Abstract
A pipe water hammer with column separation was studied in a range of flow rates (Re=465 to 2239) in a test rig with an acrylic glass observation section. Pressure transients were measured with piezoresistive pressure sensors, while the gas evaporation and condensation were captured by high-speed recording with a Photron SA-Z at a frame rate of 75,000 fps. Separation lengths were estimated by a threshold value in the images. The results did not show a sharp gas–oil interface but consisted of small, dispersed bubbles mixed with larger vapor structures, where the bubbles seemed to become smaller after each collapse. These findings differ from the transient cavitating characteristics commonly reported in nonhydraulic piping systems governed by different fluid properties and time scales. Good repeatability, both in terms of pressure transients and bubble distribution, was observed. The column separation was quantified as a metric of separation length, which was consistent between the tests. Combined with pressure measurements, these results may assist in obtaining a better understanding of the transient cavitation dynamics within oil–hydraulic systems as well as be used to improve modelling strategies towards more accurate cavitation erosion predictions.
Highlights
Cavitation erosion is a major concern in most hydraulic applications such as turbines, pumps, and hydraulic percussion units [1]
At the intermediate flow rate (Figure 4b), the column separation was not very prominent, small pressure spikes were visible in addition to the water hammer pressure
The oil–hydraulic column separation observed in our previous study using a steel pipe [3] was confirmed by reproducing the experiments with a transparent pipe made of acrylic glass
Summary
Cavitation erosion is a major concern in most hydraulic applications such as turbines, pumps, and hydraulic percussion units [1]. In the latter case, constant changes in pressure and flow direction will cause water hammer events with possible column separation. Constant changes in pressure and flow direction will cause water hammer events with possible column separation Collapsing bubbles cause both pressure waves and high-speed jets which could induce cavitation erosion. The processes for bubble collapse and cavitation erosion are very short and typically happen on a time scale of microseconds [2]. Repetitive water hammerinduced cavitation may promote erosion in crucial parts of the machinery [3]. Parts that are subject to severe erosion should be cheap and easy to replace
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