Faculty Publications
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Item Flow boiling heat transfer and pressure drop analysis of R134a in a brazed heat exchanger with offset strip fins(Springer Verlag service@springer.de, 2017) Amaranatha Raju, M.; Ashok Babu, T.P.; Chennu, C.The saturated flow boiling heat transfer and friction analysis of R 134a were experimentally analyzed in a brazed plate fin heat exchanger with offset strip fins. Experiments were performed at mass flux range of 50–82 kg/m2 s, heat flux range of 14–22 kW/m2 and quality of 0.32–0.75. The test section consists of three fins, one refrigerant side fin in which the boiling heat transfer was estimated and two water side fins. These three fins are stacked, held together and vacuum brazed to form a plate fin heat exchanger. The refrigerant R134a flowing in middle of the test section was heated using hot water from upper and bottom sides of the test section. The temperature and mass flow rates of water circuit is controlled to get the outlet conditions of refrigerant R134a. Two-phase flow boiling heat transfer and frictional coefficient was estimated based on experimental data for offset strip fin geometry and presented in this paper. The effects of mass flux, heat flux and vapour quality on heat transfer coefficient and pressure drop were investigated. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier ?f, and Martinelli parameter X. © 2017, Springer-Verlag Berlin Heidelberg.Item Investigation of flow boiling heat transfer and pressure drop of R134a in a rectangular channel with wavy fin(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2020) Amaranatha Raju, M.; Ashok Babu, T.P.; Chennu, C.The saturated flow boiling heat transfer and pressure drop studies of R134a were experimentally investigated in a rectangular channel with wavy fin. Experiments were performed at mass flux range 30–50 kg m?2 s?1, heat flux range 11–18 kW m?2 and quality 0.26–0.8. The experimental data were obtained in a brazed test section. In preliminary step, single phase experiments were conducted to find out the j and f data of the wavy fin. In second step, two-phase flow boiling experiments were conducted to estimate the heat transfer and frictional coefficient based on experimental data. The trends of heat transfer and pressure drop with respect to mass flux, heat flux and quality were studied. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier, ?f and Martinelli parameter, X. © 2019 Elsevier Masson SASItem 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.