Kinematic Viscosity Prediction of Polyalkylene Glycol in a Deep-Sea Environment from Molecular Dynamics

Using water-glycol hydraulic fluid as a working medium is an important development direction in deep-sea hydraulic systems. Viscosity is an important parameter in the characterization of flow fields. The study of the viscosity characteristics of polyalkylene glycols as a water–glycol thickener in deep-sea environments can help to research the viscosity properties of water glycol hydraulic fluid under deep-sea conditions. In this paper, a molecular dynamics method is used to compute the kinematic viscosity of PAG 75-W-130 based on the OPLS-AA force field. Dynamic viscosity was calculated by the nonequilibrium molecular dynamics method. At ambient pressure and temperatures from 293.15 to 373.15 K, the calculated density is in accord with the experimental results and the calculated viscosity is more than the experimental result. Moreover, the density and dynamic viscosity of PAG 75-W-130 are predicted in a deep-sea environment. The calculated viscosity and density increase exponentially with increasing pressure. The density increases from 1069.2 to 1110.4 kg/m³ at full sea depths, and the viscosity is up to 10.99 Pa·s at the sea depth of 11,000 m.