Waterhammer in Quick Opening of a Closed Pipe with a Cooling Cavity

Abstract

Since a closed pipe maintains a low pressure near saturation vapor pressure during the formation of a cooling cavity, quickly opening a valve at an end of the pipe collapses the cavity due to the impressed atmospheric pressure, and it gives rise to a strong waterhammer of the pressure-impression type, in which the difference in pressures between the outside and inside of the pipe collapses the cavity. The above phenomenon is modeled by the rigid column theory. Formulas to estimate the maximum pressure rise are derived using the volumetric fraction of the cavity, the impression pressure difference, the mass density and the sonic velocity of the liquid in the pipe. Calculated curves are compared with the idealized experimental data. Because of air containment, the cavity does not completely vanish and some bubbles of air remain after the collapse. A weak buffer effect of the air in the cavity is shown quantitatively by the experiment.