Study of Transient Vapor Cavitation in Series Pipe Systems

The phenomenon of vapor cavitation due to water hammer in steel and plastic pipes (polyethylene and PVC) is investigated experimentally using high frequency pressure transducers. A wave character with a gradually increasing frequency of pressure oscillations is found to be associated with vapor cavitation. The influence of wall elasticity, liquid evaporation duration, and steady-state losses on the maximum cavitation pressure is shown. A growing pressure reduction is accompanied by gas desorption from the liquid. The liberated air reduces the amplitude of the pressure increase and prolongs the period of oscillations. The maximum cavitation pressure increase, directly proportional to the pressure wave velocity, can be many times higher than the maximum water hammer pressure amplitude. For the short liquid evaporation duration (below 0.06 s) considered in the experiment, the first maximum increase is also distinctly higher than previously published. The frequency of the vapor cavitation pressure wave depends on the duration of the oscillations. For the test cases, the frequency increases during the cavitation from about 400 to 900 Hz for steel pipes and from about 300 to 600 Hz for plastic pipes.