Numerical investigation of turbulent nanofluid flow behavior in a multi-stream plate-fin heat exchanger with a novel design of fractal fins

Abstract

Plate heat exchangers are widely used in various industries. This study considers using a novel design of fractal shape fins with a new structure on the performance of multi-stream plate-fin heat exchangers for the first time, which has not been studied by researchers before. The numerical study is done with a 3D finite volume method. The effect of using Oil/MWCNT nanofluid and using various configurations of fractal fins with different attack angles ranging from 30 degrees to 100 degrees with the range of Reynolds number of 10,000–40,000, have been studied in the current research. These changing parameters have a significant impact on the flow field and heat transfer in the heat exchanger. The results of this study show that increasing the angle of attack of fractal fins creates more flow deflection and higher fluid mixing. The rise of the Reynolds number creates stronger vortexes as the flow passes over the fins, thereby it can augment the fluid mixing in the areas which are close to the finned. As the Reynolds number rises, the growth of the thermal boundary layer diminished. It can also be seen that as the fluid impacts the fractal fins at higher angles of attack, the temperature distribution becomes more uniform in the heat exchanger. Increasing the Reynolds number from 10,000 to 40,000 increases the heat transfers up to 63 %. At the constant Reynolds numbers, increasing the fraction of solid nanoparticle volume up to 4 % in the cooling fluid augment the heat transfer rate by 48 % compared to the base fluid. Increasing the fluid velocity results the amplification of longitudinal vortex formation. Therefore, the pressure loss is higher at the increased Reynolds numbers. At the lower Reynolds numbers, the pumping power has a weaker dependency on the nanofluids concentration. Increasing the angle of attack of fractal fins increases the pumping power by 50 % compared with the angle of attack of 30 degrees. Increasing the fractal fin angle of attack compared with 30 degrees increases friction by 45–85 %. Changes in the Colburn factor show that considering all parameters that increase heat transfer, the Colburn factor increases by 23–42 % compared with the base scenario with Re = 10,000 and angle of attack = 30 degrees.