**3. Overviewing nanofluids progress and challenges**

The advancement in thermal management of modern equipment and systems are greatly impeded due to the limited cooling capabilities of conventional heat transfer fluids. Thus, there is an urgent need for heat transfer fluids with improved thermal properties and features. Nanofluids having found considerably higher heat transfer properties and features such as thermal conductivity, convective and boiling heat transfer compared to their base conventional fluids are believed to be capable of meeting such high cooling demands [8, 17–22]. With great features and properties nanofluids can be used for increased heat transfer and many other important fields of applications such as transportations (engine cooling or vehicle thermal management), microelectronics, solar energy technologies, micro-electromechanical systems (MEMS), electronics and instrumentations, heat exchangers, heating-ventilating and air-conditioning (HVAC), cooling electronics, microfluidics, defense, medical and so on (**Figure 4**). Researchers have also focused on studying nanofluids in diverse applications like- advanced cooling technologies, heat pipes, solar energy conversion and harvesting [8, 19, 23]. Being a multidisciplinary field and having numerous potential applications the impacts of nanofluids are very high. Although there are no recent market analysis or data for nanofluids, an estimation of the potential worldwide market for nanofluids was made sometimes ago and it was estimated to be over 2 B dollars per year only in heat transfer applications [21]. Majority of this market value came from cooling applications and

**5**

**Figure 5.**

*Some key challenges of nanofluids.*

**Figure 4.**

*Applications of nanofluids.*

*Introductory Chapter: An Overview of Advances in Microfluidics and Nanofluids Technologies*

nanoparticles (main component of nanofluids). Although extensive research works have been performed particularly during the past decade, nanofluids real applications and benefits are not yet achieved. Thus, more systematic and care-

*DOI: http://dx.doi.org/10.5772/intechopen.98425*

ful research works on nanofluids are still necessary.

*Introductory Chapter: An Overview of Advances in Microfluidics and Nanofluids Technologies DOI: http://dx.doi.org/10.5772/intechopen.98425*

nanoparticles (main component of nanofluids). Although extensive research works have been performed particularly during the past decade, nanofluids real applications and benefits are not yet achieved. Thus, more systematic and careful research works on nanofluids are still necessary.

**Figure 4.** *Applications of nanofluids.*

*Advances in Microfluidics and Nanofluids*

nanoparticles in aqueous fluid, depth of microchannel and flow rate on the droplet formation and size manipulation were investigated [10, 11, 16]. Although results are interesting and reveal the potential of nanofluids in microfluidics, more extensive

The advancement in thermal management of modern equipment and systems are greatly impeded due to the limited cooling capabilities of conventional heat transfer fluids. Thus, there is an urgent need for heat transfer fluids with improved thermal properties and features. Nanofluids having found considerably higher heat transfer properties and features such as thermal conductivity, convective and boiling heat transfer compared to their base conventional fluids are believed to be capable of meeting such high cooling demands [8, 17–22]. With great features and properties nanofluids can be used for increased heat transfer and many other important fields of applications such as transportations (engine cooling or vehicle thermal management), microelectronics, solar energy technologies, micro-electromechanical systems (MEMS), electronics and instrumentations, heat exchangers, heating-ventilating and air-conditioning (HVAC), cooling electronics, microfluidics, defense, medical and so on (**Figure 4**). Researchers have also focused on studying nanofluids in diverse applications like- advanced cooling technologies, heat pipes, solar energy conversion and harvesting [8, 19, 23]. Being a multidisciplinary field and having numerous potential applications the impacts of nanofluids are very high. Although there are no recent market analysis or data for nanofluids, an estimation of the potential worldwide market for nanofluids was made sometimes ago and it was estimated to be over 2 B dollars per year only in heat transfer applications [21]. Majority of this market value came from cooling applications and

research needs to be performed in this new combined field.

**3. Overviewing nanofluids progress and challenges**

**4**

**Figure 3.**

*Applications of microfluidic technology.*

**Figure 5.** *Some key challenges of nanofluids.*

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 engineering applications including cooling [26–28].

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