An empirical study on fluid properties and pressure drop of nanofluid flow inside inclined smooth and microfin tubes

Fluid properties, pressure drop and friction factor of MWCNT (multi-walled carbon nanotube)–oil nanofluid for laminar assisting mixed convection was investigated experimentally. Smooth and microfin tubes were used as the test tubes under constant heat flux boundary conditions. Pure heat transfer oil and nanofluids with particle weight concentrations of 0.05%, 0.1% and 0.2% were utilized as the working fluids. Experiments were performed at θ = 0, 45 and 90° for the upward flow and Richardson number ranging from 0.1 to 10. Results showed that pressure drop increased as inclination was increased from 0 to 90°, 58, 2014, 176-183, but it decreased by increasing Grashof number, 58, 2014, 176-183. Moreover, experimental results indicate that effect of addition of nanoparticles to the base fluid doesn't have a notable effect on both pressure drop and friction factor. Also, pressure drop is more pronounced in microfin tube than the smooth one, thus, considering the penalty of pressure drop, utilizing the nanofluid in smooth tube at higher Richardson numbers is an efficient way in thermal applications. Finally, a new correlation was developed to calculate the skin friction coefficient in different inclinations and nanoparticle weight fractions.