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Siddaramanna A.,University of Quebec at Chicoutimi | Siddaramanna A.,Vijaya College | Saleema N.,National Research Council Canada | Sarkar D.K.,University of Quebec at Chicoutimi
Applied Surface Science | Year: 2014

Multifunctional superhydrophobic surfaces based on photocatalytic material, ZnO have generated significant research interest from both fundamental and potential applications. Superhydrophobic ZnO surfaces are usually made in multi steps by creating rough surface and subsequent hydrophobization by low-surface-energy materials. Herein, a simple and one step chemical bath deposition has been developed to prepare superhydrophobic ZnO surfaces on aluminum substrate. The aluminum surfaces covered with randomly distributed ZnO particles can not only present multiscale surface roughness, but also readily coordinate with fatty acid, leading to special wettability. The contact angle of the resulting superhydrophobic surface reaches up to 165 ± 2° and contact angle hysteresis of 4°. The contact angle and contact angle hysteresis variation as a function of particle size has been discussed systematically based on surface morphology. © 2014 Elsevier B.V. Source

Shivakumara I.S.,Bangalore University | Ng C.-O.,University of Hong Kong | Nagashree M.S.,Vijaya College
International Journal of Engineering Science | Year: 2011

The criterion for the onset of electrothermoconvection in a rotating horizontal layer of Brinkman porous medium is investigated for different types of velocity boundary conditions namely, (i) both boundaries stress-free, (ii) both boundaries rigid and (iii) lower rigid and upper free boundaries. Results indicate that the nature of boundaries and speed of rotation significantly influence the stability characteristics of the system. In the case of stress-free condition, it is shown that the necessary conditions for the occurrence of oscillatory onset are independent of an external electric field. Contrary to their stabilizing effect in the absence of rotation, increasing the ratio of viscosities Λ and decreasing the Darcy number Da show some destabilizing effect on the onset of stationary electrothermoconvection in the presence of rotation and some important observations are made on the stability characteristics of the system. Moreover, the similarities and differences between free-free, rigid-rigid and rigid-free boundaries are emphasized in triggering the onset of electrothermoconvection in a rotating porous layer. For small Taylor number domain, the stress-free boundaries is found to be always unstable than that of rigid-rigid and rigid-free boundaries. However, this trend is reversed at higher Taylor number domain because the stability of the stress-free case is increased more quickly than the other boundaries. © 2011 Elsevier Ltd. All rights reserved. Source

Nagaraju P.,Vijaya College
Special Topics and Reviews in Porous Media | Year: 2015

The effects of variable porosity and thermal conductivity of a medium, and also the emission, absorption, and scattering of radiation, are studied in this paper. A comparative study has been made for three different situations, namely, (1) variable porosity; (2) constant porosity; and (3) absence of porous medium. In carrying out the solution, as a first step the temperature profile within the radiation layer is determined and hence the heat transfer in the presence as well as in the absence of radiation parameter is obtained. The momentum and energy equations are coupled and they are solved simultaneously by the Runge-Kutta-Gill method in conjunction with the Newton-Raphson iterative scheme. The results of the analyses show that in the cases of variable porosity and absence of porous medium the velocity profiles possess very small curvature at the wall, whereas in the case of the constant porosity situation the velocity profile is almost zero up to a certain distance and then increases. Nevertheless, it reaches unity asymptotically in all three cases. The temperature profile becomes linear as the value of the ratio of the thermal conductivity of a solid to a fluid, λs/λf increases. Another important result of the analyses is that the rise in temperature in a variable porosity medium is about 25% more in comparison with the absence of porous medium. Furthermore, the results show that the total heat flux in a variable porosity medium is about 79% more compared to a constant porosity medium, and the variable conductivity enhances the total heat flux by about 33% compared to the constant conductivity of the medium. The results also show that as the radiation parameter increases the total heat flux decreases in all three cases. © 2015 by Begell House, Inc. Source

Nethravathi B.P.,Vijaya College | Ramakrishna Reddy K.,Government Science College | Mahendra K.N.,Bangalore University
Journal of Porous Materials | Year: 2014

Cobalt(II), copper(II) and zinc(II) complexes of 2-phenylbenzimidazole (PhBzlH) encapsulated in the supercages of zeolite-Y and ZSM-5 have been synthesized and characterized by spectroscopic studies (IR, UV/visible, EPR), elemental analyses, thermal studies and X-ray diffraction patterns. The catalytic activity of encapsulated complexes was investigated for the hydroxylation of phenol using 30 % H2O2 as an oxidant. Under optimized reaction conditions, the hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. A maximum conversion of phenol was obtained with [Cu(PhBzlH)]-Y as the catalyst. The results showed that conversion of phenol varies in the order [Cu(PhBzlH)]-Y (53 %) > [Cu(PhBzlH)]-ZSM-5 > (49 %) > [Co(PhBzlH)]-ZSM-5 (47 %) > [Co(PhBzlH)]-Y (46 %) > [Zn(PhBzlH)]-Y (45 %) > [Zn(PhBzlH)]-ZSM-5 (41 %) after 6 h of reaction time. Test for the recyclability of the reaction was also carried out and the results indicate their recyclability. © 2014 Springer Science+Business Media New York. Source

Govind A.S.,Vijaya College | Suresha B.L.,Bangalore University | Radhakrishna M.C.,Bangalore University
Liquid Crystals | Year: 2012

The response of liquid crystals to light is very important in applications of liquid crystals in display and memory devices. Experiments have been conducted on liquid crystals doped with photoactive azo compounds, and has been shown that under incident UV radiation such systems can lower the nematic isotropic transition temperature, T NI. In addition, in some mixtures a photo-induced smectic phase is observed, attributable to the change from the trans (longer) isomer to the cis (shorter) isomer in the photoactive dopant. We have previously developed a molecular mean field model, on the assumption that the medium consists of interconverting anti-parallel and parallel pairs, to explain the molecular origin of 'two lengths'. The model was used to explain double re-entrance, the effect of electric field on T NI, etc. This model has now been modified to include the change between the trans and cis isomer, which is equivalent to an increase in the fraction of parallel (shorter) pairs. The phase diagram calculated for incident UV radiation energy shows an induced smectic phase. This is in qualitative agreement with the experimental trends. © 2012 Copyright Taylor and Francis Group, LLC. Source

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