Journal Articles
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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 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 Effect of surface vibration on boiling heat transfer froma copper flat circular disc(Begell House Inc. orders@begellhouse.com, 2016) Sathyabhama, A.; Pandiyan, P.S.This paper presents the experimental investigation of the effect of surface vibration on pool boiling heat transfer from a copper flat circular surface immersed in saturated water at atmospheric pressure. The forced vertical vibrations were induced on this copper test surface with the help of a mechanical vibrator. The frequency was varied in the range 0-25 Hz and the amplitude of vibration was varied in the range 0-5 mm. The results indicate that the heat transfer coefficient increases at low frequency and amplitudes; at higher amplitude and frequency, heat transfer deteriorates in the investigated range. Rohsenow-type correlation was developed, which predicts the present experimental data with an average absolute error of 30%. © 2018 by Begell House, Inc.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 Transient CHF enhancement in high pressure pool boiling on rough surface(Elsevier B.V., 2018) Walunj, A.; Sathyabhama, A.Experimental investigation of transient pool boiling heat transfer (PBHT) to saturated water from thick, non-lumped 20 mm diameter copper sample is carried at 1 bar, 5 bar and 10 bar pressure. The time constant (?) of exponential heat supply is varied from 1 to 6. The unidirectional scratches are made on the surface to obtain wide range of surface roughness varying from Ra = 0.106 ?m to Ra = 4.03 ?m. The effect of surface roughness, pressure and time constant on transient critical heat flux (CHF) is extensively studied. Transient CHF enhancement for Ra = 4.03 ?m when ? = 1 is found to be 98.88%, 76.55% and 53.21% at pressures P = 1 bar, P = 5 bar and P = 10 bar, respectively, however it is found to be lower by 9.38%, 21.40% and 9.73%, compared to steady state CHF enhancement for Ra = 4.03 ?m, at respective pressures. The Gorenflo correlation is modified by including the additional parameter ? and it predicts the present transient HTC values with mean absolute error (MAE) of 14.91%. The CHF model is developed by considering the effect of capillary wicking in the narrow unidirectional scratches and the bubble angle. This model predicts the present transient CHF values with MAE of 11.89%. © 2018 Elsevier B.V.Item Boiling of saturated water on grooved surface(Serbian Society of Heat Transfer Engineers, 2019) Sathyabhama, A.The flow patterns and pool boiling heat transfer performance of rectangular grooved surface immersed in saturated water were experimentally investigated. The effect of the aspect ratio (groove depth/fin thickness) on boiling performance was examined. The test surfaces were manufactured on a copper block with a base diameter of 19 mm with four fin thickness (0.5 mm, 1mm, 1.5 mm and 2 mm) and three groove depths (1.0 mm, 2.0 mm and 3.0 mm). All experiments were performed in the saturated state at atmospheric pressure. A plain surface was used as the reference standard and compared with the grooved surfaces. The photographic images showed different boiling flow patterns among the test surfaces at various heat fluxes. The test results indicated that closer and more number of grooves yielded a greater flow resistance against the bubble/vapor lift-off along the groove wall. At higher heat flux, numerous vapor mushrooms periodically appeared from the perimeter of the grooves. The developed correlation for Nusselt number predicts the experimental data with MAE of 7.42%. © 2018 Serbian Society of Heat Transfer Engineers.Item Experimental investigation on transient pool boiling heat transfer from rough surface and heat transfer correlations(International Information and Engineering Technology Association info@iieta.org, 2019) Walunj, A.; Sathyabhama, A.This paper presents the study of transient boiling characteristics on rough copper sample with surface roughness value (Ra) ranging from 0.106 ?m to 4.03 ?m. The effect of roughness and time constant of exponential heat supply on transient critical heat flux (CHF), maximum heat transfer coefficient (HTC) and onset of nucleate boiling (ONB) is extensively studied. The mechanism of heat transfer in unidirectional scratches of rough sample is discussed. High speed visualization is carried to observe the stages of boiling and bubble dynamics. The HTC correlation developed in this study predicts the present experimental values of HTC with a mean absolute error (MAE) of 9.62 %. © 2019 International Information and Engineering Technology Association. All rights reserved.