Numerical study on heat transfer and flow characteristics of nanofluids in a circular tube with trapezoid ribs

This study aims to investigate heat transfer and flow characteristics of ethylene glycol/water (EGW) and CuO-EGW nanofluids in circular tubes with and without trapezoid ribs. Nusselt number and friction factor in tubes with trapezoid ribs are analysed under a constant heat flux by changing rib bottom angles. This study compares the convective heat transfer coefficients of 6 vol.% CuO-EGW nanofluid and base fluid. It is found that under a constant Reynolds number, the Nusselt number and friction factor for CuO-EGW nanofluid and base fluid increase with an increase in the inclination angle. The Nusselt number for the CuO-EGW nanofluid in the tube with 75 degrees rib bottom angle averagely increases by 135.8% compared to that in the smooth tube, and the performance evaluation criterion is 1.64.