Abstract In this research, an experimental study was conducted to clarify the forced convective heat transfer coefficient and pressure drop of water-based nanofluid including multi-walled carbon nanotubes (MWCNT) flowing through a horizontal circular tube. In order to prepare a stable colloidal suspension in aqueous media, two methods of non-covalent and covalent functionalizations were used by gum Arabic (GA) and arginine (Arg), respectively. Both nanofluids of MWCNT-GA/water and MWCNT-Arg/water were prepared at concentrations of 0.1 and 0.2 wt%, and they were investigated in a laminar regime (Re = 800–2000) at constant heat flux. A significant increase in the convective heat transfer coefficient with the addition of the Arg-functionalized MWCNT was the main achievement. Also, the convective heat transfer coefficient increased with increasing the nanofluid concentration and Reynolds number. Note that the thermal performance of MWCNT-Arg/water nanofluid is better than MWCNT-GA/water nanofluid. In addition, the low weight concentration of MWCNT had an insignificant effect on the pressure drop enhancement. Performance index results also showed that both prepared nanofluids are appropriate alternative for heat transfer equipment.

Keywords