Experimental investigation of the effect of perimeter windscreens on air-cooled condenser fan performance

Abstract

Perimeter windscreens are finding application in large air-cooled condensers (ACCs) as a mechanism to mitigate the negative effects of wind on ACC fan performance and dynamic blade loading. The limited literature specific to perimeter windscreens is inconsistent and the mechanisms by which these screens impact fan behaviour are not well understood. This study investigates the influence of perimeter windscreens on ACC fan volumetric effectiveness under windy conditions using a laboratory based experimental apparatus consisting of a scaled fan row consisting of three fans in the wind direction. Three different porous windscreen materials (differing solidity) were investigated along with the effect of varying windscreen height. A controllable cross-flow (wind) was achieved by connecting the apparatus to a low speed wind tunnel. Fan volumetric flow rate and shaft power were measured and flow visualization was achieved by means of particle imagery velocimetry to provide insight into the reasons for the observed fan behaviour. The apparatus corresponds to a full-scale ACC for which data relating to perimeter windscreen effects was available in the literature. A good correlation to these full-scale measurements was achieved giving confidence in the validity of the results of this study.Perimeter windscreens were observed to degrade edge fan volumetric effectiveness under windy conditions relative to the no-screen case in almost all cases considered in this study although evidence of a recovery of volumetric effectiveness was observed at high cross-flow (β = 0.36) for the case where a low solidity screen (α = 0.5) was installed across half or more of the platform inlet (L ≥ 0.5). An improvement in cooling effectiveness of up to 30% was observed relative to the no-screen case for the aforementioned screen configurations indicating that such perimeter windscreens may benefit the effective cost of cooling in ACCs under high wind conditions. The PIV flow visualization identifies deflection of the flow past the edge fan as the reason for the reduction in fan volumetric effectiveness when screens are installed. The negative impact of this deflection is counteracted by permeation of flow through the screen and into the edge fan when a low solidity screen covers a large portion of the platform inlet.It can therefore be concluded that, for the low platform ACC simulated in this study, perimeter windscreens are detrimental to ACC performance except at very high wind speeds. Use of low solidity retractable screens that can be deployed under high wind conditions (taking into account structural limitations) may have merit. This works extends the understanding of perimeter windscreen effects on ACC fans by investigating the effect of screen solidity and height in a controllable and validated experimental facility. It provides insight into the mechanisms through which perimeter screens influence ACC fans that can be used to further develop and improve the potential benefits of these screens.