Chapter 3 - Thermophysical and rheological properties of hybrid nanofluids

Abstract

Enhancing the heat transfer rate between the working fluids is the most critical aim for the majority of thermal systems because an increase in heat transfer rate will improve the overall efficiency of the system. Design of the thermal system and choice of the working fluids to be used within the system are the two key factors that should be engineered for improved efficiency of thermal systems. For that reason, the thermophysical properties of the working fluids need to be studied accurately to be able to choose the best option. Pure fluids and their nanoparticle blends are two popular options to be used as working fluids. A nanofluid is defined as a fluid that contains nanoparticles, that is, nanometer-sized particles. A hybrid nanofluid, on the other hand, is a nanofluid composed of two or more nanomaterials. Adding nanoparticles to base fluids has been shown to significantly enhance heat transfer characteristics of base fluids such as water and ethylene glycol. In this chapter, the thermophysical and rheological properties of hybrid nanofluids are studied in detail. This chapter begins by exploring measurement techniques used in quantifying the thermophysical and rheological properties of hybrid nanofluids. Then, the chapter analyzes theoretical and experimental results related to the thermophysical and rheological properties of hybrid nanofluids. This chapter further discloses and compares important characteristics of different hybrid nanofluids, such as thermal conductivity, viscosity, heat capacity, density, and wetting. Furthermore thermophysical and rheological properties of hybrid nanofluids are characterized in the chapter based on particle concentration, particle composition, particle shape, particle size, the base fluid type, and the temperature. Moreover, the chapter compares hybrid nanofluids with unitary nanofluids with regards to their thermophysical and rheological properties. Finally the chapter closes with a discussion of current challenges and new directions in the field.