Experimental Investigation of Column Separation Using Rapid Closure of an Upstream Valve

Abstract

In this study, the phenomenon of column separation that occurs in the downstream pipeline of a rapid closure valve is experimentally investigated. Special attention is paid to the dynamic behavior of the formation, growth, and collapse processes of cavities, which are observed using a high-speed camera. Synchronized images of cavity patterns and measured pressure histories are analyzed to elucidate the process of water column separation, the mechanism of column separation events, and the influence of parameters on the transient flow. Experimental results indicate that during the collapse process of vapor cavities, a superposition phenomenon involving a positive pressure wave and collapse wave occurs, resulting in a nearly three times rise of Joukowsky pressure. In all test cases, the maximum pressure of the pipeline exceeded 150 times the reservoir static pressure. A new classification for a water hammer combined with cavitation (four types of pressure oscillation patterns) is proposed based on whether the duration of column separation decreases sequentially and the maximum pipeline pressure follows the first collapse of cavities at the valve. As the initial flow velocity increases, there is generally an increase in maximum pressure; however, this trend may be scattered under certain operation conditions.

Application of linear impulse momentum theory to the hammering problem

“…Several researchers attempted to work on the hydraulic model under transient conditions while exposed to rising pressure problem. Experiments reveal that over cavitation, the pressure can rise to approximately three times the value predicted by the Joukowsky equation, revealing that the equation overestimates the pressure in such circumstances 7 . The typical experiment setup involved two reservoirs (upstream and downstream), a "non-ori ce" ow, an extended pipe, and valves to investigate when a valve closes swiftly for the case of cavities generation and the case without cavitation with similar result of Joukowsky formula deviation from the experimental results 8 .…”

“…Recent experimental results Wang et al 7 and Jiang et al 8 show that there is a trend in very high pressure rise for the two tanks system, with a similar lower pressure rise that is up to three times less than the Joukowsky formula, but with a different condition of low range of pressure difference that causes cavitation just after rapid closure of the valve. In these tests, they used a similar experimental setup that included pressure tanks capable of handling higher heads, which is an analogy for what many valves encounter in the eld.…”

“…3, the change in pressure will be computed in Eq. (7) 7 where E o and E v are the elevation of the base of source tank and vavle elevation in meter respectivly. The H o and H v are the total head of in ow tank and valve location in meter.…”