An experimental study on heat transfer and pressure drop of MWCNT-water nano-fluid inside horizontal coiled wire inserted tube

An experimental investigation has been carried out to study the heat transfer and pressure drop characteristics of Nanofluid turbulent flow inside horizontal copper tube with different wire coil inserts under constant heat flux. The plain and coil inserted tubes were used as the test section's geometries and were heated by an electrical coil heater to produce constant heat fluxes. Nanofluids with different particle weight concentrations of 0.05%, 0.1%, and 0.2% were prepared by dispersion of functionalized multi-walled carbon nanotubes (MWCNTs) in distilled water and stabilized by means of an ultrasonic device. The effect of different parameters such as Reynolds number, nano-particle concentration, wire diameter and coil pitch on heat transfer coefficient and pressure drop are studied. Observations clearly show that for a specific nanoparticle concentration, increase in both heat transfer and pressure drop is obtained by inserting coil wires. In average, 85% increase in heat transfer coefficient and 475% penalty in pressure drop was observed at the highest Reynolds number inside the wire coil inserted tube with the highest wire diameter. Finally, two new correlations are introduced using the results of the experiments for predicting the Nusselt number and friction factor of the nanofluid flow inside coiled wires inserted tubes. (C) 2015 Elsevier Ltd. All rights reserved.