇s load current of each phase and fires the thyristor pairs with different value of firing angles for different phases. This solves the problem of overloading of the generator with unbalanced consumer＇s load. Simutink model is developed to perform transient analysis of the proposed scheme and the prototype of hardware is also fabricated. The simulation results and experimental results are presented.     

Experimental and Numerical Investigation of Effusion Cooling Performance Over Combustor Liner Flat Plate Model

ABSTRACT

This article presents a study of cooling performance of combustor liner of a gas turbine, using a flat plate model. The combustion process in gas turbine engines liberates very high temperature gases, which impacts the properties of the combustor liner. Hence, cooling of liner is important and is carried out by effusion cooling method. Experiments are carried out over a flat plate with staggered effusion holes. The hot mainstream air flows at a Reynolds number of 2.325 × 10⁵, which indicates a turbulent flow. The coolant to mainstream density ratios of 1.3 and 1.5 is maintained by varying the blowing ratios ranging from 0.5 to 2.5. Test plate surface temperature measurements are recorded by an infrared camera and the overall cooling effectiveness in the flow direction is calculated. Numerical validation for conjugate heat transfer analysis is performed using ANSYS workbench and the temperature contours obtained are compared with infrared camera images. MATLAB program is used to obtain the effectiveness contours for experimental and computational fluid dynamics results. The effectiveness contours are found to be similar, showing the increase in effectiveness with the increase in blowing ratios. Density ratios comparison shows that with the increase in density ratio, the overall cooling effectiveness marginally decreases.     

Numerical and Experimental Investigations of Heat Removal Performance of Sodium-to-Air Heat Exchanger Used in Fast Reactors

Sodium-to-air heat exchangers (AHX) are used in fast breeder reactors for removal of decay heat generated in the core after a reactor shutdown. The AHX is an important component of the safety-grade decay heat removal system in a fast reactor. Decay heat removal critically depends on the performance of the AHX, which is essentially a cross-flow heat exchanger with liquid sodium flowing on the tube side and air flowing across finned tubes in the cross-flow mode. In this paper, a three-dimensional numerical study is carried out to investigate the flow and heat transfer characteristics when air flows over a representative bank of finned tubes in an AHX. The computational model has been validated against published experimental benchmarks. Based on parametric studies, appropriate correlations for the Nusselt number and fin effectiveness are derived. A computationally efficient porous body model is then developed and an integrated thermal hydraulics study of AHX is carried out using the derived heat transfer correlation. The numerical predictions of the porous body model are compared with the results of an experimental AHX tested at the Indira Gandhi Centre for Atomic Research; Kalpakkam, India. A good agreement between the results is seen.