Numerical and experimental investigation on heat transfer characteristics of nanofluids in a circular tube with CDTE

This paper reported numerical simulation investigations on heat transfer performance of ZrO2-water and Cu-water nanofluids in the tube with concentric double twisted element(CDTE)(Re = 6000-12000). Furthermore, experiments verified that the two-phase flow model method was more suitable for the numerical simulation of nanofluids in the tube with CDTE. The Nusselt numbers with CDTE and nanofluids obviously increased and also showed a positive correlation with the nanofluid concentration. The Nusselt numbers of Cu-water nanofluid were better than ZrO2-water nanofluid. While the friction factor(f ) of CDTE tube between the nanofluids increased little, the maximum difference was only 3.23%. The heat transfer performance was evaluated by performance evaluation criteria (PEC), cross-section entransy efficiency(psi(c)) and radial-flow(RF) number. The heat transfer performance of Cu-water nanofluids was all superior to ZrO2-water nanofluids. The PEC values in nanofluids increased with increasing concentration. The maximum PEC value was 1.96 in 1% Cu-water nanofluid. Subsequently, the psi(c) of CDTE tube increased with the increase of cross-section position and nanofluid concentration. The maximum psi(c) was 91.22% in 1% Cu-water nanofluid at Re= 6000. When an appropriate concentration of nanofluids was used and the nanofluid was passed through the CDTE, the RF numbers increased obviously. The maximum RF number was 0.1028 with 0.5% Cu-water nanofluid at Re= 6000.