The effectiveness of axial flow fans in a-frame plenums

[摘要] ENGLISH ABSTRACT: The ultimate goal of this project is to ensure a better understanding of the governingmechanisms present when flow distorting components are installed in close proximity ofan axial flow fan.The effect of different parameters on the operation of axial flow fans is investigated. Theseparameters are divided into flow enhancing and flow reduction effects. The performanceof an axial flow fan can be enhanced by changing the tip clearance, by adding a soliddisc to the hub of the fan or by varying the number of fan blades. Flow reductions arecaused by components such as inlet grids, walkways and their supporting structures, heatexchangers and windwalls.The effects of flow enhancing components are measured and compared to the results ofother authors. The sensitivity of these effects to parameters such as the type of fan rotorand the specific system in which the rotor is installed is highlighted.The system effect (the interaction between the fan rotor and flow resistances in closeproximity of each other) of individual components, as well as the combination of differentcomponents, is predicted both theoretically and experimentally. These predictions arecompared to measured data relevant to the components in an installation where the systemeffects are present. The results are correlated to the kinetic energy flux coefficient of theflow at different locations within the installation.Experimental data obtained from a full scale unit (inlet shroud diameter of 9,216 m) areused to compare to scaled data from the model (inlet shroud diameter of 1,542 m). Thehub to tip ratio of the axial flow fans investigated is 0,15.The most important conclusions are that the performance of the type of axial flow fanunder investigation can be improved by reducing its tip clearance and by installing a soliddisc to the downstream side of the rotor. An increase in the number of blades of the fanleads to only marginal improvements in the fan performance. The overall performance ofthe system can also be improved by removing some of the flow resisting components, orby changing their relative positions. All these conclusions are based on the assumptionthat the power input to the fan rotor remains constant.

[发布机构] Stellenbosch University