In many industrial applications the liquid trapped inside long pipelines can cause a number of problems. Intrusion of the pressurized air on top of the water column inside the horizontal pipeline can result in a less or more mixed stratified flow. The dynamics of a moving air–water front during the emptying of a PVC pipeline with the diameter-to-length ratio 1 : 1100 were experimentally and theoretically studied. In the experiments, the water was driven out of the pipeline with an initial upstream air pressure of 2 barg and a 4.5 m high downstream-end siphon, where the water outflow was restricted by a valve that was closed 11%. The measured discharges and water-level variations are analysed together with Control Volume modelling results. During the ‘forced’ (not only gravity-driven) emptying process, both the downstream-end drainage and tail leakage behind the moving air–water front decreased over the full water-column length. The water-column mass loss due to the tail leakage is referred to as holdup. The Zukoski dimensionless number is used to parameterize the relative shortening of the water column associated with the unidirectional movement of the air–water front along the large-scale horizontal test section of the pipeline, where surface-tension effects and minor losses at joints and turns are negligible.
Benjamin, T. B. 1968. Gravity currents and related phenomena. J. Fluid Mech., 31(2), 209–248.
http://dx.doi.org/10.1017/S0022112068000133
Bergant, A. and Simpson, A. R. 1999. Pipeline column separation flow regimes. ASCE J. Hydraul. Eng., 125(8), 835–848.
http://dx.doi.org/10.1061/(ASCE)0733-9429(1999)125:8(835)
Bergant, A., Simpson, A. R., and Tijsseling, A. S. 2006. Water-hammer with column separation: a historical review. J. Fluid Struct., 22(1), 135–171.
http://dx.doi.org/10.1016/j.jfluidstructs.2005.08.008
Bergant, A., van ’t Westende, J. M. C., Koppel, T., Gale, J., Hou, Q., Pandula, Z., and Tijsseling, A. S. 2010. Water hammer and column separation due to accidental simultaneous closure of control valves in a large scale two-phase flow experimental test rig. In Proceedings of the ASME 2010 Pressure Vessels & Piping Division/K-PVP Conference. Bellevue, Washington, USA. Paper PVP2010–26131, Vol. 3, pp. 923–932.
Bergant, A., Hou, Q., Keramat, A., and Tijsseling, A. S. 2011. Experimental and numerical analysis of water hammer in a large-scale PVC pipeline apparatus. In Proceedings of the 4th IAHR International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems (Belgrade, Serbia, October 2011), pp. 27–36.
Bozkus, Z. and Wiggert, D. C. 1997. Liquid slug motion in a voided line. J. Fluid Struct., 11(8), 947–963.
http://dx.doi.org/10.1006/jfls.1997.0112
Collins, R. P., Boxall, J. B., Karney, B. W., Brunone, B., and Meniconi, S. 2012. How severe can transients be after a sudden depressurization? J. Am. Water Works Ass., 104(4), E243–E251.
http://dx.doi.org/10.5942/jawwa.2012.104.0055
Hou, Q., Tijsseling, A. S., Laanearu, J., Annus, I., Koppel, T., Bergant, A., Vučkovič, S., Gale, J., Anderson, A., van ’t Westende, J. M. C., Pandula, Z., and Ruprecht, A. 2012. Experimental Study of Filling and Emptying of a Large-scale Pipeline. External Report, CASA Report No. 12-15. Technische Universiteit Eindhoven, Eindhoven.
Hou, Q., Tijsseling, A. S., Laanearu, J., Annus, I., Koppel, T., Bergant, A., Vučkovič, S., Anderson, A., and van ’t Westende, J. M. C. 2014. Experimental investigation on rapid filling of a large-scale pipeline. ASCE J. Hydraul. Eng., 140(11), 04014053.
http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000914
Laanearu, J. and van ’t Westende, J. 2010. Hydraulic characteristics of test rig used in filling and emptying experiments of large-scale pipeline. In Proceedings of the Hydralab III Joint Transnational Access User Meeting, Hannover, 2–4 February 2010. Coastal Research Centre FZK of Leibniz University and Technical University of Braunschweig, Hannover, Germany, pp. 5–8.
Laanearu, J., Annus, I., Koppel, T., Bergant, A., Vučkovič, S., Hou, Q., Tijsseling, A. S., Anderson, A., and van ’t Westende, J. M. C. 2012. Emptying of large-scale pipeline by pressurized air. ASCE J. Hydraul. Eng., 138(12), 1090–1100.
http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000631
Laanearu, J., Annus, I., Sergejeva, M., and Koppel, T. 2014. Semi-empirical method for estimation of energy losses in a large-scale pipeline. Procedia Engineering, 70, 969–977.
http://dx.doi.org/10.1016/j.proeng.2014.02.108
Martin, C. S. and Lee, N. 2012. Measurement and rigid column analysis of expulsion of entrapped air from a horizontal pipe with an exit orifice. In Proceedings of the 11th International Conference on Pressure Surges. BHR Group, Lisbon, Portugal, pp. 527–542.
Martinoia, T., Barreto, C. V., da Rocha, J. C. D. C., Lavoura, J., and Henriques, F. M. P. 2012. Simulation and planning of pipeline emptying operations. In Proceedings of the 9th International Pipeline Conference. ASME, Calgary, Alberta, Canada, Paper No. IPC2012-90432, pp. 603–611.
Pozos, O., Gonzalez, C. A., Giesecke, J., Marx, W., and Rodal, E. A. 2010. Air entrapped in gravity pipeline systems. J. Hydraul. Res., IAHR, 48(3), 338–347.
http://dx.doi.org/10.1080/00221686.2010.481839
Tijsseling, A. S., Hou, Q., and Bozkus, Z. 2014. An improved 1D model for liquid slugs travelling in pipelines. In Proceedings of the ASME 2014 Pressure Vessels & Piping Division Conference, Anaheim, California, USA. PVP2014–28693.
Zukoski, E. E. 1966. Influence of viscosity, surface tension, and inclination angle on motion of long bubbles in closed tubes. J. Fluid Mech., 25(4), 821–837.http://dx.doi.org/10.1017/S0022112066000442
