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Performance evaluation of a hybrid (dry/wet) cooling system

dc.contributor.advisorReuter, Hanno Carl Rudolfen_ZA
dc.contributor.advisorOwen, Michaelen_ZA
dc.contributor.authorGraaff, Andre Hendrien_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.en_ZA
dc.date.accessioned2017-02-21T10:31:12Z
dc.date.accessioned2017-03-29T12:13:42Z
dc.date.available2017-02-21T10:31:12Z
dc.date.available2017-03-29T12:13:42Z
dc.date.issued2017-03
dc.identifier.urihttp://hdl.handle.net/10019.1/101146
dc.descriptionThesis (MEng)--Stellenbosch University, 2017.en_ZA
dc.description.abstractENGLISH ABSTRACT: The performance of a hybrid (dry/wet) cooling system (HDWCS) is investigated. The HDWCS aims to compete with dry cooling systems with added performance stability during hot ambient periods. The system consists of two stages – the first, finned tube bundles operating dry, and the second, a bare tube bundle operating dry or wet. A numerical performance prediction model is developed to predict the performance of the HDWCS in terms of outlet process medium temperature, outlet air temperature and air-side pressure loss. For the finned tube bundles, the heat transfer coefficient correlation and pressure loss correlation proposed by Ganguli et al. (1985) are used to predict the air-side heat transfer coefficient and air-side pressure drop over the bundle. For the bare tube bundle under dry operation, the air-side heat transfer coefficient of Khan et al. (2006) and the air-side pressure drop correlation of Reuter and Anderson (2016) is used. For the bare tube bundle under wet operation, the mass and heat transfer coefficients proposed by Mizushina et al. (1967) are used together with the air-side pressure drop correlation from Reuter and Anderson (2016) to predict the thermal performance. Analysis of both the finned tube bundles and the bare tube bundle are based on a so-called integral method, where the outlet conditions were determined across the bundles from inlet conditions. Experimental work investigates air flow rate, to avoid high air pressure drop across the bare tube bundle, and the minimum water flow rate to avoid dry-out inside the bare tube bundle are determined. A maximum air mass velocity of Gav = 3 kg/sm2 and a minimum water mass velocity of Гdw/do = 1.89 kg/sm2 is suggested. Thermocouple attachment methods are investigated for the bare tube bundle under wet operation. It is found that by attaching the thermocouples with 4 zip ties instead of 3, the certainty for measuring water temperature is significantly improved under the suggested air and water flow rates. The air-side pressure drop across the bare tube bundle is influenced by the number of tube rows present, together with air and water flow rates. The pressure drop under wet operation is slightly higher than under dry operation. The bare tube bundle’s dimensions are determined from a parametric study, delivering a bare bundle, 800 mm in both width and height which can boost the cooling systems’ performance by between 35 % and 140 % relative to a conventional system, depending on air relative humidity at an ambient dry bulb temperature of 32 ºC. Inlet process medium temperature remains at 38 ºC. The HDWCS can serve as a strong competitor, delivering a significant increase in performance compared to dry coolers especially during hot periods, when the performance of dry only cooling systems are low.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die prestasievermoë van ʼn hibriede (droog/nat) verkoelingstelsel (HDNVS) word ondersoek. Dit word gedoen om sodoende ʼn verkoelingstelsel te ontwikkel, wat met droëverkoelingstelsels kan meeding en `n beter prestasievermoë gedurende hoë omgewingslugtemperature kan handhaaf. Die beoogde HDNVS bestaan uit 2 dele. Die eerste deel bevat vinbuisbundels wat net droog bedryf word terwyl die tweede deel uit `n skoonbuisbundel bestaan wat droog of nat bedryf kan word. `n Numeriese voorspellingsprogram is ontwikkel om die prestasie, in terme van die uitlaat-temperature van lug- en prosesmedium te bepaal, gegee die inlaat-toestand van prosesmedium en atmosferiese lug. Korrelasies vanuit die literatuur word soos volg geïmplementeer: vir die vinbuisbundels is die warmteoordragskoëffisiënt en lugkantdrukverlies-korrelasies van Ganguli et al. (1985) gebruik. Wanneer die skoonbuisbundel nat bedryf word, is die massa- en warmteoordragskoëffisiënt van Mizushina et al. (1967) geïmplementeer en wanneer dit droog bedryf word, die warmteoordragskoëffisiënt van Khan et al. (2006). Reuter en Anderson (2016) verskaf die lugkantdrukverlies-korrelasies vir die skoonbuisbundel wanner dit nat of droog bedryf word. Die vinbuis- én skoonbuisbundel is volgens `n sogenaamde integralemetode opgelos, met ander woorde, net die uitlaat-toestande word bereken vanaf die gegewe inlaat-toestande. Eksperimentele werk sluit in (1) die ondersoek na watervloeipatrone aan die lugkant van die skoonbuisbundel onder kritieke lugvloeitoestande asook uitdroogkolle binne in die skoonbuisbundel, (2) twee hegtingsmetodes vir termokoppels aan skoonbuise, om die meetsekerheid van watertemperatuur te verseker en (3) die effek van aantal buisrye, teenwoordig in die skoonbuisbundel, op die lugdrukval oor die bundel onder verskeie nat- en droëvloeitempo’s. Daar is gevind dat kritieke lugvloeitempo’s tot hoë drukverliese oor die skoonbuisbundel lei en `n maksimum lugmassasnelheid van Gav = 3 kg/sm2 word voorgestel, terwyl `n minimum watermassasnelheid van Гdw/do = 1.89 kg/sm2 voorgestel word om uitdroogkolle in die bundel te vermy. Vir die termokoppels is daar gevind dat indien vier kabel bande gebruik word om die termokoppel aan die skoonbuis te heg, verseker dit die meetpunte bly nat ongeag die lug- en watervloeitempo’s. Laastens is daar gevind dat die lugdrukval oor die skoonbuisbundel, `n sterk funksie van die aantal buisrye is, gevolg deur die lug- en watermassasnelhede. Wanneer die skoonbuisbundel nat bedryf word, is die drukval ietwat hoër as vir droë bedryf. Vanaf die parameterstudie is daar gevind dat `n vierkantige bundel met `n breedte en hoogte van 800 mm, die prestasievermoë met tussen 35 % en 140 % kan verbeter, in vergelyking met `n konvensionele droëverkoelingstelsel, afhangende van die relatiewe lughumiditeit. Die prestasie is bewerkstellig by `n lugtemperatuur van 32 ºC en prosesmediumtemperatuur van 38 ºC. Vanuit die studie is daar bevind dat die HDNVS as `n sterk mededinger kan dien vir droëverkoelingstelsels en die vermoë het om `n wesenlike impak te maak op verkoelingsprestasie gedurende tydperke van hoë lugtemperature – wanneer die verkoelingsvermoë van droëverkoelers drasties afneem.af_ZA
dc.format.extent136 pages : illustrationsen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.subjectHybrid systems -- Coolingen_ZA
dc.subjectMultistage coolingen_ZA
dc.subjectHeat transferen_ZA
dc.subjectCooling systemsen_ZA
dc.subjectUCTDen_ZA
dc.titlePerformance evaluation of a hybrid (dry/wet) cooling systemen_ZA
dc.typeThesisen_ZA
dc.rights.holderStellenbosch Universityen_ZA


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