Faculty Publications
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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 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 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.