Simulating the Effect of Wind on the Performance of Axial Flow Fans in Air-Cooled Steam Condenser Systems

Abstract

The use of air-cooled steam condensers (ACSCs) is preferred in the chemical and power industry due to their ability to adhere to stringent environmental and water use regulations. ACSC performance is, however, highly dependent on the prevailing wind conditions. Research has shown that the presence of wind reduces the performance of ACSCs. It has been found that cross-winds (wind perpendicular to the longest side of the ACSC) cause distorted inlet flow conditions, particularly at the upstream peripheral fans near the symmetry plane of the ACSC. These fans are subjected to what is referred to as “two-dimensional” wind conditions, which are characterized by flow separation on the upstream edge of the fan inlets. Experimental investigations into inlet flow distortion have simulated these conditions by varying the fan platform height. Low platform heights resulted in higher levels of inlet flow distortion, as also found to exist with high cross-wind velocities. The similarity between platform height and cross-wind velocity is investigated in this study by conducting experimental and numerical investigations into the effect of distorted inlet flow conditions on the performance of various fan configurations (representative of configurations used in the South-African power industry). A correlation between system volumetric effectiveness, platform height, and cross-wind velocity is derived which provides a means to compare platform height and cross-wind velocity effects.

Axial Fan Performance under the Influence of a Uniform Ambient Flow Field

“…The drop of total efficiencỹt of about 43% at Φ = 0.15, = 90 ∘ , and = 0.258 from Figure 11 can best be roughly compared to the approx. 20% volumetric effectiveness decline found in [22] lower operating point Φ ≈ 0.1. Even though comparable figures may be concluded for more similar Φ, differences and variation in experimental and computational setup (fan design, ACC application and system characteristics, platform influence, operating point, etc.)…”

“…This may serve as a reference figure to the results from the presented work's examination in perpendicular configuration. For individual fans at the ACC perimeter, decreases of 60% to 80% are reported in [22], but they are subject to strong additionally induced drafts from the center fans. Unfortunately, the results and empirical model by Fourie et al do not translate well to the configuration of this work's approach, where no platform height exists.…”

“…It has been shown that flow detachment at the periphery of the ACC banks is caused by cross-flow under the platform, which is induced by the center fans' intake and natural ambient winds [8][9][10][11][12][13][14][15][16]. This reduces volumetric effectiveness of the cooling fans of down to 70% at the ACC perimeter [6,15,[17][18][19][20][21][22].…”

“…Although most of the cited works investigate the influence of induced cross-draft on perimeter fans at different platform heights, a comparison can be made of their findings to the uniform ambient flow field of the present work. Based on the Salta model [8], Fourie et al [22] suggest an empirical curve for the influence of ACC platform height and additional ambient cross-flow on the fan flow rate. The study shows substantial differences in cross-flow influence on fan performance due to fan design, and it points out the importance of fan position in the ACC array, that is, perimeter fan compared to center fans.…”

Axial Fan Blade Vibration Assessment under Inlet Cross-Flow Conditions Using Laser Scanning Vibrometry

“…Traditional "A-frame" designs consist of large diameter, low-pressure axial fans mounted horizontally below bundles of heat-exchanger tubes where the condensate is cooled by the fans' draft [2]. At the fans' inlets, the influence of cross-flow induced by neighboring fans and natural ambient winds, which typically reach magnitudes of 5 to 13 m/s or greater [3,4], is a major issue; it reduces the volumetric effectiveness of the cooling fans discernibly [5][6][7][8][9][10].…”