Faculty Publications

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Publications by NITK Faculty

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    Criticality of charged ads black hole with a global monopole
    (Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Naveena Kumar, A.; Ahmed Rizwan, C.L.A.; Ajith, K.M.
    We discuss the phase transition of charged AdS black hole surrounded by a global monopole. The cosmological constant is taken as fluid pressure and the corresponding conjugate variable as volume. In this extended phase space, the criticality is investigated from P-V isotherms, Gibbs free energy behavior and coexistence curves. The critical behavior of the Black Hole is analogous to classical van der Waals gas. This is further verified by looking at the critical exponents. The magnetic monopole parameter affects the phase structure of the black hole significantly. © Springer Nature Singapore Pte Ltd 2020.
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    The Role of Global Monopole in Joule–Thomson Effect of AdS Black Hole
    (Springer Science and Business Media Deutschland GmbH, 2021) Naveena Kumara, A.; Ahmed Rizwan, C.L.; Ajith, K.M.
    We study the throttling process of the AdS black hole with a global monopole in the extended phase space. In the approach followed, the cosmological constant and the black hole mass are identified with the thermodynamic pressure and enthalpy, respectively. We investigate the dependency of the inversion temperature and isenthalpic curves on the global monopole parameter η. Our study shows a close resemblance between the phase transition of the black hole in the extended phase space and Van der Waals fluid. The presence of global monopole plays an important role in the throttling process. © 2021, Springer Nature Singapore Pte Ltd.
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    Cu-44Ni-5Cr alloy has been subjected to thermomechanical treatment which consisted of plastic deformation of as-quenched material by 50, 65 and 80% reduction in thickness followed by ageing in the interval of 500 to 650 °C for various durations of time. Progress in age-hardening was studied by means of hardness measurement and X-ray diffraction studies. The wavelength of composition modulation and strain amplitude were measured. It was found that age-hardening was a result of interaction between spinodal decomposition and recovery processes. Prior deformation was found to enhance the kinetics of both spinodal decomposition and coarsening. It was concluded that this resulted from increased vacancy concentration and increased coherency strain in the cold-worked material. © 1994 Chapman & Hall.
    (Kluwer Academic Publishers, Effect of thermomechanical treatment on the phase transformation in Cu-44Ni-5Cr alloy) Raghavendra Bhat, R.; Prasad Rao, P.
    1994
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    Phase transformation, structural evolution, and mechanical property of nanostructured feal as a result of mechanical alloying
    (Springer New York LLC barbara.b.bertram@gsk.com, 2009) Rajath Hegde, M.M.R.; Surendranathan, A.O.
    The objective of the work is to synthesize nanostructured FeAl alloy powder by mechanical alloying (MEA). The work concentrates on the synthesis, characterization, and structural and mechanical properties of the alloy. Nanostructured FeAl intermetallics are prepared directly by MEA in a high-energy ball mill. Milling is performed under toluene solution to avoid contamination from the milling media and atmosphere. Mixtures of elemental Fe and Al are progressively transformed into a partially disordered solid solution with an average composition of Fe-50 at.% Al. Phase transformation, structural changes, morphology, particle size measurement, and chemical composition during MEA are investigated by X ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). Vickers microhardness (VMH) indentation tests are performed on the powders. The XRD and SEM studies reveal the alloying of elemental powders as well as transition to nanostructured alloy; crystallite size of 18 nm is obtained after 28 h of milling. Expansion/contraction in lattice parameter accompanied by reduction in crystallite size occurs during transition to nanostructured alloy. Longer milling introduces ordering in the alloyed powders as proved by the presence of superlattice reflection. Elemental and alloyed phases coexist while hardness increases during MEA. copy2009 Springer Science+Business Media, Inc.
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    Role of surface roughness in pool boiling with Alumina-water nanofluid on a horizontal wire surface
    (International Information and Engineering Technology Association, 2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
    Boiling heat transfer is one of the major phenomenon which of late, has drawn the attention of many researchers and scientists throughout the world. With nanofluids, further boost is given in heat transfer enhancement. This research paper is the study of heat transfer enhancement using Alumina nanofluid in different volume concentrations ranging from 1 to 9%. The role of surface roughness on critical heat flux enhancement (CHF) in pool boiling with nanofluids was experimentally studied using a 36 gauge NiCr wire at atmospheric pressure. Experimentation included i) investigations on boiling heat transfer subjecting the wire surface to Alumina nanofluid at higher volume concentrations and ii) investigations on surface roughness due to surface coating, subjecting the wire surface to a single heating cycle with different volume concentrations of Alumina nanofluid. Boiling of nanofluid resulted in nanoparticle deposition and subsequent roughning of the wire surface. To substantiate the nanoparticle deposition and its effect on critical heat flux, investigation was done by studying the surface roughness and SEM images of the wire surface. The experimental results show the evidence of nanoparticle deposition on the wire surface and its effect on CHF enhancement and deterioration in pool boiling heat transfer.
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    Experimental investigation in pool boiling heat transfer of ammonia/water mixture and heat transfer correlations
    (2011) Sathyabhama, A.; Ashok Babu, T.P.A.
    The nucleate pool boiling heat transfer coefficient of ammonia/water mixture was investigated on a cylindrical heated surface at low pressure of 4-8bar and at low mass fraction of 0NH3<0.3 and at different heat flux. The effect of mass fraction, heat flux and pressure on boiling heat transfer coefficient was studied. The results indicate that the heat transfer coefficient in the mixture decreases with increase in ammonia mass fraction, increases with increase in heat flux and pressure in the investigated range. The measured heat transfer coefficient was compared with existing correlations. The experimental data were predicted with an accuracy of ±20% by the correlation of Calus&Rice, correlation of Stephan-Koorner and Inoue-Monde correlation for ammonia/water mixture in the investigated range of low ammonia mass fraction. The empirical constant of the first two correlations is modified by fitting the correlation to the present experimental data. The modified Calus&Rice correlation predicts the present experimental data with an accuracy of ±18% and the modified Stephan-Koorner correlation with an accuracy of ±16%. © 2011 Elsevier Inc.
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    Behavioral study of alumina nanoparticles in pool boiling heat transfer on a vertical surface
    (2011) Hegde, R.N.; Reddy, R.P.; Rao, S.S.
    Experiments were carried out to investigate the pool boiling of alumina-water nanofluid at 0.1 g/l to 0.5 g/l of distilled water, and the nucleate pool boiling heat transfer of pure water and nanofluid at different mass concentrations were compared at and above the atmospheric pressure. At atmospheric pressure, different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer. The effect of pressure and concentration of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. The heat transfer coefficient of 0.5 g/l alumina-water nanofluid was compared with pure water and clearly indicates deterioration. At all pressures the heat transfer coefficients of the nanofluid were lower than those of pure water. Experimental observation revealed particles coating over the heater surface and subsequent SEM inspection of the heater surface showed nanoparticles coating on the surface forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, investigation was done by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, surface roughness of the heater surface confirmed it. Based on the experimental investigations it can be concluded that an optimum thickness of nanoparticles coating favors an increase in heat flux. Higher surface temperature due to the presence of nanoparticles coating results in the deterioration of boiling heat transfer. © 2011 Wiley Periodicals, Inc.
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    Experimental study on CuO nanoparticles in distilled water and its effect on heat transfer on a vertical surface
    (2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
    The pool boiling characteristics of dilute dispersions of CuO nanoparticles in water were studied at atmospheric pressure on a vertical heating surface. Experimental investigation of different weight concentrations of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. Out of many reasons, nanoparticles coating the heater surface was believed to be the reason behind this. Subsequent inspection of the heater surface showed nanoparticles coating the surface, forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, an investigation was performed by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, measurement of surface roughness of the heater surface confirmed it. Formation of the porous layer on the heater surface as revealed by SEM images provided an excellent location for nucleation sites enhancing heat transfer. However, deterioration in nucleate boiling at different weight concentrations indicated some phenomenon is working behind this. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
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    Experimental investigation of pool boiling heat transfer in ammonia-water-lithium nitrate solution
    (2012) Sathyabhama, A.; Ashok Babu, T.P.
    The nucleate pool boiling heat transfer coefficient of an NH 3-H 2O-LiNO 3 mixture was investigated on a cylindrical heated surface at low pressure of 4 to 8 bar, low ammonia mass fraction of 0 < xNH 3 < 0.3, and different heat fluxes. The lithium nitrate concentration of the solution was chosen in the range of 10-50% of mass ratio of lithium nitrate in pure water. The effects of concentrations, heat flux, and pressure on boiling heat transfer coefficient was studied. The results indicate that the heat transfer coefficient in the mixture decreases with increase in ammonia mass fraction, increases with the addition of lithium nitrate, and increases with an increase in heat flux and pressure in the investigated range. © 2012 Copyright Taylor and Francis Group, LLC.
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    Studies on nanoparticle coating due to boiling induced precipitation and its effect on heat transfer enhancement on a vertical cylindrical surface
    (2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.
    Pool boiling experiments were conducted to study the heat transfer characteristics using low concentrations (0.1-0.5. g/l) of Alumina-nanofluid at atmospheric pressure in distilled water. The study involved investigation on the effect of nanoparticle coating on the vertical test surface exposed to multiple heating cycles, heat transfer characteristics of nanoparticle coated surface in distilled water and pool boiling behavior of Alumina nanofluid subjected to transient characteristics. In order to quantify the result, surface roughness of the cylindrical surface was measured at different concentrations of nanofluid before and after the experiments. At atmospheric pressure, different concentrations of nanofluids displayed different degrees of deterioration in boiling heat transfer. Coating of nanoparticles was observed on the heater surface due to boiling induced precipitation. The nanoparticle coated heater when tested in pure water showed significant increase in CHF comparable to CHF of bare heater tested in pure water. Study on transient characteristics of the nanofluid, keeping the heat flux constant for a specified time interval showed degradation in boiling heat transfer. The longer the duration of exposure of the heater surface, the higher was the degradation in heat transfer. Based on the experimental investigations it can be concluded that nanoparticle coating can be a potential substitute for enhancing the heat transfer. © 2011 Elsevier Inc.