Effects of doping on the thermophysical properties of Ag and Cu doped TiO2 nanoparticles and their nanofluids

[Display omitted] •A temperature-based equation for the specific heat of pure and Ag/Cu-doped TiO2 particles was proposed.•The highest specific heat (3051.31 J/kgK) was obtained at the highest doping rate (0.3 %) with the lowest mass concentration.•The specific heat decreases with increasing particle concentration, and the highest decrease was 48.2%.•Thermal conductivity increased by 2.40% and 1.89% with increasing doping ratio and concentration, respectively.•Viscosity increases up to 75.21% by concentration increase, while no significant change was observed for doping increase. A widely accepted method to improve the thermal performance of nanofluids is adding more particles to the fluid, which often causes higher viscosity and sedimentation risk. Therefore, alternative methods are required to create complex structures and improve the properties of particles to acquire similar or even better performance with a smaller amount. Doping is one of the promising methods, and this study examined the effects of doping rates (0.1 and 0.3 %) and materials (Ag and Cu) on the thermophysical properties of ethylene glycol-water-based nanofluids. Nanofluids were prepared with pure and Ag/Cu doped TiO2 nanoparticles at various concentrations (0.3 %, 0.5 %, 1 %, and 2) by mass. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), particle size distribution (PSD), Brunauer, Emmett, and Teller (BET) surface area analysis, and transmission electron microscopy (TEM). Thermophysical property measurements were carried out at a temperature range of 40 and 60 °C. Based on the results, all particles were spherical and had an anatase structure with an average particle size ranging from 6 nm to 8 nm. There was also a monodisperse distribution in the base fluid. At the highest doping rate (0.3 %) and lowest mass concentration (0.3 %) of Ag-doped particles, the maximum specific heat (3051.31 J/kgK) of the study was observed. Increasing concentration resulted in a maximum 48.2 % decrease in specific heat for nanofluids containing 0.1 % Cu particles. The thermal conductivity increased by 2.40 % with doping but by only 1.89 % with concentration. The highest increase in viscosity was determined as 75.21 % at 40 °C, depending on the concentration increase. Thus, the doping method presents better heat transfer performance without an undesirable increase in viscosity compared to increasing the concentration.