Experimental investigation of an annular diffuser for axial fans at different inflow profiles

• Main Authors: Walter Johannes, Wurz Dieter, Hartig Stefan, Gabi Martin
• Format: Article
• Language: English
• Published: VINCA Institute of Nuclear Sciences 2017-01-01
• Series: Thermal Science
• Subjects: annular diffuser; flow separation; fan outflow profile; Preston method; pressure recovery
• Online Access: http://www.doiserbia.nb.rs/img/doi/0354-9836/2017/0354-98361600183W.pdf

Axial fans are used in power plants for fresh air supply and flue gas transport. A typical configuration consists of an axial fan and annular diffuser which connects the fan to the following piping. In order to achieve a high efficiency of the con-figuration, not only the components have to be optimized but also their interaction. The present study focuses on the diffuser of the configuration. Experiments are performed on a diffuser-piping configuration to investigate the influence of the velocity profile at the fan outlet on the pressure recovery of the configuration. Two different diffuser inlet profiles are generated, an undisturbed profile and a profile with the typical outlet characteristics of a fan. The latter is generated by the superposition of screens in the inlet zone. The tests are conducted at a high Reynolds number (Re ≈ 4∙105). Mean velocity profiles and wall shear stresses are measured with hydraulic methods (Prandtl and Preston tubes). The results show that there is a lack of momentum at the outer wall of the diffuser and high shear stresses at the inner wall in case of the undisturbed inflow profile. For the typical fan outlet profile it is vice versa. There are high wall shear stresses at the outer wall while the boundary layer of the inner wall lacks momentum. The pressure recovery of the undisturbed inflow configuration is in good agreement with other studies.