Thermophysical properties of a nanofluid based on a eutectic mixture of dipheny and diphenyl oxide and carbon black nanoparticles

Abstract

Synthetic thermal oils are used as heat transfer fluids (HTFs) in different applications, due to their higher working temperature. In this way, one of the applications of interest is the use of thermal oils in Concentrated Solar Power (CSP) plants with Parabolic Trough technology. Nowadays, the HTF known commercially as Therminol VP1 (Solutia Inc.) is being used in CSP plants. This fluid is composed of a eutectic mixture of diphenyl (C12H10) and diphenyl oxide (C12H10O), and it is used as an HTF with a maximum working temperature of 400ºC. However, one of the drawbacks of Therminol VP1 is its low thermal conductivity. In recent years it has been demonstrated that the addition of nanoparticles can improve the thermal properties of HTFs, and they are then called nanofluids. The key factor of nanofluids is their high stability over time, understanding stability of a nanofluid as its capacity of keeping low agglomeration and sedimentation rates of nanoparticles. However, at high temperatures it is necessary to add chemically compatible surfactants that do not degrade and endow the nanofluids with stability through steric repulsion even under high temperature conditions. In this work, a carbon black/Therminol VP1 nanofluid was synthesized and stabilized using diphenyl sulfone as a stabilizer. Stability tests after thermal cycling at 400ºC showed the higher performance of this additive compared to others commonly used in the literature. Thermal conductivity, and heat capacity of the nanofluids at 3 vol% and 5 vol% were characterized from 50ºC to 350ºC.