Heat Transfer Enhancement Using Nanofluids in a Circular Tube Fitted with Inserts

Abstract

A numerical investigation is performed to study the effects of different geometrical parameters and nanofluids on the thermal and flow fields through circular tubes fitted with inserts with Reynolds number ranging from 500 to 1750 and heat flux of 1000 W/m(2). The two dimensional continuity, Navier Stokes and energy equations are solved by using the finite volume method. The optimization through twisted tape with eleven types of tube having 20 mm inner diameter was studied by changing the dimensions of twisted tape such as the width ratio (W/D) in the range of 0.2-0.8 and the twist ratio (H/D) in the range of 2.5-4 for water as a working fluid to reach the optimal geometry with maximum performance evaluation criterion (PEC). The effects of using different types of nanoparticles such as Al2O3, CuO, SiO2, and ZnO, different nanoparticles volume fractions in the range of 1% to 4% and different nanoparticles diameters in the range of 25 nm to 80 nm in water base fluid were examined. The effects of different Reynolds numbers and the dispersion of nanoparticle in different types of base fluid such as ethylene glycol, engine oil and water in circular tube were also analyzed. Simulation results show that the Nusselt number increased as the width ratio and Reynolds number increased and twist ratio decreased. The highest Nusselt number was obtained with W/D = 0.8, while the efficient flow (max. PEC) was achieved with W/D = 0.7 for H/D = 2.5. The Nusselt number through the circular tubes with insert was enhanced with the increase of the particle volume fraction and with the decrease of nanoparticles diameter.