Heat transfer enhancement of nanofluids using iron nanoparticles decorated carbon nanotubes

Abstract

Enhancing heat transfer in thermal fluid systems can contribute significantly towards the improvement of thermal efficiency resulting in reducing energy consumption and hence carbon emission. Conventional fluids like water and oil have limited heat transfer potential. The need for the development of new classes of fluids with enhanced heat transfer properties is thus becoming essential. Many studies have developed nanofluids using nanoparticles, however, they showed a limited enhancement in heat transfer. This study investigated the heat capacity, enhancement of heat transfer, viscosity, and pressure drop of nanofluids with carbon nanotubes (CNTs) and CNTs doped with iron oxide nanoparticles (Fe2O3-CNT). The surfaces of carbon nanotubes were doped with 1 wt.% and 10.0 wt.% iron oxide nanoparticles. The pristine and doped CNTs were used to prepare heat-exchange nanofluids with additive concentrations of 0.01, 0.05, and 0.10 wt.%. A shell and tube heat exchanger was used to evaluate the overall heat transfer coefficient and the associated pressure. The specific heat capacity of the nanofluids was measured by differential scanning calorimetry (DSC). The results showed that the specific heat capacity of the nanofluids with undoped and doped CNTs is significantly higher than that of pure water by about 10% and 55%, respectively. The heat transfer rate of the nanofluids increased sharply with the CNT dosage the iron nanoparticles loading and reached up to 55% enhancement with doped CNTs. We observed that the power required to exchange 1.8 kW heat using nanofluid containing 0.1 wt.% of 10 wt.% Fe2O3-CNTs was 20 times lower than the power required to exchange the same amount of heat using water. This is because the iron nanoparticles enhanced the dispersion of the CNTs and increased their heat capacity and thermal conductivity. Compared with that of pure water, the encountered pressure drop of the nanofluid at the same flow rate was almost unchanged, resulting in no extra pumping energy penalty.