Modelling the Pressure and Temperature Dependence of Viscosity and Volume for Hydraulic Fluids

Viscosity and compressibility have a major impact upon the efficiency and dynamic response of fluid power systems. The viscosity and compressibility of five hydraulic fluids have been measured for temperatures to 150 °C and pressures to 350 MPa. A new correlation of viscosity with temperature and pressure based on the thermodynamic scaling rule of Roland et al. is offered. This correlation provides a means to model elastohydrodynamic effects in fluid power components and extends the accuracy of fluid power system models to higher pressure. The role of phase change and the resulting thixotropy in mineral based fluids is experimentally investigated.