Faculty Publications
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Item Influence of surface roughness on pool boiling heat transfer(Institute of Physics Publishing helen.craven@iop.org, 2018) Walunj, A.; Sathyabhama, A.Experimental study of pool boiling heat transfer from the rough surface at pressure 1 bar, 5 bar and 10 bar is presented. Experiments are carried on 20 mm diameter copper sample at saturated condition of distilled water. Unidirectional scratches are made by different grit sandpaper. The surface roughness value Ra is varied from 0.106 μm to 4.03 μm. The effect of Ra on heat transfer at different pressure is reported. The variation in heat transfer coefficient with the heat flux for samples of different Ra is also examined. The predicted critical heat flux (CHF) by Kim's model is found to in good agreement with present experimental values with mean absolute error of 12.06%. © Published under licence by IOP Publishing Ltd.Item Bubble dynamics in pool boiling on rough surface under exponential heat supply(Begell House Inc. orders@begellhouse.com, 2018) Walunj, A.; Sathyabhama, A.In this paper, bubble dynamics in the pool boiling of distilled water on the horizontal copper test sample of 20 mm diameter at atmospheric pressure is studied. The experiments are carried under steady and exponential heat supply of γ=1 to rough copper sample with Ra ranging from 0.106 μm to 4.03 μm. The high speed camera of 1000 fps is used to observe the bubble morphology. The effect of surface roughness on boiling heat transfer during transient heat supply is reported. The effect of surface roughness on bubble departure diameter and bubble frequency is studied. The waiting time and growth time of the bubble for different samples is also compared. The effect of steady and exponential heat supply on bubble departure diameter and bubble frequency is also reported. © 2018 Begell House Inc.. All rights reserved.Item Effect of Surface Roughness on Pool Boiling Characteristics under Variable Heat Supply(Toronto Metropolitan University, 2019) Walunj, A.; Sathyabhama, A.An experimental investigation of critical heat flux (CHF) for boiling heat transfer from the rough copper sample under steady and quasi-steady exponentially varying heat supply is presented in this paper. The unidirectional scratches are made on the 20 mm diameter copper sample to obtain a wide range of surface roughness, ranging from Ra=0.106 μm to Ra=4.03 μm. The boiling characteristics for steady and transient-state conditions are compared by considering the onset of boiling (ONB) and CHF. The effect of surface roughness on the surface wettability and CHF are also studied. The enhancement in the transient CHF for the roughest sample (Ra=4.03 μm) is found to be 98.88%. The Rohsenow correlation for heat transfer coefficient (HTC) is modified, which predicts the present experimental data of HTC with mean absolute error (MAE) of 10.36%. The hydrodynamic model with capillary wicking force predicts the CHF for a wide range of Ra with a mean absolute error of 4.14%. © 2019, Toronto Metropolitan University. All rights reserved.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.