Faculty Publications
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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 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 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.Item Investigations on boiling-induced nanoparticle coating, transient characteristics, and effect of pressure in pool boiling heat transfer on a 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 (0.0015 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.Item Augmentation of heat transfer coefficient in pool boiling using compound enhancement techniques(Elsevier Ltd, 2017) Sathyabhama, A.; Dinesh, A.Modern compact electronic chip design demands more efficient and innovative cooling techniques in a limited space. One such method is the immersion cooling by pool boiling heat transfer, which is a highly efficient technique when compared with conventional cooling techniques. The boiling heat transfer coefficient can be enhanced using active and passive techniques. In the present investigation grooves as passive and surface vibration as active techniques were coupled to improve the boiling heat transfer coefficient. The forced vertical vibrations were induced on the copper grooved surface with a mechanical vibrator. The frequency of vibration was varied in the range 0–100 Hz and the amplitude of vibration was varied in the range 0–2.5 mm. The compound technique gave 62% improvement in heat transfer coefficient at 300 kW/m2 heat flux compared to the 29% enhancement due to grooves alone and 10% enhancement due to vibration alone. The experimental results were used to develop a modified Rohsenow correlation which predicts the experimental Nusselt number with an accuracy of ±25%. Boiling visualization was performed and the bubble parameters such as bubble departure diameter, bubble frequency and bubble growth were determined. The bubble departure diameter decreased by almost 36% and the bubble frequency increased by 221% for boiling on vibrated grooved surface. © 2017 Elsevier LtdItem Enhancement of Boiling Heat Transfer Using Surface Vibration(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2017) Sathyabhama, A.; Pandiyan, S.P.An experimental investigation of the effect of mechanical vibrations of a copper flat circular surface on the pool boiling heat transfer coefficient of water at atmospheric pressure are presented in this paper. A vibration exciter was used to vibrate this copper test surface vertically. Effect of frequency and amplitude of vibration on the boiling heat transfer coefficient was studied. An increase in the heat transfer coefficient was observed at low frequency and amplitudes, at higher amplitude and frequency heat transfer deteriorates. Heat transfer coefficient increases up to 26% with vibration intensity, represented by vibrational Reynolds number. © 2015 Wiley Periodicals, Inc.Item Flow boiling heat transfer and pressure drop analysis of R134a in a brazed heat exchanger with offset strip fins(Springer Verlag service@springer.de, 2017) Amaranatha Raju, M.; Ashok Babu, T.P.; Chennu, C.The saturated flow boiling heat transfer and friction analysis of R 134a were experimentally analyzed in a brazed plate fin heat exchanger with offset strip fins. Experiments were performed at mass flux range of 50–82 kg/m2 s, heat flux range of 14–22 kW/m2 and quality of 0.32–0.75. The test section consists of three fins, one refrigerant side fin in which the boiling heat transfer was estimated and two water side fins. These three fins are stacked, held together and vacuum brazed to form a plate fin heat exchanger. The refrigerant R134a flowing in middle of the test section was heated using hot water from upper and bottom sides of the test section. The temperature and mass flow rates of water circuit is controlled to get the outlet conditions of refrigerant R134a. Two-phase flow boiling heat transfer and frictional coefficient was estimated based on experimental data for offset strip fin geometry and presented in this paper. The effects of mass flux, heat flux and vapour quality on heat transfer coefficient and pressure drop were investigated. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier ?f, and Martinelli parameter X. © 2017, Springer-Verlag Berlin Heidelberg.Item Investigation of flow boiling heat transfer and pressure drop of R134a in a rectangular channel with wavy fin(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2020) Amaranatha Raju, M.; Ashok Babu, T.P.; Chennu, C.The saturated flow boiling heat transfer and pressure drop studies of R134a were experimentally investigated in a rectangular channel with wavy fin. Experiments were performed at mass flux range 30–50 kg m?2 s?1, heat flux range 11–18 kW m?2 and quality 0.26–0.8. The experimental data were obtained in a brazed test section. In preliminary step, single phase experiments were conducted to find out the j and f data of the wavy fin. In second step, two-phase flow boiling experiments were conducted to estimate the heat transfer and frictional coefficient based on experimental data. The trends of heat transfer and pressure drop with respect to mass flux, heat flux and quality were studied. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier, ?f and Martinelli parameter, X. © 2019 Elsevier Masson SASItem Numerical investigation on subcooled boiling heat transfer coefficient of water-ethanol mixture by CISCAM technique(Korean Society of Mechanical Engineers, 2023) Suhas, S.B.; Mangrulkar, C.K.; Umashankar, K.K.K.; Sathyabhama, S.The subcooled flow boiling (SFB) of a water-ethanol mixture are relevant in operating heat-dissipating devices, such as smaller catalytic reactors, electronic apparatus, and hybrid electric vehicle battery components. The operative temperature should always be at a sustainable value to evade the failure or breakdown of these heat-dissipating devices. To cool these devices, a water-ethanol mixture is used as a coolant. The forced convective as well as SFB heat transfer coefficients (HTCs) for the water-ethanol mixture are estimated numerically using the volume of fluid method in a rectangular channel with dimensions of 15 mm×15 mm×150 mm. During SFB, the liquid-vapor interaction is examined by solving the bubble void fraction (BVF). For the discretization process, the Crank-Nicholson implicit method (scheme) is used, and the convective equation for the BVF is converted to an algebraic equation. The corrector predictor equation procedure is used for solving the BVF. The thermodynamic and thermophysical parameters related to subcooled boiling are estimated upon the incorporation of the bubble void fraction (α) using the mixture rule. These parameters are then incorporated into the x-momentum equation as well as into the energy equation for finding the fluid temperature, velocity, and pressure drop values. From the estimated values of temperature, subcooled flow boiling HTC is obtained. The estimated values of HTC can predict well compared with that of empirical equations. Moreover, mass flux plays a vital role in the forced convective region, while heat flux has a crucial role in the SFB region for the improvement of HTC. © 2023, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.