Perimeter fan performance in forced draught air-cooled steam condensers

[摘要] ENGLISH ABSTRACT: Axial flow fan arrays form part of air-cooled steam condensers in direct drycooledpower plants. This dissertation investigates the performance of axial flowfans when located at the perimeter of a fan array. The perimeter (or edge) fansmay experience a reduction in air flow through the fan due to the prevalence ofdistorted inlet conditions upstream of the fan. The reduction in air flow leads to areduction in the heat transfer capability of the steam condenser and a consequentreduction in the electricity output of the power plant.Due to the physical size of an air-cooled condenser, full-scale experiments areoften impractical and computational fluid dynamics (CFD) is used to model itsperformance under various conditions. To limit the size of the CFD model theaxial flow fans in the CFD analysis are represented by means of simplifiedmethods. Three different simplified methods are presented and applied to a CFDmodel of a single axial flow fan, namely the pressure jump method (PJM),actuator disc method (ADM) and extended actuator disc method (EADM). Theresults are compared to experimental values. The comparison highlights thelimitations of the models: The ADM fails to model fan performance correctly atlow flow rates, while the PJM ignores the variation in fan blade properties atdifferent locations within the fan rotor. The EADM is presented as animprovement on both the other two models.A multiple fan test facility is constructed, consisting of three 630 mm diameterfans extracting air from a common inlet chamber. The inlet chamber isconstructed in such a way that one of the three fans act as the perimeter (edge)fan. The floor of the inlet chamber can be adjusted to increase or reduce the inletflow distortion experienced by the edge fan. Six different fan configurations aretested in the position of the edge fan and an empirical method is derived by whichthe volumetric effectiveness of an edge fan can be predicted. The experimentalresults are compared to CFD results for the same facility using the three differentsimplified simulation methods investigated previously. Particle image velocimetry(PIV) measurements are also performed upstream of the edge fan and the velocityprofiles at the inlet of the fan are compared to the profiles obtained numerically.The comparisons show that the EADM predicts the performance of the edge fanmore accurately than the ADM en PJM.The effect of adding a walkway and removing the bell mouth upstream of theedge fan was investigated using the EADM. The results are used to show thelocation of the loss mechanisms upstream of the edge fan. The addition of awalkway moves the location of the pressure loss away from the edge fan bellmouth towards the edge of the walkway. Consequently the distortion directlyupstream of the edge fan is reduced and its volumetric effectiveness increased.The effect of removing the edge fan's bell mouth is similar to the effect of addinga walkway upstream of the edge fan.

[发布机构] Stellenbosch University