Mixed convection of MWCNT–heat transfer oil nanofluid inside inclined plain and microfin tubes under laminar assisted flow

Abstract

This study describes an experimental investigation on the heat transfer characteristics of MWCNT (Multi walled Carbon Nano-tube)–heat transfer oil based nanofluid during mixed convection inside inclined plain and microfin copper tubes under uniform heat flux condition. Data were acquired for the laminar flow in the thermal entrance region and for tube inclination angles of 0, 45° and 90°. Pure heat transfer oil and nanofluids with nanoparticles weight concentrations of 0.05%, 0.1% and 0.2% were used as the working fluids. Effects of nanoparticles concentration, heat flux, tube inclination and free convection on the development of the thermal field are studied under buoyancy assisted flow condition for Grashof number, Reynolds number and Richardson number between 500 and 104, 10–100, and 0.1–10, respectively. Results show that Nusselt number increases slightly with an increase of nanoparticles weight concentration from 0 to 0.2% under a given Grashof number. Moreover, increasing Grashof number can raise the heat transfer coefficient in horizontal tube more than the inclined tubes under assisted flow condition. The effect of nanoparticles on heat transfer enhancement decreases by increasing of inclination and Richardson number, also, this effect is more pronounced in the plain tube rather than the microfin one.