Heat and mass transfer characteristics of carbon nanotube nanofluids: A review

The pursuit of superior working fluids for heat and mass transfer systems in the industry is on the rise, inspired by not only to maximize revenue but also to accommodate heat dissipation or chemical separation under extreme conditions. The addition of a small amount of nanoparticle, a product called nanofluid, has been initiated over the last decade. In particular, researchers have employed carbon nanotubes (CNTs) into conventional fluids as their preferred nanoparticles due to the merits of having a remarkable thermal conductivity compared to other nanoparticles. Here, we present a comprehensive and up to date review of this incredible fluid being applied in various heat transfer (convective and boiling) and mass transfer systems such as heat exchangers and separators. Other critical parameters associated with the practicality of the CNT nanofluids such as pumping power and efficiency are also discussed. We surveyed a remarkable range of results of some of the heat and mass transfer studies that strongly depend on the inherent CNT nanofluid characteristics and operating conditions such as CNT treatment, size, concentration, Reynolds number, and so on. A major conclusion that can be drawn from this review is the significantly higher heat transfer coefficient at lower pressure drop or pumping power of the CNT nanofluid compared to other nanofluids, which implied better thermal performance of the heat transfer system. Besides that, the concentration of CNT is the influential factor to achieve optimum boiling heat transfer while the mass transfer performance of the CNT nanofluid is moderately good against other nanofluids. Additionally, CNT treatment using covalent functionalization is crucial for the overall stability and performance of the CNT nanofluid. However, several issues that inhibit their widespread use such as possible corrosion-erosion in systems, lack of risk assessments, and high cost of CNT nanofluid must be thoroughly addressed in future studies.