Since the past decade, rapid development in nanotechnology has produced several aspects for the scientists and technologists to look into. Nanofluid is one of the incredible outcomes of such advancement. Nanofluids (colloidal suspensions of metallic and nonmetallic nanoparticles in conventional base fluids) are best known for their remarkable change to enhanced heat transfer abilities. Earlier research work has already acutely focused on thermal conductivity of nanofluids. However, viscosity is another important property that needs the same attention due to its very crucial impact on heat transfer. Therefore, viscosity of nanofluids should be thoroughly investigated before use for practical heat transfer applications. In this contribution, a brief review on theoretical models is presented precisely. Furthermore, the effects of nanoparticles' shape and size, temperature, volume concentration, pH, etc. are organized together and reviewed.

Nanofluid, a simple product of nanotechnology has become a topic of attraction due to its extraordinary heat transfer performance in various areas including cooling, power generation, defense, nuclear, space, microelectronics and biomedical appliances. However, preparation and stabilization of such fluids are indeed a matter of concern for better understanding. For the last decade numerous research and development works have been done in the synthesis and stability of such materials. In this contribution, a brief review has been presented to provide an update about the preparation and stabilization methods of nanofluids.

Nanofluids are suspension of highly conductive nano‐sized particles in conventional fluids that may be applicable as ultrafast cooling agent to extend the thermal performance of cooling devices. However, before considering the feasibility as coolant for high heat flux components, a thorough investigation of the long‐term stability of nanofluids is of paramount importance. Preparation of extremely stable nanofluids has become one of the main technical challenges. The present contribution aims to summarize the recent developments in the preparation, characterization, and stabilization of nanofluids based on the information available in literatures. Lastly, existing needs and attainable solution to challenges, leading to the upcoming research in the development of highly stable nanofluids, are discussed.

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