Heat Transfer and Friction Factor of Al2O3 Nanofluid Flow in a Double Pipe U-Tube Heat Exchanger and with Longitudinal Strip Inserts: An Experimental Study

Heat transfer and friction factor of Al2O3 nanofluid flow in a double pipe U-tube heat exchanger fitted with longitudinal strip inserts are estimated experimentally. Nanofluid is circulated inside the tube and hot water is circulated in the annulus of double pipe U-tube heat exchanger. The experimental data is generated with water and nanofluid in the Reynolds number range of 3000 to 30000, in the volume concentration ranging from 0 to 0.03% and longitudinal strip inserts of aspect ratios 1, 2, 4 and 12. The results indicates that the Nusselt number and friction factor of entire pipes for 0.03% concentration of nanofluid with longitudinal strip inserts of aspect ratio 1 enhances by 47.35% and 1.21 times compared to water. However, the pressure drop in the pipe increases with the increases of nanoparticle volume concentration and aspect ratio of the inserts. The empirical correlations for the Nusselt number and friction factor are obtained as functions of the Reynolds number, Prandtl number, volume concentration and aspect ratio.