Hybrid nanofluids are synthesized by suspending dissimilar nanoparticles either in a mixture or composite form in the base fluid. Hybrid nanofluids of silica-multi walled nanotube in water could be synthesized using wet chemical method. The nanofluid viscosity formula was first developed by A. Einstein in 1906, and the model was based on the assumption that the viscous fluid contains spherical particles at a very low volume fraction. One of the most significant thermophysical properties to study the capability of nanofluids in heat transfer area is its thermal conductivity. The dispersion methods used for synthesizing nanofluids affect the stability as well as the thermal conductivity of nanofluids. The pressure drop and pumping power in engineering applications also depend upon the density of nanofluids. Significant energy savings and reduction in emissions can be achieved through the use of nanofluids in industrial cooling. The stability of nanocomposite particles in the base fluid is a major challenge in the synthesis of hybrid nanofluids. © 2022 Elsevier B.V., All rights reserved.