Faculty Publications
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Item Experimental investigation on heat transfer coefficients and frictional pressure drop during R134a condensation inside a plate-fin heat exchanger with wavy fin(Begell House Inc., 2018) Ramana Murthy, K.V.; Chennu, C.; Ashok Babu, T.P.; Luo, X.This paper presents the heat transfer coefficients and frictional pressure drops measured during the saturated vapor condensation of R134a inside a small plate-fin heat exchanger with wavy fin surface for air-conditioning systems in aircraft. The experiments were carried out at three different saturated temperatures (34°C, 38°C and 42°C). The effects of the saturation temperature, heat flux and mass flux on the mean condensation heat transfer coefficient and core frictional pressure drop were investigated experimentally and discussed in detail. The condensation heat transfer coefficients and frictional pressure drops are compared with serrated fin surfaces obtained in previous experiments. The correlations for heat transfer coefficient and frictional pressure drop during downward flow condensation of R134a inside the plate-fin heat exchanger with wavy fin are developed based on the experimental data. Compared with the serrated fins for saturated conditions of R134a at same mass flux and saturated temperature/pressure conditions, it is found that although the wavy fins have low condensation heat transfer coefficients, its two-phase frictional pressure drop is even lower than that of the serrated fins. Therefore, if the pressure drop limitation is critical, the wavy fins can be a good selection. © 2018 International Heat Transfer Conference. All rights reserved.Item Condensation heat transfer and pressure drop of R-134a saturated vapour inside a brazed compact plate fin heat exchanger with serrated fin(Springer Verlag service@springer.de, 2017) Ramana Murthy, K.V.; Chennu, C.; Ashok Babu, T.P.This paper presents the experimental heat transfer coefficient and pressure drop measured during R-134a saturated vapour condensation inside a small brazed compact plate fin heat exchanger with serrated fin surface. The effects of saturation temperature (pressure), refrigerant mass flux, refrigerant heat flux, effect of fin surface characteristics and fluid properties are investigated. The average condensation heat transfer coefficients and frictional pressure drops were determined experimentally for refrigerant R-134a at five different saturated temperatures (34, 38, 40, 42 and 44 °C). A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 22 kg/m2s. In the forced convection condensation region, the heat transfer coefficients show a three times increase and 1.5 times increase in frictional pressure drop for a doubling of the refrigerant mass flux. The heat transfer coefficients show weak sensitivity to saturation temperature (Pressure) and great sensitivity to refrigerant mass flux and fluid properties. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. Correlations are provided for the measured heat transfer coefficients and frictional pressure drops. © 2016, Springer-Verlag Berlin Heidelberg.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 SAS