Rheological characterization of nanofluids

Vigorous research on to the approaches that have to be made to enhance heat transfer and rheological properties of fluids has led to the evolution of nanofluids. Nanofluids are colloids that are produced by suspending nanoparticles of metals/nonmetals having size ranging from 1nm to 100nm in a suitable base fluid. Nanofluids unlike other conventional fluids have superior thermal conductivity, which made them remarkably suitable for applications involving heat transfer. The major thermophysical parameter that governs the heat transfer properties of a nanofluid is its viscosity because it is highly responsive to changes in temperature. This chapter covers the effective parameters that can affect the viscosity of nanofluids and their cross correlations. The rheological behavior of the nanofluid when adding different nanoparticles is also analyzed and compared with the help of available literature. Through a comprehensive review of the findings from these research groups, by analyzing their approaches and outcomes, we can figure out the present research anomalies and challenges. For advanced heat transfer applications of nanofluids, researchers may hence choose the suitable nanoparticle and base fluid, along with the best thermodynamic conditions in which the nanofluid exhibits the desirable rheological behavior of shear viscosity, yield stress, etc. The summary of research works conducted by investigators worldwide as discussed in this chapter involves the effects of the type, shape, and volumetric concentrations of the nanoparticle used, the addition of surfactants, shear rate, etc. which are the dominant factors determining the rheological behavior of the nanofluids and thus their heat transfer properties.