Abstract
The flow pattern and its transition of the mixture of nitrogen gas and water are observed in U-tubes and inverted U-tubes using high speed CCD camera. In U-tube, it is observed that the dispersed bubble before U-bend converges to be Taylor bubble after U-bend; the Taylor bubble to the slug bubble and the smaller slug bubble to the larger one. And, the slug bubble merges before U-bend and separates in U-bend and finally develops slug bubble again after U-bend. In addition, the film falling annular flow before U-bend and shear in U-bend and at last form Taylor bubble or slug bubble after U-bend. Besides, a different freezing plug in U-tubes is observed. In inverted U-tube, the converging transition observed is from Taylor bubble to slug bubble, Taylor bubble to film falling annular, and slug bubble to film falling annular. At last, the flow pattern map for U-tubes and inverted U-tubes is proposed, respectively.
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References
Dean WR (1928) The stream line motion of fluid in a curved pipe. Philos Mag 5:673–695
Dean WR (1927) Note on the motion of fluid in a curved pipe. Philos Mag 4:208–223
Traviss DP, Rohsenow WM (1973) The influence of return bends on the downstream pressure drop and condensation heat transfer in tubes. ASHRAE Trans 79:129–137
Da Silva Lima RJ, Thome JR (2012) Two-phase frictional pressure drops in U-bends and contiguous straight tubes for different refrigerants, orientations, tube, and bend diameters: Part 1. Experimental results (RP-1444). HVAC&R Res 18:1047–1071. doi:10.1080/10789669.2012.672362
Da Silva Lima RJ, Thome JR (2012) Two-phase flow patterns in U-bends and their contiguous straight tubes for different orientations, tube and bend diameters. Int J Refrig 35:1439–1454. doi:10.1016/j.ijrefrig.2012.02.002
Wang C–C, Chen IY, Yang Y-W, Chang Y-J (2003) Two-phase flow pattern in small diameter tubes with the presence of horizontal return bend. Int J Heat Mass Transf 46:2975–2981. doi:10.1016/s0017-9310(03)00071-1
Wang C–C, Youn Chen I, Yang Y-W, Hu R (2004) Influence of horizontal return bend on the two-phase flow pattern in small diameter tubes. Exp Thermal Fluid Sci 28:145–152. doi:10.1016/s0894-1777(03)00033-5
Wu HL, Peng XF, Ye P, Eric Gong Y (2007) Simulation of refrigerant flow boiling in serpentine tubes. Int J Heat Mass Transf 50:1186–1195. doi:10.1016/j.ijheatmasstransfer.2006.10.013
de Matos A, Franca FA (2009) Bubbly flow segregation inside a U-bend pipe: experimentation and numerical simulation. Chem Eng Res Des 87:655–668. doi:10.1016/j.cherd.2008.08.015
Donaldson AA, Kirpalani DM, Macchi A (2011) Single and two-phase pressure drop in serpentine mini-channels. Chem Eng Process Process Intensif. Accepted manuscript doi:10.1016/j.cep.2011.05.002
Wang C–C, Chen IY, Lin Y-T, Chang Y-J (2008) A visual observation of the air-water two-phase flow in small diameter tubes subject to the influence of vertical return bends. Chem Eng Res Des 86:1223–1235. doi:10.1016/j.cherd.2008.06.008
Padilla M, Revellin R, Bonjour J (2012) Two-phase flow visualization and pressure drop measurements of HFO-1234yf and R-134a refrigerants in horizontal return bends. Exp Thermal Fluid Sci 39:98–111. doi:10.1016/j.expthermflusci.2012.01.013
Mandhane JM, Gregory GA, Aziz K (1974) A flow pattern map for gas–liquid flow in horizontal pipes. Int J Multiph Flow 1:537–553. doi:10.1016/0301-9322(74)90006-8
Taitel Y, Dukler A (1976) A model for predicting flow regime transitions in horizontal and near horizontal gas–liquid flow. AIChE J 22:47–55
Traviss D, Rohsenow W (1973) Flow regimes in horizontal two-phase flow with condensation. ASHRAE Trans 79:31–39
Baker JL (1965) Flow-regime transitions at elevated pressures in vertical two-phase flow Argonne National Lab., Ill. Associated Midwest Universities, Lemont, Ill
Chen IY, Yang Y-W, Wang C–C (2002) Influence of horizontal return bend on the two-phase flow pattern in a 6.9 mm diameter tube. Can J Chem Eng 80:478–484. doi:10.1002/cjce.5450800317
Wang C–C, Chen IY, Huang P-S (2005) Two-phase slug flow across small diameter tubes with the presence of vertical return bend. Int J Heat Mass Transf 48:2342–2346. doi:10.1016/j.ijheatmasstransfer.2004.12.036
Usui K (1980) Flow behavior and pressure drop of two-phase flow through C-shaped bend in vertical plane, (I): upward flow. J Nucl Sci Technol 17:875–887
Usui K (1981) Flow behavior and pressure drop of two-phase flow through C-shaped bend in vertical plane, (II) downward flow. J Nucl Sci Technol 18:179–190
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This work is supported by the National Natural Science Foundation for Young Scholars of China (Grant No. 50806042).
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Deng, D., Wang, R.S., Xie, S.W. et al. Flow pattern and its transition of nitrogen gas–water two-phase flow in U-tubes and inverted U-tubes. Heat Mass Transfer 51, 85–94 (2015). https://doi.org/10.1007/s00231-014-1395-0
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DOI: https://doi.org/10.1007/s00231-014-1395-0