Experimental investigation on enhancement of heat transfer using Al2O3/water nanofluid in a u-tube with twisted tape inserts

An investigation is made experimentally with an attempt to enhance the rate of heat transfer of Al2O3 nanofluid in a U-tube heat exchanger with twisted tape insert. The heat transfer coefficients and the corresponding friction factors needed for performance analysis are determined at variable operating conditions of the heat exchangers with particle volume concentration of 0.01% and 0.03% and twist ratios ranging between 5 and 20. Experimental data are obtained at flow rates ranging from 0.0333 to 0.2667 kg/s and Reynolds number ranging from 3000 to 30,000. The Nusselt number of entire pipes for 0.03% concentrations of nanofluid with twisted tape inserts is enhanced by 31.28% compared to water while the friction factor is increased by 1.23 times compared to water with twisted tape insert of H/D = 5. Correlations are developed to estimate the Nusselt number and friction factor. The results of the investigation indicated significant improvement in the performance parameters of the heat exchanger with a rise in volume concentration of the nanoparticle.