Pipeline column separation flow regimes

A generalized set of pipeline column separation equations is presented desc ribing all conventional types of low-pressure regions. These include water hammer zones, distributed vaporous cavitation, vapor cavities, and shocks ( that eliminate distributed vaporous cavitation zones). Numerical methods fo r solving these equations are then considered, leading to a review of three numerical models of column separation. These include the discrete vapor ca vity model, the discrete gas cavity model, and the generalized interface va porous cavitation model. The generalized interface vaporous cavitation mode l enables direct tracking of actual column separation phenomena (e.g., disc rete cavities, vaporous cavitation zones), and consequently, better insight into the transient event. Numerical results from the three column separati on models are compared with results of measurements for a number of flow re gimes initiated by a rapid closure of a downstream valve in a sloping pipel ine laboratory apparatus. Finally, conclusions are drawn about the accuracy of the modeling approaches. A new classification of column separation (act ive or passive) is proposed based on whether the maximum pressure in a pipe line following column separation results in a short-duration pressure pulse that exceeds the magnitude of the Joukowsky pressure rise for rapid valve closure.