EXPERIMENTAL INVESTIGATION OF CONVECTIVE HEAT TRANSFER OF SINGLE AND MULTI-WALLED CARBON NANOTUBES/WATER FLOW INSIDE HELICAL ANNULI
Farzad Fathian, Seyed Ali Agha Mirjalily, Mohammad Reza Salimpour, Seyed Amir Abbas Oloomi
Abstract
The aim of the present investigation is to study the effect of adding single-walled and multi-walled carbon nanotubes to distilled water upon the heat transfer characteristics of the flow in helical annuli. The helical annulus is formed by twisting a straight double-tube heat exchanger. The outer surface of the helical annulus is adiabatic, while a hot fluid goes through the core helical tube providing heat source for heating the cool fluid passing through the annulus. Three double-tube coils with annulus curvature ratios of 0.0375, 0.071, and 0.123 are prepared and tested to assess the effect of the coil geometry on the heat transfer. Other parameters, such as Reynolds number, nanofluid volume fraction, and the type of carbon nanotubes are investigated, as well. Based on the experimental data, the nanofluid flow shows much higher Nusselt numbers compared to the base fluid flow. Finally, to predict the Nusselt number, a correlation is proposed using least-square method where a reasonable agreement is observed between the predicted Nusselt numbers and the experimental counterparts.