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 Semi-Analytical Model for Bubble Departure Diameter Prediction for Triangular Grooved Surface(Toronto Metropolitan University, 2019) Sathyabhama, A.This paper presents experimental studies of pool boiling heat transfer from plain and triangular grooved surfaces to water at atmospheric pressure. Visualization technique is used to investigate the boiling phenomenon using high speed digital camera with image acquisition speed of 1000 fps at resolution of 320 x 240 pixels. It is observed that surface modification with grooves improves the boiling heat transfer. Various aspects of bubble behaviour on plain and grooved surfaces were investigated. The bubble generation frequency was higher for grooved surfaces. The average error in bubble departure diameter prediction of the semi-analytical model developed is 29.22%. © 2019, Toronto Metropolitan University. 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 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 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.