Forced Convection Heat Transfer via Horizontal and Vertical Pipes Elbow-Shaped at Constant Heat Flux: A Numerical Analysis

In the present work, a numerical investigation has been executed for airflow behavior and heat transfer in steady state for three-dimensional flow through horizontal and vertical pipes with an elbow. The primary aim of this research is to identify the effect of six different velocities of air adopted (1.5 m/s, 2 m/s, 2.5 m/s, 3 m/s, 3.5 m/s, and 4 m/s) as inlet boundary condition on the thermal performance along pipes length. Airflow through steel pipe exposed to constant heat flux (1655.6 W/m2). Airflow is investigated by evaluating the distributions of velocity and pressure, whereas the thermal aspect is assessed through the analysis of the Nusselt number. The Finite Volume Method acted as the solver for the governing equations in a three-dimensional model. The study model's geometries and meshes were first created in ANSYS Workbench, followed by the execution of the relevant simulations using the FLUENT code. The results indicated that the increment temperature at pipe curvature for all velocity inlet values because local velocity is reduced in this region. At low air velocity inlet, temperature difference between wall pipe and fluid becomes high then a low average Nusselt number appears. However, at higher velocity of inlet, it becomes low and as a result Nusselt number increases. In addition, at elbow curvature had a considerable effect on the air velocity, the velocity value at the outer elbow side was higher than at the inner elbow side. These changes in velocity profile happen due to stagnation region that emerges on the inner side. The air pressure elevated at the entrance area and then decreased as it approached the pipe's exit owing to the fully developed fluid velocity and the outflow boundary condition.