Viscosity Prediction of Water-Containing Hydraulic Oil in the Deep-Sea Environment Using Molecular Dynamics Simulations

MJ Shen and YS Liu and XP Zhou, JOURNAL OF CHEMICAL AND ENGINEERING DATA, 70, 2698-2712 (2025).

DOI: 10.1021/acs.jced.5c00127

10# aviation hydraulic oil serves as the main working fluid in deep-sea hydraulic systems that operate under high-pressure and low-temperature conditions. Seawater penetration gradually raises water content, altering the viscosity and consequently affecting system performance. However, the effect of water on the viscosity of hydraulic oil under deep-sea conditions remains poorly understood. This study employs molecular dynamics simulations to estimate the viscosity of hydraulic oil mixed with 0-7 wt % water under deep-sea conditions. At atmospheric pressure and different temperatures, the viscosity increases by 25.67% to 27.75% as the water content rises from 0 to 7 wt %. The predicted values are slightly higher than the experimental results. Moreover, the predicted viscosity of water-containing hydraulic oil under deep-sea conditions increases exponentially with pressure. At a sea depth of 11 km, the viscosity of hydraulic oil containing 7 wt % water reaches 431.98 mPas, which is approximately 23 times higher than that of pure oil at atmospheric pressure. To elucidate the molecular mechanism by which water affects viscosity, the interaction energy, microscopic structure, and diffusion coefficient are analyzed. Furthermore, an empirical formula is proposed to predict the viscosity of water-containing hydraulic oil as a function of pressure, temperature, and water content under deep-sea conditions.

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