Heat transfer and pressure drop of nanofluids containing carbon nanotubes in laminar flows

The heat transfer and pressure drop of nanofluids containing carbon nanotubes in a horizontal circular tube are experimentally investigated. The friction factor of the dilute nanofluids shows a good agreement with the prediction from the Hagen-Poiseuille flow theory. A considerable enhancement in the average convective heat transfer is also observed compared with the distilled water. For the nanofluids with volumetric concentration of 0.05% and 0.24%, the heat transfer enhancement are 70% and 190% at Reynolds number of about 120 respectively, while the enhancement of thermal conductivity is less than 10%, therefore, the large heat transfer increase cannot be solely attributed to the enhanced thermal conductivity. By measuring the pump power supply and the thermal conductance of the test tube, our results suggest that the nanofluids at low concentration enhance the heat transfer with little extra penalty in pump power, thus have great potential for applications in the heat transfer systems. (C) 2012 Elsevier Inc. All rights reserved.