Experimental study on rheological behavior of water–ethylene glycol mixture in the presence of functionalized multi-walled carbon nanotubes A novel correlation for the non-Newtonian nanofluid Ehsan Shahsavani 1,2 • Masoud Afrand 1,2 • Rasool Kalbasi 1,2 Received: 3 July 2017 / Accepted: 12 September 2017 Ó Akade´miai Kiado´, Budapest, Hungary 2017 Abstract This paper examines the rheological behavior of water (60%vol.)–ethylene glycol (40%vol.) mixture in the presence of functionalized multi-walled carbon nanotubes. At the first, the viscosity of various samples was measured at shear rates ranging from 6.115 to 73.38 s -1 and tem- perature range of 25–50 °C. Then, using the experimental data, some correlations were proposed to predict the vis- cosity of the nanofluid. Viscosity measurements at different shear rates revealed that all nanofluid samples were non- Newtonian power law fluid. Findings showed that consis- tency index increased along with volume fraction, while it decreased with increasing temperature. Moreover, the values of power law index were always less than 1, indi- cating shear thinning behavior. Keywords Non-Newtonian behavior  F-MWCNTs/EG– water nanofluid  Viscosity measurements  Correlation Introduction In non-air-cooled internal combustion engines, heat exchangers, polymer industry and solar collectors, one or more fluids are used for heat exchange. The best, cheapest and most accessible material in this regard is water, which has a good thermal capacity and can transfer a significant amount of heat. However, despite having a high thermal capacity, water freezes at subzero temperatures. Freezing of water damages the conduits through which water flows. Adding ethylene glycol (EG) to water may solve this problem. EG considerably affects the freezing temperature of water and lowers it to -35 °C. Another very important property of antifreeze agents is their anti-corrosion prop- erty which is very useful. This important property is also referred to as the anti-corrosiveness of the fluid, which increases the heat exchange equipment’s lifetime. It also prevents material deposits, which leads to better heat exchange. However, it is known that ethylene glycol has a lower thermal conductivity than water, which reduces heat transfer. In recent years, researchers have tried to solve this problem by adding nanomaterials to EG or EG–water mixture [1–3]. The fluids that are produced by combining fluids with nanomaterials are called nanofluids. In recent years, extensive researches have been done on the prop- erties and flow of nanofluids, suggesting better thermal performance of nanofluid compared with conventional fluids [4–6]. Viscosity and thermal conductivity are important parameters in the study of heat transfer in fluids. For example, thermal conductivity directly affects heat transfer rate. Many researchers have shown that addition of nano- materials to the base fluid significantly increases the ther- mal conductivity [7–9]. Viscosity plays a key role in the calculation of heat transfer parameters (such as Prandtl number, Rayleigh number and Reynolds number). Exten- sive research in the field of nanofluids viscosity, a summary of which is presented in Table 1, shows that the viscosity of the base fluid increases by the addition of solid nano- materials. These studies, which are all based on Newtonian behavior of nanofluids, show that the viscosity of & Masoud Afrand masoud.afrand@pmc.iaun.ac.ir; masoud_afrand@yahoo.com 1 Department of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran 2 Modern Manufacturing Technologies Research Center, Najafabad Branch, Islamic Azad University, Najafabad, Iran 123 J Therm Anal Calorim DOI 10.1007/s10973-017-6711-8