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Yelahanka, India

Hegde R.N.,M.S. Ramaiah Institute of Technology | Rao S.S.,Indian National Institute of Engineering | Reddy R.P.,Reva Institute of Technology
Experimental Heat Transfer | Year: 2012

Pool boiling experiments were conducted to study the heat transfer characteristics using low concentrations (0.0015 to 0.0077 vol%) of CuO nanofluids at and above atmospheric pressure in distilled water. The study included the following. (i) effect of pressure and concentration on heat transfer using CuO nanoparticles in distilled water, (ii) investigations on nanoparticle coating formed due to boiling-induced precipitation tested in CuO nanofluid and distilled water, and (iii) pool boiling behavior of CuO nanofluid subject to transient characteristics. The experimental outcome indicated that different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer coefficients at and above atmospheric pressure. Boiling-induced precipitation of nanoparticles resulted in coating of nanoparticles. When tested in pure water, the nanoparticle-coated heater showed significant increase in critical heat flux compared with the critical heat flux of a bare heater tested in pure water. Study of the transient characteristics indicated degradation in boiling heat transfer due to prolonged exposure of the heater surface in nanofluid. Based on the experimental investigations, it can be concluded that nanoparticle coating can also be a potential substitute for enhancing the heat transfer if used in controlled quantities. © 2012 Taylor & Francis Group, LLC. Source


Hegde N.R.,M.S. Ramaiah Institute of Technology | Rao S.S.,Indian National Institute of Engineering | Reddy R.,Reva Institute of Technology
Thermal Science | Year: 2012

Pool boiling heat transfer characteristics of Al 2O 3 -water nanofluids is studied experimentally using a NiCr test wire of 36 standard wire guage diameter. The experimental work mainly concentrated on (1) change of critical heat flux with different volume concentrations of nanofluid and (2) flow visualization of pool boiling using a fixed concentration of nanofluid at different heat flux values. The experimental work revealed an increase in critical heat flux value of around 48% andflow visualization helped in studying the pool boiling behaviour of nanofluid.Out of the various reasons which could affect the critical heatflux enhancement, surface roughness plays a major role in pool boiling heat transfer. Source


Kapilan N.,National Institute of Technology Karnataka | Ashok Babu T.P.,National Institute of Technology Karnataka | Reddy R.P.,Reva Institute of Technology
ASTM Special Technical Publication | Year: 2011

Fuel crisis because of dramatic increase in vehicular population and environmental concerns have renewed the interest of the scientific community to look for alternative fuels of bio-origin such as vegetable oils and ethanol. India is looking at biodiesel derived from Mahua oil (MO), as one of the renewable alternative fuels for compression ignition (CI) engine. Although MO biodiesel (MOB) has several advantages over fossil diesel, in the present scenario, the use of biodiesel is restricted due to its high cost. In India, liquefied petroleum gas (LPG) is easily available and is one of the cheapest gaseous fuels. Hence, use of LPG to fuel a CI engine along with MOB seems to be an option for substitution of fossil diesel. In the present work, LPG, which was fumigated along with the air and biodiesel was admitted into the engine cylinder through conventional fueling device as an igniter. A single cylinder CI engine was modified to work in dual fuel mode and engine tests were carried out at rated speed under variable load conditions. The performance of the engine in dual fuel mode was compared with the diesel. The dual fuel operation results in thermal efficiency close to the diesel and also reduces the NOx and smoke emissions significantly. From the experimental results, we concluded that biodiesel in dual fuel mode with cheaper gaseous fuel induction is an option for reducing the operating cost of the biodiesel fuelled CI engine. Copyright ©2011 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Source


Hegde R.N.,M.S. Ramaiah Institute of Technology | Reddy R.P.,Reva Institute of Technology | Rao S.S.,Indian National Institute of Engineering
Heat Transfer - Asian Research | Year: 2011

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. Source


Hegde R.N.,National Institute of Technology Karnataka | Rao S.S.,Indian National Institute of Engineering | Reddy R.P.,Reva Institute of Technology
Experimental Thermal and Fluid Science | Year: 2012

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. Source

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