Forced convection of Al2O3/water nanofluids with simple and modified spiral tape inserts

Present study investigates experimentally the heat transfer and pressure drop characteristics of Al2O3/water nanofluids with particle concentration ranging from 0.025 to 0.1 vol%. Two types of inserts are used in the present research, simple spiral tape (SST) and modified zig-zag cut spiral tape (MST). The Reynolds number range employed in the present study is 4300 to 39,000 with constant heat flux condition. Three twist ratios are analyzed for both simple and modified inserts: 5.65, 4.35 and 3.04. Simple spiral tape inserts are efficient to enhance the heat transfer but with the increase in penalty of pressure drop. With water as a working fluid, a 12.7% increase in heat transfer is observed using 5.65 twist ratio simple spiral tape insert. Thermal performance factor analysis shows that modified twisted tapes with twist ratios of 3.04 and 4.35 effectively enhance the heat transfer without extra penalty of pumping power. The correlations are developed for predicting the Nusselt number and friction factors for the simple and modified spiral tape inserts.