Faculty Publications
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Item Experimental investigation on boiling heat transfer coefficient enhancement using grooves for cooling of electronic devices(Institute of Electrical and Electronics Engineers Inc., 2014) Sathyabhama, S.; Pandiyan, S.P.This paper presents the experimental investigation of pool boiling heat transfer performance of copper plain and grooved horizontal circular surfaces immersed in saturated water at atmospheric pressure. Effect of geometric parameters of the groove on boiling heat transfer coefficient was studied. Experimental results showed significant increase in boiling heat transfer coefficients at high heat flux with the provision of grooves. An increase in boiling heat transfer was observed with increase in fin thickness and groove depth. © 2014 IEEE.Item Nucleate pool boiling heat transfer from a flat-plate grooved surface(Begell House Inc. orders@begellhouse.com, 2015) Sathyabhama, S.This paper presents the experimental investigation of pool boiling heat transfer performance of copperplain and grooved horizontal circular surfaces immersed in saturated water at atmospheric pressure. The effect of the geometric parameters of the groove on boiling heat transfer was studied. From the experimental results, it was observed that the enhanced surfaces have a positive effect on the heat dissipation and the effect is greater than in the case of a plain surface. It was found that the heat dissipation increases with increasing groove depth, decreasing groove angle, and decreasing channel width. The improved heat transfer is attributed to improved bubble dynamics, which are a function of the heat transfer area, bubble escape resistance, and capillary force. The dominance of any of these factors over the other depends on a particular specimen. The modified Rohsenow correlation predicts the present experimental data with an error of ±20%. © 2015 by Begell House, Inc.Item Numerical investigation on subcooled boiling heat transfer coefficient of water-ethanol mixture by CISCAM technique(Korean Society of Mechanical Engineers, 2023) Suhas, S.B.; Mangrulkar, C.K.; Umashankar, K.K.K.; Sathyabhama, S.The subcooled flow boiling (SFB) of a water-ethanol mixture are relevant in operating heat-dissipating devices, such as smaller catalytic reactors, electronic apparatus, and hybrid electric vehicle battery components. The operative temperature should always be at a sustainable value to evade the failure or breakdown of these heat-dissipating devices. To cool these devices, a water-ethanol mixture is used as a coolant. The forced convective as well as SFB heat transfer coefficients (HTCs) for the water-ethanol mixture are estimated numerically using the volume of fluid method in a rectangular channel with dimensions of 15 mm×15 mm×150 mm. During SFB, the liquid-vapor interaction is examined by solving the bubble void fraction (BVF). For the discretization process, the Crank-Nicholson implicit method (scheme) is used, and the convective equation for the BVF is converted to an algebraic equation. The corrector predictor equation procedure is used for solving the BVF. The thermodynamic and thermophysical parameters related to subcooled boiling are estimated upon the incorporation of the bubble void fraction (α) using the mixture rule. These parameters are then incorporated into the x-momentum equation as well as into the energy equation for finding the fluid temperature, velocity, and pressure drop values. From the estimated values of temperature, subcooled flow boiling HTC is obtained. The estimated values of HTC can predict well compared with that of empirical equations. Moreover, mass flux plays a vital role in the forced convective region, while heat flux has a crucial role in the SFB region for the improvement of HTC. © 2023, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.Item Experimental investigation on flow boiling characteristics of the ethanol–water mixture in conventional channels(Springer Science and Business Media Deutschland GmbH, 2023) Krishnegowda, M.; Sathyabhama, S.The flow boiling heat transfer characteristics of the ethanol–water mixture (25%/75% by volume) and its pure constituents was experimentally investigated in conventional channels. The experiments were conducted for different ranges of mass flux, heat flux, subcooled inlet temperature and two different aspect ratios (AR). Flow patterns recorded by high-speed camera indicated that the bubble waiting and the growth period are minimum for the mixture and maximum for the ethanol, resulting in a higher heat transfer coefficient (HTC) for the mixture and lower HTC for ethanol in both the channels. For all the working fluids, high HTC was observed for the channel of AR = 1.25 in the forced convective region, whereas in the subcooled boiling region, high HTC was observed for the AR = 0.2 channel. The average subcooled HTC obtained for the 25% ethanol–water mixture was 15.75% and 38.85% higher than that of water and ethanol respectively for the AR = 0.2 channel. However, it was 18.11% and 41.2% higher than that of water and ethanol for the AR = 1.25 channel. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Enhanced boiling heat transfer of water on a liquid-infused surface(Elsevier Ltd, 2023) Prasad Yandapalli, A.V.V.R.; Moreno Resendiz, E.M.; Kuravi, S.; Sathyabhama, S.; Kota, K.The aim of this study was to experimentally demonstrate a counter-intuitive phenomenon that a surface covered with a liquid has the potential for enhancing heat transfer for the boiling of water over it. To this end, a highly-wetting surface with a zero contact angle for multiple liquids, i.e., an Ultra-Omniphilic Surface (UOS) was prepared on aluminum (Al 6061 alloy) using a simple and easy-to-implement bulk micro-manufacturing approach and a non-boiling liquid (NBL) was infused over this surface to occupy its sub-surface micro/nano-cavities. The resulting liquid-infused UOS is called a Binary Surface (BiS) for it has two distinct superficial phases — solid phase as islands and liquid phase as NBL puddles. Saturated nucleate pool boiling experiments were conducted on the BiS and the critical heat flux (CHF) and the boiling heat transfer coefficient (HTC) were measured. The results were compared with the UOS and a plain/polished surface (PS) prepared from the same aluminum alloy sample. In addition, high-speed visualization was employed for capturing the bubble dynamics at different heat fluxes and parameters such as bubble departure diameter (Dd), bubble departure frequency (f), and nucleation site density (NSD) were measured. The results revealed that the nucleate pool boiling performance of water on the BiS surpasses both the PS and the UOS. The HTC on the BiS was 1.33 times and two times larger than the UOS and the PS, respectively. The CHF obtained on the BiS was comparable to that on the UOS and 1.47 times larger than that on the PS even though a considerable portion of the BiS surface area was covered with the NBL and unavailable for boiling. Remarkably, an inspection of the high-speed videos has suggested the presence of the same NBL as the reason for the better boiling heat transfer performance of the BiS. The NBL that was spread over the BiS as puddles was found to (1) prevent the growth of large vapor bubbles and (2) extend the isolated bubble regime by delaying the lateral coalescence of adjacent bubbles. A comparison of the results between UOS and BiS suggests that – as far as boiling enhancement is concerned – mechanisms for tackling vapor bubbles could be superior to those that involve improving surface wettability. © 2023