Preparation Techniques of TiO2 Nanofluids and Challenges: A Review

Abstract

Titanium dioxide (TiO 2 ) has been used extensively because of its unique thermal and electric properties. Different techniques have been used for the preparation of TiO 2 nanofluids which include single-step and two-step methods. In the natural world, TiO 2 exists in three different crystalline forms as anatase, brookite, and rutile. Nanoparticles are not used directly in many heat transfer applications, and this provides a major challenge to researchers to advance towards stable nanofluid preparation methods. The primary step involved in the preparation of nanofluid is the production of nano-sized solid particles by using a suitable technique, and then these particles are dispersed into base fluids like oil, water, paraffin oil or ethylene glycol. However, nanofluid can also be prepared directly by using a liquid chemical method or vapor deposition technique (VDT). Nanofluids are mostly used in heat transfer applications and the size and cost of the heat transfer device depend upon the working fluid properties, thus, in the past decade scientists have made great efforts to formulate stable and cost-effective nanofluids with enhanced thermophysical properties. This review focuses on the different synthesis techniques and important physical properties (thermal conductivity and viscosity) that need to be considered very carefully during the preparation of TiO 2 nanofluids for desired applications.

Effects of Nanoparticles Materials on Heat Transfer in Electro-Insulating Liquids

“…As is known from the literature, one of the main difficulties associated with the preparation of stable electro-insulating nanofluids is the fact that nanoparticles are hard-soluble compounds, or insoluble in base liquids [33,61]. It is difficult to obtain a stable dispersion of nanoparticles in electro-insulating liquids.…”

“…Recently, an increasing amount of research related to the search for alternative electro-insulating liquids has focused on the use of nanotechnology [31]. By dispersing nanometric materials (nanoparticles, nanofibers, nanotubes, nonowires, nonorods, nonosheets) in base fluids, a new class of dielectric liquids called nanofluids can be obtained [32,33]. Choi invented this term in 1995 [34].…”

Preparation and characterization of N-doped TiO2/C composite

“…Galstyan et al illustrated the gas-sensors application of TiO 2 fabricated using physical and chemical methods [13]. Ali et al illustrated the preparation methods of TiO 2 including one-step and two-step, and focused on the application of TiO 2 nanofluids in heat transfer [14].…”

Mixed convection heat transfer and entropy generation analysis of copper–water nanofluid in a vertical channel with non-uniform heating

“…Numbers of review articles have also been published covering the methods of preparation, the characterization, the modeling and the application areas (e.g. [6][7][8][9]). They concluded that more research is required to simplify the methods of preparation of nanofluids in order to make them cost effective.…”