Faculty Publications
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Item Experimental investigation on boiling heat transfer coefficient enhancement using grooves for cooling of electronic devices(Institute of Electrical and Electronics Engineers Inc., 2014) Sathyabhama, S.; Pandiyan, S.P.This paper presents the experimental investigation of pool boiling heat transfer performance of copper plain and grooved horizontal circular surfaces immersed in saturated water at atmospheric pressure. Effect of geometric parameters of the groove on boiling heat transfer coefficient was studied. Experimental results showed significant increase in boiling heat transfer coefficients at high heat flux with the provision of grooves. An increase in boiling heat transfer was observed with increase in fin thickness and groove depth. © 2014 IEEE.Item Assessment of mixture boiling heat transfer correlations for ammonia/water mixture(2009) Sathyabhama, A.; Ashok Babu, T.P.The aim of this work is to present a critical examination of both the available experimental data and the performance of the available mixture boiling heat transfer correlations for ammonia/water mixture. First, a selection and comparison of the experimental database found in the open literature at the mentioned working conditions is presented. Subsequently, after a short description of the most relevant heat transfer correlations, and in accordance with the selected data, a detailed analysis of the performance of each correlation is carried out. Results show a small divergence between the experimental data sets and conclude that the presently available correlations show considerable discrepancies in heat transfer coefficients within the selected conditions. © 2009 Wiley Periodicals, Inc.Item Critical heat flux enhancement in pool boiling using alumina nanofluids(2010) Hegde, R.N.; Rao, S.S.; Reddy, R.P.The pool boiling characteristics of dilute dispersions of alumina nanoparticles in water were studied. Consistent with other nanofluid studies, it was found that a significant enhancement in critical heat flux (CHF) can be achieved at modest nanoparticle concentrations (<0.1% by volume). During experimentation and subsequent inspection, formation of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly changes surface texture of the heater wire surface which could be the reason for improvement in the CHF value. © 2010 Wiley Periodicals, Inc.Item 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.Item 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.Item 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.Item Nucleate pool boiling heat transfer measurement and flow visualization for ammonia-water mixture(2011) Sathyabhama, A.; Ashok Babu, T.P.Visualization of bubble nucleation during nucleate pool boiling outside a vertical cylindrical heated surface was done for ammonia-water binary mixture in order to obtain a descriptive behavior of the boiling, which was directly compared with the measured heat transfer coefficient data at low pressure of 4-8 bar and at low mass fraction of 0 < x < 0.3 and at different heat flux. Still images taken with high speed camera are used to demonstrate the decrease in boiling heat transfer coefficient with increase in ammonia mass fraction. Jensen and Memmel model has better agreement with experimental bubble diameter. Further work is required to obtain quantitative information about bubble nucleation parameters. It is found that both Calus and Rice and Stephan-Koorner correlation can predict the experimental heat transfer coefficient values with a maximum deviation of ±20%. © 2011 American Society of Mechanical Engineers.Item 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.Item Flow visualization and study of critical heat flux enhancement in pool boiling with Al2O3-water nanofluids(Serbian Society of Heat Transfer Engineers, 2012) Hegde, R.N.; Rao, S.S.; Reddy, R.P.Pool boiling heat transfer characteristics of Al2O3 -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.Item 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.