Heat transfer characteristics and pressure drop of COOH-functionalized DWCNTs/water nanofluid in turbulent flow at low concentrations

In this paper, an experimental study is performed to assess the heat transfer characteristics and pressure drop of low concentrations of a new class of nanotubes, i.e. COOH-functionalized double-walled carbon nanotubes (DWCNTs) suspended in water under turbulent flow in a double tube heat exchanger. First, the thermal conductivity and viscosity of nanofluids at volume fractions of 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, and 0.4% are measured and corresponding correlations are presented. Next, the heat transfer and pressure drop of the nanofluids through the double tube heat exchanger are evaluated. The results indicate that even the use of low concentration of the nanofluid, i.e. 0.4%, leads to a remarkable increase in heat transfer coefficient (by 32%) in comparison with the distilled water. On the other hand, the pressure drop due to using the volume fraction of 0.4% raised by 20%. Finally, analysis of the heat transfer and pressure drop data via thermal performance factor reveals that in spite of the pressure drop penalty, the COOH-functionalized DWCNTs/water nanofluid with volume fraction of 0.4% is a good option to use in the double tube heat exchanger.