Faculty Publications
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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 Numerical Analyses of Single-Phase Pressure Drop and Forced Convective Heat Transfer Coefficient of Water–Ethanol Mixture: An Application in Cooling of HEV Battery Module(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2016) Suhas, B.G.; Sathyabhama, A.The present numerical analyses are related to the cooling of a hybrid electric vehicle (HEV) battery module by water–ethanol mixture. The fluid is passed through a cold plate consisting of two rectangular channels of 0.01 m depth, 0.015 m width, and 0.15 m length. The battery module is represented by a heater placed below the cold plate. The single-phase pressure drop and single-phase heat transfer coefficient for water, water–ethanol mixture of mass fraction of 25%, 50%, and 75%, and ethanol are determined numerically for different heat fluxes of 10, 15, 20, and 25 kW/m2 and different Reynolds numbers 500, 1000, 1500, 2000, and 2500. To solve the Navier–Stokes equation, the pressure correction method was used and to solve the energy equation, the Lax–Wendroff explicit method is used. Numerical results obtained for water are compared with the literature correlations. The friction factor for water deviated by an average of 8.02% from the Lewis and Robertson equation. The Nusselt number for water deviated by 7.35% from the Churchill and Ozoe equation at lower Reynolds number 500 and at higher Reynolds number 2500, Nusselt number deviated by 13.68% from the Stephan equation. The results showed that the heat transfer coefficient increased with an increase in Reynolds number and heat flux. The effect of the increase in Reynolds number is more significant than the increase in heat flux. At higher ethanol mass fraction and higher Reynolds number the heat transfer coefficient increased with heat flux when compared to water. There is no significant decrease in heat transfer coefficient with an increase in ethanol mass fraction. The pressure drop increased and the heat transfer coefficient decreased with an increase in ethanol mass fraction. © 2015 Wiley Periodicals, Inc.Item Effect of boiling surface vibration on heat transfer(Springer Verlag service@springer.de, 2017) Sathyabhama, A.Experimental investigation of effect of forced vertical surface vibration on nucleate pool boiling heat transfer of saturated water at atmospheric pressure is presented in this paper. Vertical vibration was induced externally to the circular copper test surface on which boiling took place, using a vibration exciter. Frequency was varied in the range 0–25 Hz and amplitude of vibration was varied in the range 0–5 mm. Boiling takes place at much lower superheats for the same heat flux, slope of boiling curve decreases remarkably, when the surface is given external excitation. High frequency and high amplitude oscillations lead to more intensive heat transfer. There are some combinations of frequency and vibration amplitude, which cause up to two times increase in heat transfer coefficients. © 2016, Springer-Verlag Berlin Heidelberg.Item Comparative study of pool boiling heat transfer from various microchannel geometries(Elsevier Ltd, 2018) Walunj, A.; Sathyabhama, A.This paper presents the experimental investigation of pool boiling heat transfer enhancemrent using open microchannels. Rectangular, parabolic and stepped microchannels are fabricated on the 10 mm diameter circular copper test piece and their boiling characteristics are compared with that of the plain surface at saturated condition of distilled water. The effect of channel shape and geometrical parameter on the boiling heat transfer is studied. The channel top width and channel base width are varied from 250 ?m to 500 ?m and 500 ?m to 800 ?m, respectively. The fin tip thickness is varied from 200 ?m to 500 ?m. The channel height is fixed at 500 ?m. The morphology of bubble is observed by using high-speed camera. Compound study of bubble departure diameter and bubble frequency has proved the significant performance of parabolic and stepped microchannel. All the microchannel geometries enhanced the heat transfer rate. The modification of rectangular channel into parabolic and stepped microchannel resulted in the maximum of 88% and 169% enhancement, respectively at 11.7 °C wall superheat. At heat flux of 100 kW/m2, the heat transfer coefficient increased by 21.49–35.37% for different microchannels. The incipient temperature reduced by 13.72–23.18%. A semi-analytical model is developed to estimate the bubble departure diameter of the microchannel which predicts the present experimental data with mean absolute error of 5.58%. © 2017 Elsevier LtdItem Heat transfer and force balance approaches in bubble dynamic study during subcooled flow boiling of water–ethanol mixture(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2018) Suhas, B.G.; Sathyabhama, A.In this paper, the subcooled flow boiling heat transfer coefficient of pure water, water–ethanol mixture and pure ethanol is determined experimentally in horizontal rectangular channels for various parameters like heat flux, mass flux and channel inlet temperatures. Flow visualization is carried out using high speed camera. The bubble departure diameter, growth period and waiting period of bubbles are determined. Correlations are developed for subcooled flow boiling Nusselt number of water–ethanol mixture based on force balance approach and heat transfer approach. The parameters considered for correlation are grouped as dimensionless numbers by Buckingham ?-theorem. The significance of each dimensionless number on heat transfer coefficient is discussed. The correlations developed for subcooled flow boiling heat transfer coefficient are validated with the experimental data. They are found to be in good agreement with the experimental data. It is found that the correlation based on force balance approach predicts the subcooled flow boiling Nusselt number well when compared with that of heat transfer approach correlation. © 2017 Taylor & Francis.Item Experimental study on forced convective and subcooled flow boiling heat transfer coefficient of water-ethanol mixtures: an application in cooling of heat dissipative devices(Springer Verlag service@springer.de, 2018) Suhas, B.G.; Sathyabhama, A.The experimental study is carried out to determine forced convective and subcooled flow boiling heat transfer coefficient in conventional rectangular channels. The fluid is passed through rectangular channels of 0.01 m depth, 0.01 m width, and 0.15 m length. The parameters varied are heat flux, mass flux, inlet temperature and volume fraction of ethanol. Forced convective heat transfer coefficient increases with increase in heat flux and mass flux, but effect of mass flux is less significant. Subcooled flow boiling heat transfer increases with increase in heat flux and mass flux, but the effect of heat flux is dominant. During the subcooled flow boiling region, the effect of mass flux will not influence the heat transfer. The strong Marangoni effect will increase the heat transfer coeffient for mixture with 25% ethanol volume fraction. The results obtained for subcooled flow boiling heat transfer coefficient of water are compared with available literature correlations. It is found that Liu-Winterton equation predicts the experimental results better when compared with that of other literature correlations. An empirical correlation for subcooled flow boiling heat transfer coefficient as a function of mixture wall super heat, mass flux, volume fractions and inlet temperature is developed from the experimental results. © 2017, Springer-Verlag GmbH Germany.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 Bubble dynamics and enhanced heat transfer during high-pressure pool boiling on rough surface(American Institute of Aeronautics and Astronautics Inc. custserv@aiaa.org, 2019) Walunj, A.; Sathyabhama, A.In the present study, the influence of surface roughness (Ra) on critical heat flux (CHF) of water at pressure of 1, 5, and 10 bar is investigated. The desired value of Ra is achieved by making unidirectional scratches on the flat copper surface. Surface roughness Ra varies from 0.106 to 4.03 ?m. The high-speed camera of 1000 fps is used for the boiling visualization study. The effect of surface roughness on bubble departure diameter and bubble frequency at different pressure is reported. Kim's CHF model is modified to include the contact angle as a function of surface roughness and temperature, which predicts the experimental CHF with mean absolute error (MAE) of 10.50% at pressure up to 10 bar. The correlation developed for bubble departure diameter predicts the experimental values with MAE of 17.09%. The relation between bubble departure diameter and bubble frequency is also developed, which predicts the corresponding experimental values with MAE of 25.26%. © 2019 American Institute of Aeronautics and Astronautics Inc. All rights reserved.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.Item Experimental and numerical investigation of pool boiling heat transfer from finned surfaces(Elsevier Ltd, 2023) Jaswal, R.; Sathyabhama, A.; Singh, K.; Yandapalli, A.V.V.R.P.An experimental study of the pool boiling process on three test surfaces, namely, Plain surface, Rectangular finned surface, and Trapezoidal finned surface, was carried out using distilled water as the working fluid at atmospheric pressure. A parametric study of finned surfaces was performed to understand the effect of fin spacing and fin height on the pool boiling performance. A high-speed camera was employed to capture the pool boiling process. A numerical investigation was also performed using the Eulerian multiphase model associated with the RPI wall boiling model. A 2-D rectangular boiling chamber filled with distilled water was considered for the numerical study. The numerical results with default models were validated with the experimental results. A correction was proposed for the Bubble Waiting Time coefficient (Cw) of the quenching heat flux to improve the numerical results. Experimental results showed that using rectangular and trapezoidal finned surfaces improved the heat flux values by 52.3% and 101.5%, respectively, compared to the plain surface. The heat transfer coefficient (HTC) depends upon the area availability and type of boiling surface used. Increasing the height of the fins was beneficial, whereas increasing the fin spacing adversely affected the fin performance. © 2023 Elsevier Ltd