**Author details**

*Advances in Microfluidics and Nanofluids*

engineering applications including cooling [26–28].

research and development can be seen from **Figure 5**.

Portugal through grant- PTDC/NAN-MAT/29989/2017.

**4. Remarks**

important technologies.

**Acknowledgements**

Besides intensified research on various areas particularly on thermophysical properties and in several applications, research has been expanded to other new types of nanofluids like hybrid nanofluids and ionanocolloids (INC). Although research efforts on hybrid nanofluids have recently received increasing attention from researchers and findings from literature showed similar or better thermophysical properties compared to conventional nanofluids [24, 25], it is too early to explicitly identify their potential applications and benefits. On the other hand, ionanocolloids (suspensions of nanoparticles in ionic liquid) is another new type nanofluids which is in its early stage of research. However, ionanocolloids were found to exhibit superior thermal properties and show great potential compared to pure ionic liquids for many

Regarding research on thermophysical and heat transfer features, thermal conductivity is dominating the research producing more scattered data. However, the real mechanisms for the enhanced thermal conductivity of nanofluids are still inconclusive. Although many research efforts have been devoted until 2015 for the development of models for the prediction of thermal conductivity of nanofluids, the efforts have been declined recently despite no widely accepted models are available. This is due to the fact that no progress has been made on new mechanisms or physics-based understanding of underlying mechanisms. Nonetheless, despite above-mentioned impacts, potential applications, except few areas progressing on nanofluids towards developing them for real world applications are rather slow. Nanofluids also possess serious challenges which impede their real progress towards application and human benefits. A list of main challenges of nanofluids

This chapter gives an overview of progress, potential applications and main challenges of these two emerging and hugely important technologies. First it briefly discusses advancement of research and market values of microfluidics' followed by highlighting their main field of applications. Then, progress of and issues of nanofluids research and development is summarized besides bringing out potential application and challenges of this new class of popular fluids. This book is believed to be a useful reference source of information and knowledge in these two hugely

This work was supported by the Fundação para a Ciência e a Tecnologia (FCT),

**6**

S.M. Sohel Murshed Department of Mechanical Engineering, Center for Innovation, Technology and Policy Research (IN+), Instituto Superior Tecnico, University of Lisbon, Lisbon, Portugal

\*Address all correspondence to: smurshed@tecnico.ulisboa.pt

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
