English abstract
In the quest for higher performance and energy efficiency, nanofluids play a crucial role
in revolutionizing heat transfer processes. Their innovative properties offer enhanced
thermal management and sustainability across various applications. In this work, novel
nanofluids were prepared utilizing environmentally friendly nanoparticles made of
Powdered Activated Carbon supported Carbon Nanotubes (PAC-CNT) dispersed in a
base fluid made of a binary eutectic solvent consisting of ethylene glycol and imidazole.
Compared to traditional working fluids, this base fluid is distinguished by its thermal and
chemical stability and low vapor pressure. Six nanofluids were prepared with different
nanoparticle concentrations (0.08, 0.1, and 0.12 wt%). These were mechanically dispersed
in two systems of base fluids with 1:2 and 1:3 molar ratios of imidazole to ethylene glycol.
The stability of the nanofluids was tested by measuring their zeta potential. The
rheological behavior of the working fluids was determined at different shear rates. An
experimental investigation was conducted to find the effect of temperature, nanoparticles
concentration, and base fluid composition molar ratio on the thermophysical properties of
the base fluids and the nanofluids.
The lower base fluid ratio achieved less viscosity. The viscosity increments with adding
NPs were higher in nanofluids with the (1:3 IM:EG) system. There was a slight change in
density with the increasing nanoparticles load, and the density of all tested fluids
decreased with temperature. Determining the pumping requirement for nanofluids is also
essential for heat transfer applications. A model was used to estimate the pumping power
demand of the nanofluids by considering their rheological characteristics and their
measured density and viscosity. The interactions between the nanoparticles and the base fluid molecules affected the enhancement of the thermal properties of the nanofluids. The nanofluids containing 0.08 wt% of nanoparticles achieved a maximum enhancement in specific heat in both base fluid systems. These enhancements reached 10% and 44%,
respectively. The thermal conductivity (TC) was also enhanced by adding nanoparticles
to the base fluid. A remarkable 273% increase in TC was achieved with a nanoparticles
concentration of 0.08% in the first system (1:2 IM:EG). On the other hand, the
improvement in TC was lower in the second system as it reached 57% with 0.08 wt%
nanoparticles content. This research contributes valuable insights into the potential
applications of the studied nanofluids for enhanced heat transfer performance in various
engineering and industrial applications.
