This article focuses on a comprehensive review in summarizing on the recent research developments regarding the theoretical and experimental investigations about the thermophysical characteristics of carbon nanotubes-nanofluids with mass concentration varying from 0.1 to 1wt% and at the temperatures of 10-60°C. Carbon nanotubes are promising new materials for their mechanical, electrical, thermal, optical and surface properties. The current study explores how several factors those strongly affecting thermal conductivity, viscosity, specific heat and density of carbon nanotube-nanofluids include particle concentration, temperature, particle size, particle type, particle shape, different base fluids, surfactant and ultrasonic time. In addition, different apposite models contributing augmentation of thermal conductivity and decaying of viscosity of carbon nanotubes-nanofluids are introduced. Further, significant heat transfer mechanisms namely Brownian motion, nanoclustering, thermophoresis, and interfacial nano-layer responsible for significant role in augmenting the heat transfer capabilities of carbon nanotubes-nanofluids are well discussed. The viscosity of SWCNT nanofluids shows a non-Newtonian shear-thinning behavior due to the alignment of nanotubes clusters and agglomerates with increasing shear rate. The results reveal that the thermal conductivity, viscosity and density of CNT-nanofluids are higher than that of the base fluid, and enhances with rise in nanotubes concentration. Specific heat peters out with rise in particle loadings and upgrades with increase in temperature. Thermal conductivity of CNT-nanofluids upsurges, whereas the viscosity and density of CNT-nanofluids diminish with rise in the temperature. Finally, the challenges for the future are conveyed.
KEYWORDS: Carbon Nanotubes Nanofluids, Nanoclustering, Interfacial nano-layer