Determination of Undissolved Air Content in Oil by Means of a Compression Method

Abstract

This article describes a combination of experimental and mathematical methods for the determination of undissolved air content in hydraulic oil. The experimental part consists of the determination of the oil bulk modulus, considering the influence of undissolved air by means of a volume compression method in a steel pipe. A multiphase model of an oil/undissolved air mixture is subsequently defined using Matlab SimHydraulics software. The multiphase model permits the volume compression of oil and air bubbles independently of each other. Furthermore, time dependencies of pressures are mathematically simulated during the compression of the multiphase mixture of oil and undissolved air for different concentrations of the latter. The undissolved air content is determined by comparing the mathematically simulated and experimentally measured time dependencies of pressure increases. Highlights • Experimental determination of secant bulk modulus and tangent bulk modulus of oil by means of a compression method. • Multiphase mathematical model of compressibilityof oil/undissolved air mixture. • Mathematical simulation and measurement of time dependence of pressure during compression of oil/undissolved air mixture in steel pipe. • Determination of undissolved air content in oil by comparing the mathematical model with the measurement. • The undissolved air concentrations in the measured hydraulic system were determined in the range of 0.22 % to 0.49 %.

Modeling Study on Stiffness Characteristics of Hydraulic Cylinder under Multi-Factors

“…Since different hydraulic cylinder structures have different sizes, the levels need to be demonstrated according to Eqs. (2), (3), (7), (11), (12), and (16). After that, accept or reject each factor according to the accuracy requirements of the hydraulic cylinder stiffness.…”

“…According to Eqs. (2), (3), (7), (11), (12), and (16), the values of the hydraulic cylinder stiffness and the stiffness produced by each factor can be calculated respectively. Then the percentage of the stiffness produced by each factor relative to the hydraulic cylinder stiffness is also calculated.…”

“…(12) and the bulk modulus E o of the oil in Eq. (16), and to verify Eq. (2) of the hydraulic cylinder's stiffness mathematical model, the experimental study is carried out with the locked head chamber of the hydraulic cylinder.…”

“…The oil bulk modulus E o considering the different air content rates and work pressures can be describe in Eq. (17), [16] and [17].…”

Mathematical simulation and measurement of expansion of hydraulic hose with oil

“…This bulk modulus does not include the effect of the undissolved air content, which is separately entered. Air bubbles occur in oil in dissolved and undissolved forms [10]. Release and dissolution of air bubbles is given by the Henry's law [11].…”