1 3 J Braz. Soc. Mech. Sci. Eng. DOI 10.1007/s40430-016-0664-x TECHNICAL PAPER Effect of copper oxide nanoparticles on thermophysical properties of hydraulic oil-based nanolubricants Ankit Kotia 1 · Abhisek Haldar 1 · Ravindra Kumar 1 · Piyush Deval 1 · Subrata Kr Ghosh 1 Received: 15 August 2016 / Accepted: 19 October 2016 © The Brazilian Society of Mechanical Sciences and Engineering 2016 significantly contribute in the reduction of greenhouse gases [1]. Lubricants play a vital role in improving machine per- formance. Recently, many researchers have observed the improvement in properties of lubricants by dispersion of nanoparticle. However, the dispersion of nanoparticles sig- nificantly modifies the thermophysical properties of base fluid [2]. Aberoumand et al. [3] reported viscosity and ther- mal conductivity of nanolubricants as the most important parameter for the industrial applications and proposed the correlations for the same. Kole and Dey [4] used CuO nanoparticles in gear oil and observed a three times increase in viscosity with 2.5 % vol- ume fraction of nanoparticles. Particle aggregation was the main factor for such increment. Lijesh et al. [5] reported an increase in viscosity with dispersion of multi-walled carbon nanotubes (MWCNT) in mineral oils. Kotia and Ghosh [6] used Al 2 O 3 nanoparticles in gear oil and observed a 10.5 % increment in viscosity with 0.5 % particle volume fraction. Thottackkad et al. [7] observed increase in viscosity of CuO-engine oil (SAE15W40) nanolubricants with increase in particle volume fraction up to 60 °C, however, beyond this temperature no significant change was observed. Mostafizur et al. [8] reported that viscosity of nanofluid increases with particle volume fraction, and at 5 °C, incre- ment in viscosity was 14.47, 20.39, 21.38, 22.70 and 23.68 % higher than that of the base fluid with 0.5–2.5 % (increment 0.5 %) particle volume fractions, respectively. Chou and Lee [9] performed stress–strain test for nanodiamond-dispersed lubricants and reported that the Bingham Plastic model is the most suited for these nanolubricants. Rashin and Hemalatha [10] examined the viscosity of CuO-coconut oil nanolubricant with varying shear rate and observed non-Newtonian behaviour, which may be due to pseudoplastico property of nanolubricants. Sabiha et al. [11] reported the non-Newtonian behaviour of Abstract The effect of CuO nanoparticles on thermo- physical properties of hydraulic oil (SAE 68) used in heavy earth moving machinery has been experimentally evaluated in this paper. The results of Fourier transform infrared red spectroscopy show that the lubricant remains chemically stable in the presence of CuO nanoparticles. Dynamic light scattering results for particle size distribution have depicted that the size of agglomeration increases with an increasing CuO particle volume fraction which is confirmed by field emission scanning electron microscope images as well. Nanolubricants exhibit non-Newtonian behaviours with increasing CuO nanoparticles volume fraction. The existing theoretical models are found to be inappropriate to predict the viscosity with nanoparticles volume fraction. A correla- tion has been proposed between viscosity and particle vol- ume fraction on the basis of experimental results. Thermal conductivity of CuO-hydraulic oil also increases with an increase in CuO particle volume fraction. Keywords CuO nanoparticles · HEMM · Hydraulic oil · Nanolubricants · Thermal conductivity · Viscosity 1 Introduction Hydraulic excavator has got wide applications in construc- tion work, and improvement in its performance would Technical Editor: Cezar Negrao. * Subrata Kr Ghosh subratarec@yahoo.co.in 1 Department of Mechanical Engineering, Indian School of Mines, Dhanbad 826004, India