Numerical Simulation of Tilted Obstacles Effect on the Water-Al2O3 Nanofluid Heat Transfer in the Internal Flow

In this research, a novel geometry consisting of a converging-diverging channel with three tilted obstacles is proposed to enhance the heat transfer of water-Al2O3 nanofluid in internal flow. Grid independence and validation have also been performed. The range of nanofluid volume fraction and Reynolds number are 0 <= phi <= 4% and 2 <= Re <= 300 respectively. Also, the range of the obstacle length and obstacle angle are 0.1 <= L/D-in <= 0.5 and 5(o )<= theta <= 45(o) respectively. The effect of the Re, nanofluid volume fraction, length, and angle of obstacle is studied. Flow streamlines and contours of temperature, velocity, and pressure are also presented under different conditions. The results demonstrate that as the angle of the obstacle increases, the average Nusselt number increases linearly, and the highest friction factor of the system is 1.55 and occurs at the location of the last obstacle. Also, the highest Nusselt number in the system is Nu=21.8, which occurs for phi=4% at the first obstacle location. Additionally, the Nusselt number and friction factor show very little dependence on nanofluid volume fraction, with an approximately 6% difference in the average Nusselt number between phi=%4 and phi=%1. The most significant pressure drop occurs at the location of the last obstacle, where the fluid pressure decreases by 15%, 26%, and 59% for the first, second, and third obstacles, respectively. By defining the ratios of the average Nusselt number of the novel geometry to that of a plain tube (NNR) and the ratios of the friction factor of the novel geometry to that of a plain tube (FFR), it was revealed that for Re=5 and Re=100 a doubling of Reynolds number, increases NNR by %1.6 and %0.8, respectively. Also, with an increase in Reynolds number, NNR and FFR increase, and their rate of increase is much higher for Re <= 50 than for Re>50.