Background: Hybrid nanofluids are considered as an extension of conventional nanofluids
which are prepared through suspending two or more nanoparticles in the base fluids. Previous
studies on hybrid nanofluids have measured their thermal conductivity overlooking other thermophysical
properties such as viscosity and electrical conductivity.
Objective: An experimental investigation is undertaken to measure thermal conductivity, viscosity,
and electrical conductivity of a hybrid nanofluid prepared through dispersing alumina nanoparticles
and multiwall carbon nanotubes in saltwater. These properties are the main important factors that
must be assessed before performance analysis for industrial applications.
Methods: The experimental data were collected for different values of the nanoparticle volume fraction,
temperature, salt concentration, and pH value. Attention was paid to explore the consequences
of these parameters on the nanofluid’s properties and to find optimal conditions to achieve the highest
value of the thermal conductivity and the lowest values of the electrical conductivity and the viscosity.
Results: The results demonstrate that although the impacts of the pH value and the nanoparticle volume
fraction on the nanofluid’s thermophysical properties are not monotonic, optimal conditions for
each of the properties are reachable. It is found that the inclusion of the salt in the base fluid may not
change the thermal conductivity noticeably. However, a considerable reduction in the viscosity and
substantial elevation in the electrical conductivity occur with an increase in the salt concentration.
Conclusion: With the addition of salt to a base fluid, the thermophysical properties of a nanofluid
can be controlled.