Experimental and numerical investigation on turbulent flow of multiwall carbon nanotube-water nanofluid inside vertical coiled wire inserted tubes**

In this paper, heat transfer and pressure drop behavior of multiwall carbon nanotube-water nanofluid turbulent flow inside vertical coiled wire inserted tubes with constant heat flux boundary condition were investigated experimentally and numerically. In the experimental section, plain and five wire coils inserted tubes were used as the test sections geometries. In the numerical section, the governing equations associated with the required boundary conditions were solved using finite volume method based on the SIMPLE technique. The standard k-6 turbulence model was used in order to simulate the turbulence flow. The great agreement was found between the obtained experimental and numerical data with those predicted by the classical correlations for heat transfer and pressure drop in the plain tube. After validating the achieved data, the effects of various ranges of Reynolds number, particle weight concentration, wire diameter and coil pitch ratio on heat transfer coefficient and performance evaluation criterion were declared. It was concluded that the Nusselt number has been increased up to 102% at the highest Reynolds number inside the coil wire WC3. Moreover, the maximum enhanced performance evaluation criterion was seen for the wire coil with lowest coil pitch-to-tube inner diameter ratio (p/d) and highest wire-to-tube diameter ratio (e/d).