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The viscosity of nanofluids, and consequently their energy dissipation, is a challenging factor in real applications because it affects the pressure drop and pumping power of equipment in industries. The aim of this experimental and simulation study is to measure and calculate the viscosity of a carbon nanotube (CNT)− water nanofluid by employing a rotational viscometer and by molecular dynamics (MD) simulation. The effects of temperature, solid concentration, and CNT diameter on the dynamic viscosity were examined within the temperature and volume concentration ranges of 25−65 °C and 0.125%−1%, respectively. Interestingly, the maximum observed increase in the relative viscosity of CNT−water nanofluid occurred at 65 °C, whereas the absolute viscosity of the nanofluid was minimum at this temperature. It was further found that the dynamic viscosity increases with increasing volume fraction of nanoparticles and with decreasing nanofluid temperature, whereas changing the diameter of the CNT does not have a significant effect on nanofluid viscosity. Furthermore, a correlation function was proposed in terms of solid concentration and nanofluid temperatures based on the MD simulation results, and its accuracy was investigated by analyzing the margin of deviation. The findings of this study are useful for industrial applications of CNT/water nanofluids.

Heat transfer at the liquid/solid interface, especially at the nanoscale, has enormous importance in nanofluids. This study investigates liquid/solid interfacial thermal resistance and structure of the formed molecular nanolayer around a carbon-based nanoparticle. Employing non-equilibrium molecular dynamics simulation and thermal relaxation method, the nanofluid systems with different nanoparticle diameters and different surface wettability were investigated. Simulation results show that carbon nanotubes (CNTs) with a smaller diameter attract more value of the base fluid and lead to a reduced Kapitza resistance. It was found that the thickness of the nanolayer around the nanoparticle is independent of the water/carbon interaction strength. Also, the value of the Kapitza resistance decreases with increasing the interaction strength. Ultimately, a correlation was proposed for the thermal resistance of CNT/water and graphene/water nanofluids in terms of wettability intensity of nanoparticle surface.The proposed correlation in addition to fitting to simulation results can cover the physical conditions of the system.Corresponding authors: * Rajabpour@eng.ikiu.ac.ir † s_sadodin@semnan.ac.ir

Single-phase La-substituted bismuth ferrite (Bi 1−x La x FeO 3) nanoparticles have been synthesized by thermal decomposition of a glyoxylate precursor. The crystal structure transition of BiFeO 3 from the rhombohedral (R3c) to the cubic P m3m structure by La addition was confirmed by X-ray diffraction and infrared spectrometry methods. Furthermore, the Bi 1−x La x FeO 3 nanoparticles showed a weak ferrimagnetism behaviour, while the magnetization increased from 0.18 to 0.48 emu g −1 with La substitution. The Bi 1−x La x FeO 3 nanoparticles exhibited strong absorption in the visible region with the optical band gap calculated from Tauc's plot in the range of 2.19-2.15 eV. Furthermore, the effects of La substitution on the photodegradation of the methylene blue (MB) under visible light were also studied. The photodegradation of MB dye was enhanced from 64 to ∼99% with increasing La substitution from x = 0 to 0.1 and then decreased to 8% for x = 0.15.