Thermal Convection in Nanofluids

Abstract

Nanofluids consist of a stable suspension of very small metallic or metallic-like particles suspended in a carrier fluid. The particles are called nanoparticles and the stability of the suspension and prevention of particle settlement has been achieved in the laboratory. There are many types of nanofluids but typical examples might involve a suspension of copper, Cu, copper oxide, CuO, or aluminium oxide, Al$_2$O$_3$, in water or ethylene glycol. Other types of nanofluids are made by suspending carbon nanotubes in an appropriate oil. Research on nanofluids and their use in heat transfer devices is very much in vogue in the engineering and industrial communities. One reason for this is that nanofluids appear to have highly desirable properties for greatly increasing heat transfer by comparison with ordinary fluids. Thermal conductivities of metals like copper, or their oxides, are usually much greater than those of a typical carrier fluid. Because of this the nanofluid suspension may have an increased thermal conductivity over that of the pure fluid, although the effects of changes to both the thermal conductivity and the viscosity should be considered together. One belief is that an increased thermal conductivity may have a pronounced effect on heat transfer. In this chapter we review some recent work on models to describe the behaviour of a nanofluid. We also present work on hyperbolic thermal convection in a fluid. The effects of slip boundary conditions in a nanofluid are stressed. In addition, a model is presented where the nanofluid suspension employs a non-Newtonian constitutive theory to allow for a non-parabolic flow profile in fluid movement in a channel.