Study on convective heat transfer and pressure drop of MWCNTs/water nanofluid in mini-tube

In recent times, the use of multi-walled carbon nanotubes (MWCNTs)/water nanofluids as a coolant has garnered immense interest due to their high thermal conductivity. Thus, this study investigates the effect of different mass fractions (${\phi }_{\text{w }}$) of MWCNTs (0.075, 0.125 and 0.25 mass%) on forced convection heat transfer. Uniform and stable nanofluids were prepared using the two-step method coupled with the addition of water-soluble polymer polyvinyl pyrrolidone (PVP) and using high-power probe sonicator. The test was carried out in a circular mini-tube (D_in = 1.1 mm), which was heated uniformly to study the developing and fully developed laminar flow. The Reynolds number (Re) varied from 200 to 500. The heat transfer coefficient was found to be significantly enhanced with increase in mass fraction of MWCNTs in the prepared nanofluid. The maximum enhancement of heat transfer coefficient was 23.9% for the nanofluid prepared with 0.25 mass% of MWCNTs. The experimental result revealed an increase in friction factor using the MWCNTs/water nanofluid. A maximum pressure drop of 9.9% was achieved for the highest mass fraction of MWCNTs.