WATER VAPOUR CAVITATION IN HYDRAULIC FLUIDS

摘要

Cavitation in hydraulic systems leads to cavitation erosion which ultimately results in system failure [1, 2] and the reduction of the systems' stiffness. There are three types of cavitation known: gas, vapour and pseudo cavitation [3]. In previous gas-cavitation studies enormous air release rates in hydraulic fluids have been discovered which could not be explained just by the diffusion of dissolved air through bubble's boundary. A possible explanation is the simultaneous occurrence of vapour cavitation in conjunction with gas-cavitation. However, this requires drastic pressure drops below several Pa, which is hard to achieve in hydraulic systems. This article introduces a further hypothesis for the unexplainable air release rates as fourth type of cavitation. Technical fluids can dissolve other fluids, such as water, to a degree which evaporate at much higher pressures compared to the base fluid. Based on a standard HLP 46 hydraulic oil and water as dissolved fluid, the presented hypothesis is verified. Firstly, a phenomenological mathematical model is developed. Subsequently, a test rig is presented to prove the hypothesis.