Evaluation of natural draught wet-cooling tower performance uncertainties

[摘要] ENGLISH ABSTRACT:A natural draught wet-cooling tower (NDWCT) was modelled using the Merkel method with animproved energy equation as recommended by Kloppers and Kroger (2005a) - referred to as theImproved Merkel method. The improved energy equation is used for calculating the heat rejection rate ofthe tower and includes the energy associated with water evaporation. The sensitivity indexes of aNDWCT were calculated numerically with the Improved Merkel method model. It was found that theperfonnance of a NDWCT is most sensitive to the fill Merkel number. The Natklos fill test facility atStellenbosch University was used to estimate typical uncertainties found in fill performancecharacteristics. The zeroth order uncertainty for the Merkel number and loss coefficient was calculated tobe 0.2100 m-1 and 0.4248 m- 1, respectively, while the first order uncertainty for the Merkel number andloss coefficient was calculated to be 0.1933 m- 1 and 0.2008 m-1, respectively. ASME requires that theuncertainty in tower capability has to be less than 6 % for a NDWCT perfonnance test to be deemedASME approved. Propagating typical measurement uncertainties found in NDWCT test standards andexperimental data into the tower capability showed that the 6 % uncertainty limit imposed by ASME isunrealistic and too stringent. Performance curve generator (PCG) is a software package developed thatgenerates NDWCT perfonnance curves. With these performance curves it is possible to easily andeffectively adjust the off-design test results in order to detennine whether the NDWCT has met itsguarantee or not.

[发布机构] Stellenbosch University