Rheology of mineral oil-SiO2 nanofluids at high pressure and high temperatures

• Pressure dependence viscosity for nanofluids.
• non-Newtonian characteristics.
• Viscosity enhancement.
• Possible Chemical interaction between nanoparticle and basefluid at high pressure and temperature condition.

Nanofluids, engineered colloidal suspensions of nano-sized particles (less than 100 nm) dispersed in a basefluid, have shown potential for use as industrial cooling fluids due to their enhanced heat transfer capabilities. Many industrial applications often involve heat transfer fluids at pressures and temperatures above average atmospheric condition. Understanding the rheological characteristics of nanofluids is necessary for implementing them in these extreme conditions. Even though the effect of temperature on the viscosity of nanofluids at atmospheric pressure has been well studied, viscosity measurements of nanofluids at elevated pressures and temperatures have not yet been investigated. This work investigates the rheological characteristics of mineral oil based nanofluids at high pressure and high temperature (HPHT). The nanofluids used in this work were prepared by mechanically dispersing commercially available SiO2 nanoparticles (∼20 nm) in a highly refined paraffinic mineral oil (Therm Z-32, QALCO QATAR), which has wide applications in industrial heat exchangers. Mineral oil and nanofluids, with two volume concentrations of 1% and 2%, are studied in this work. The rheological characteristics of the basefluid and nanofluids are measured using an HPHT viscometer. During experimentation, viscosity values of the nanofluids are measured at pressures of 100 kPa and 42 MPa, with temperatures ranging from 25 °C to 140 °C, and at varying shear rates. The results show that the viscosity values of both nanofluids, as well as the basefluid, increased as the pressure increased. In addition, nanofluids exhibit non-Newtonian characteristics at elevated temperatures and pressures.