ABSTRACT
Despite the fact that nanofluids have received an explosion of research interest in the recent years, the real progress of this not-so-old field has been notably impeded due to a number of research shortcomings and challenges that researchers have yet to overcome. One of such challenges is the preparation of long-term stable nanofluids, which is crucial for their sustainable applications. Another critical issue of nanofluids research and development is the lack of accurate measurements of its properties and characteristics such as effective thermal conductivity and convective heat transfer coefficients. This chapter mainly focuses on these key issues of nanofluids. Besides providing critical analysis and discussion on nanofluid preparation, stability evaluation, and thermophysical properties, it critically reviews studies on flow and convective heat transfer of nanofluids in microchannels and cavities and it emphasizes the role of accurate measurements of key parameters related to convective thermal transport and flow performance. It is demonstrated in this study that despite the significant increase in thermophysical properties as well as convective heat transfer (cooling) performance of nanofluids in those geometries, the literature data are quite scattered and no well-accepted factors or mechanisms behind such anomalous results are yet elucidated. In addition, neither classical nor recent empirical co-relations/models are also found capable of predicting the properties and heat transfer coefficient of nanofluids.
