Investigation of entropy generation, efficiency, static and ideal pressure recovery coefficient in curved annular diffusers

Abstract

The annular diffuser is used mostly in turbomachines for recovery of the discharge kinetic energy and increasing the total pressure. The performance of diffuser is strongly dependent on the geometry and inlet conditions. Therefore, the optimum design of the diffuser shape is highly important. On the other hand, it seems necessary to work on entropy generation in different geometries of diffusers to reach the maximum efficiency. In the present study, the turbulent flow in curved annular diffuser is numerically investigated for different area ratios (AR = 1.74, 2 and 2.3) and different turning angles (θ = 60°, 80° and 90°). Reynolds number based on mass averaged flow at the inlet is 136,822. In addition, the entropy generation rate due to turbulent and viscous dissipation, total entropy, volumetric entropy generation, static pressure recovery coefficient, ideal pressure recovery coefficient and diffuser effectiveness are studied. The results show that in order to design the curved annular diffusers to reach the maximum efficiency and minimum entropy generation in air-conditioning systems, the lowest value of area ratio and highest value of turning angle should be considered, respectively. Moreover, it was obtained that at constant area ratio, the entropy due to viscous dissipation and total entropy decrease with increasing the turning angle, while the diffuser effectiveness and static pressure recovery coefficient increase with increasing the turning angle. Also, by increasing the area ratio at constant turning angle, the volumetric entropy generation, total entropy and entropy due to turbulent dissipation increase.