Performance characteristics of hybrid cooling towers

Oosthuizen, Pieter Cornelis (1995-09)

Thesis (MEng)--Stellenbosch University, 1995.

Thesis

ENGLISH ABSTRACT: Different wet/dry and dry/wet cooling tower configurations are investigated and the advantages and disadvantages of separate and combined (hybrid) configurations are discussed. Some existing hybrid towers are also discussed. The different plume prediction models that are found in the literature are investigated and the psychrometries behind the formation of visible plumes are discussed. Psychrometric models are given for a few different plume abatement tower geometries. A theoretical model is developed with which the thermal performance of hybrid towers can be predicted. This theoretical model makes use of adapted wet and dry cooling tower theories. A computer program was developed to determine the thermal performance of a parallel path air flow and series path water flow rectangular hybrid tower. A sample calculation of the hybrid tower solution, in which the converged values are used, is given. A wet cooling tower fill for use in the hybrid tower was tested, from which correlations for the transfer characteristics and the pressure drop coefficients were generated. Sample calculations to show how the transfer characteristics and the pressure loss coefficients were obtained from the experimental data are given. The Chebyshev method of numerical integration, that was used to determine the transfer characteristics, is discussed. A method for determining a more appropriate and accurate pressure loss coefficient is derived. Experiments were done on cylindrical and rectangular model cooling tower sectors to determine the size of the inlet circulation areas. Correlations with which the size of the ineffective fill area in wet cooling towers can be predicted were obtained from the experimental data.

AFRIKAANSE OPSOMMING: Verskeie nat/droeë en droeë/nat koeltoring konfigurasies is bespreek en die voor en nadele van afsonderlike en gekombineerde (hibriede) torings is beskou. 'n Studie is gemaak van bestaande hibriede torings. Modelle om die vorming van sigbare pluime te voorspel is ondersoek, en die psigrometrie agter die vorming van sigbare pluime word bespreek vir 'n paar hibriede koeltoring geometriee. 'n Teoretiese model is ontwikkel om die termiese vermoeë van 'n hibriede koeltoring te voorspel, asook die vermoeë van die toring om pluimvorming te voorkom. In die ontwikkeling van hierdie model is van bestaande nat en droeë koeltoring teorieë gebruik gemaak. 'n Rekenaar program is ontwikkel om 'n parallele lugvloei, serie watervloei reghoekige hibriede toring se verkoelingsvermoeë te bepaal, en 'n monsterberekening van die program se finale iterasie tydens so 'n oplosproses is gegee. 'n Nat koeltoring pakking vir gebruik in die hibriede toring is getoets, en korrelasies vir die bepaling van die pakking se oordrags (warmte en massa) karakteristiek en drukverlies koeffisient tydens verskillende bedryfstoestande is opgestel. 'n Monsterberekening is gedoen om te wys hoe die pakkingsdata verwerk is om die verskillende oordrags karakteristieke en drukverlies koeffisiente te bepaal. Die Chebyshev numeriese integrasie metode om die oordrag (warmte en massa) deur so 'n pakking te bepaal is ondersoek. 'n Metode om 'n drukverlieskoeffisient te bepaal waarmee die drukverlies deur die pakking meer akkuraat voorspel kan word is ontwikkel. Toetse is gedoen om die grootte van die lug sirkulasiearea deur die bundels van ronde en reghoekige model koeltoringseksies te bepaal. Vanaf hierdie resultate is korrelasies opgestel wat gebruik kan word om die grootte van die oneffektiewe pakkingsareas in koeltorings te voorspel.

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