Fluid properties of an unsteady MHD free stream flow over a stretching sheet in presence of radiation

Variable fluid properties with thermal radiation in an unsteady magnetohydrodynamics free stream incompressible flow over a stretching sheet has been considered. The thermal diffusivity and viscosity of the fluid varies linearly with temperature. The governing partial differential equations are moulded to ordinary differential equations using time-dependent similarity variables and the stream function. RKF technique with shooting method has been implement to find the solution numerically. In the current analysis the impact of unsteadiness, magnetic field, radiative parameter, variable fluid viscosity and thermal diffusivity parameter on heat and flow behavior with the free stream parameter have been studied. Transition point observed in the velocity profiles with an change in unsteadiness parameter and the effect of magnetic field is reduced in the presence of free stram velocity. The velocity and the temperature gradient are computed on the surface and their outcomes with different parameters have been analyzed in the results shown graphically and in tabular form.     

Mechanical and gas permeation properties of compatibilized polypropylene–layered silicate nanocomposites

Nanocomposites of polypropylene with montmorillonite modified with dimethyldioctadecylammonium ions were prepared and the effect of compatibilizers on the mechanical and permeation properties was investigated. Compatibilizers were selected on the basis of their chemical nature, molecular weight, amount of grafting and location of the polar groups. Addition of small amount of compatibilizers led to improvements in the basal spacings of clay platelets indicating enhanced exfoliation. The modulus of the composites increased as compared with the values without compatibilizer. The oxygen permeation through the composite films either increased or remained unaffected due to possible interfacial free volume enhancement owing to the incompatibility of the surface modification and the compatibilizer. Increasing the amount of compatibilizer also increased correspondingly the extent of exfoliation. The modulus reached a plateau value after which the increasing compatibilizer led to its decrease. The gas permeation through the composite films remained unchanged with increase in the amount of compatibilizer owing to a possible balance between the decrease in permeation due to path tortuity and exfoliation and increase in permeation due to interfacial incompatibility. The improving exfoliation improved the yield and break stress indicating that the absence of tactoids can hinder the premature failure owing to better stress transfer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of High-Temperature Severe Plastic Deformation on Microstructure and Mechanical Properties of IF Steel

Extensive research work has been carried out on interstitial-free steel to understand its response to deformation; particularly, the behavior during severe plastic deformation (SPD). However, most of these studies were mainly undertaken in the ferritic regime. The present investigation reports the initial results of our attempt to employ accumulative roll bonding (ARB), one of the variants of SPD, at a high temperature (950 °C). A considerable grain refinement has been observed, which may be attributed to the severity of deformation and recrystallisation at high temperatures. Nanoindentation tests have been performed at various stages of ARB process to understand the evolution of mechanical properties.     

Performance analysis of earth-pipe-air heat exchanger for summer cooling

Earth-pipe-air heat exchanger (EPAHE) systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth-air-pipe heat exchanger systems. The model was developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth-air-pipe heat exchanger systems are studied. The 23.42 m long EPAHE system discussed in this paper gives cooling in the range of 8.0-12.7 °C for the flow velocities 2-5 m/s. Investigations on steel and PVC pipes have shown that the performance of the EPAHE system is not significantly affected by the material of the buried pipe (pipe). Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. The COP of the EPAHE system discussed in this paper varies from 1.9 to 2.9 for increase in velocity from 2.0 to 5.0 m/s.     

Physico-chemical,mechanical and electrical performance of bael fruit gum–chitosan IPN films

The gum obtained from unripe fruits of Aegle marmelos was co-processed with chitosan to improve the film forming property of the former. The results of FTIR and differential thermal analysis of films revealed maximum interaction between –COO⁻ groups of gum and –NH₃⁺ of chitosan when they were present in equal proportion in the film. These films exhibited almost negligible zeta potential and the surface remained smooth after exposure to both acidic and alkaline pH as observed under scanning electron microscope. The contact angle and swelling index of this film in both acidic and alkaline buffers were observed to be lowest as compared to other films prepared with different ratios of gum and chitosan. The work of adhesion and spreading coefficient for this film was observed to be lowest. These results could be attributed to optimum interaction between –COO⁻ groups of gum and –NH₃⁺ groups of chitosan. These results indicated the ability of this film for use in modifying drug release and processed food items.     

Fatigue Crack Growth Behaviour of Conventional and Modified IN 718 Superalloys at 650 °C

In the present investigation, the fatigue crack growth behaviour of modified IN 718 superalloy (Ni-0.02 %, C-19.04 %, Cr-19.31 %, Fe-3.04 %, Mo-4.73 %, Nb-1.01 %, Al-1.16 %, Ti-0.0033 %, B, all in wt%) has been compared with conventional IN 718 superalloy (Ni-0.02 %, C-19.0 %, Cr-19.35 %, Fe-3.0 %, Mo-5.10 %, Nb-0.50 %, Al-1.00 %, Ti-0.0033 %, B, all in wt%) at 650 °C. Modified IN 718 superalloy exhibits marginally lower crack growth rate as compared to conventional alloy and was attributed to roughness induced crack closure.     

A reconfigurable microstrip cross parasitic antenna with complete azimuthal beam scanning and tunable beamwidth

In this article, a reconfigurable cross parasitic antenna is proposed to achieve complete azimuthal beam scanning and tunable beamwidth in the E‐ and H‐plane. The antenna consists of a square‐shaped driven element and four size‐tunable parasitic elements placed on each side of the driven element. Each tunable parasitic element is composed of a hexagonal slot loaded with two varactor diodes. The tunable parasitic element shows dual‐resonance behavior and hence its effective electrical size can be controlled with respect to the driven element. The radiated beam of the cross antenna is continuously scanned in the elevation plane from θ = 0° to 10.8°, 0° to 32.4°, and 0° to 40° in ? = (0°, 180°), (45°, 135°, 225°, 315°), and (90°, 270°) planes, respectively. Moreover, the 3‐dB beamwidth of the cross antenna is continuously tuned from 65° to 152° and from 64° to 116° in the E‐ and H‐plane, respectively. The antenna shows good impedance matching in all the operating modes with ?10 dB bandwidth from 2.43 to 2.47 GHz. A prototype of the antenna is fabricated to experimentally verify the simulated reflection and radiation characteristics.