Research on Theoretical Model of Dynamic Bulk Modulus of Gas-Containing Hydraulic Oil

The bulk modulus of the gas-containing hydraulic oil is an important indicator reflecting its compressibility, directly affecting the stability, accuracy, rapidity, and reliability of the fluid transmission system. In the time-varying system with high speed and pressure, since the gas release rate differs from the gas dissolution rate, there exists a large difference between the static and dynamic values of the bulk modulus of hydraulic oil. Therefore, it is necessary to research the dynamic bulk modulus of the gas-containing hydraulic oil. Based on the improvement of Henry's law and gas-polytropic-process equation, a modified model of dynamic bulk modulus of the gas-containing hydraulic oil was proposed. Through the analysis of parameter influence, the influence of initial gas content and pressure on the dynamic bulk modulus of the gas-containing hydraulic oil during compression and expansion was discussed. Comparing the modified model and the Zhou model with the experimental results, the goodness of fit between the Zhou model and the experimental results during compression and expansion was 0.9936 and 0.9864, respectively. And the goodness of fit between the modified model and the experimental results during compression and expansion was 0.9937 and 0.9936, respectively. The prediction precision of the dynamic bulk modulus was improved while verifying the accuracy of the modified model. This research can provide a reference for optimizing the theoretical model of the dynamic bulk modulus of the gas-containing hydraulic oil.