Abstract
A mathematical model is presented for numerical simulation of the fluid transients in the return line during the decompression operation of a hydraulic system. Particular attention has been paid to clarification of the influence of gas diffusion on the fluid transients because in such a system, part of the separation cavity consists of a gas-liquid two-phase flow containing a number of minute gas (air) bubbles. Experiments using sump oil and deaerated oil as a test fluid showed that the generation mechanism of the separation cavity and the fluid transients are significantly affected by the gas diffusion. Values calculated from the proposed "bubble-diffusion model", which takes into consideration the effects of gas diffusion as well as the amount of gas bubbles released from the oil flowing out of the valve before column separation occurs, the change of state of gas and the surface tension applied to the gas bubble, agreed well with the measured values over a wide range of tests.
