Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In this study, one and two-dimensional models are developed for the evaluation of the thermal performance of a delugeable flat tube bundle to be incorporated in the second stage of an induced draft hybrid (dry/wet) dephlegmator (HDWD) of a direct air-cooled steam condenser (ACSC). Both models are presented by a set of differential equations. The one-dimensional model is analysed analytically by using three methods of analysis which are: Poppe, Merkel, and heat and mass transfer analogy. The two-dimensional model is analysed numerically by means of heat and mass transfer analogy method of analysis whereby, the governing differential equations are discretised into algebraic equations using linear upwind differencing scheme. The two-dimensional model’s accuracy is verified through a comparison of the two dimensional solutions to one dimensional solutions. Satisfactory correlation between the one and two-dimensional results is reached. However, there is a slight discrepancy in the solutions, which is mainly due to the assumptions made in one-dimensional model. The effect of tube height, tube pitch, tube width, deluge water mass flow rate, frontal air velocity, steam, and air operating conditions on the heat transfer rate and air-side pressure drop for both wet and dry operating modes are investigated. The long tube height, large tube width, small tube pitch, and high frontal air velocity are found to increase the tube bundle’s performance. However, this performance is associated with a high airside pressure drop. The performance of the deluged flat tube bundle is found to be less sensitive to the changes in the deluge water mass flow rate and air operating conditions. Furthermore, the best configuration of a delugeable flat tube bundle is identified through a comparison to round tube bundle presented by Anderson (2014). The performance of the round tube bundle is found to be around 2 times, and 1.5 times of that of flat tube bundle, when both bundles operate as an evaporative and dry air-cooled condenser respectively. / AFRIKAANSE OPSOMMING: In hierdie studie is een en twee-dimensionele modelle ontwikkel vir die evaluering van die termiese prestasie van 'n benatbare plat buis bundel in die tweede stadium van 'n geïnduseerde ontwerp hibriede (droë / nat ) deflegmator van 'n direkte lugverkoelde stoom kondensator. Beide modelle is aangebied deur 'n stel van differensiaalvergelykings. Die een-dimensionele model is analities ontleed deur die gebruik van drie metodes van analise wat: Poppe, Merkel, en die hitte en massa-oordrag analogie. Die twee-dimensionele model is numeries ontleed deur middel van hitte en massa-oordrag analogie metode van analise waardeur , die regerende differensiaalvergelykings gediskretiseer in algebraïese vergelykings met behulp van lineêre windop differensievorming skema. Die tweedimensionele model se akkuraatheid is geverifieer deur 'n vergelyking van die twee dimensionele oplossings te een dimensionele oplossings. Bevredigende korrelasie tussen die een en twee-dimensionele resultate bereik word. Maar daar is 'n effense verskil in die oplossings, wat is hoofsaaklik te wyte aan die aannames wat gemaak in een-dimensional model. Die effek van buis hoogte, buis toonhoogte, buis breedte, vloed water massa-vloeitempo, frontale lug snelheid, stoom, en in die lug werktoestande op die hitte oordrag snelheid en lug - kant drukval vir beide nat en droë maatskappy modi word ondersoek. Die lang buis hoogte, groot buis breedte, klein buisie toonhoogte, en 'n hoë frontale lug snelheid gevind die buis bundel se prestasie te verhoog. Tog is hierdie prestasie wat verband hou met 'n hoë lug - kant drukval. Die prestasie van die oorstroom plat buis bundel gevind word minder sensitief vir die veranderinge in die vloed water massa-vloeitempo en lug werktoestande. Verder is die beste opset van 'n benatbare plat buis bundel geïdentifiseer deur 'n vergelyking met ronde buis bundel aangebied deur Anderson (2014). Die prestasie van die ronde buis bundel gevind word om 2 keer, en 1.5 keer van daardie plat buis bundel , wanneer beide bundels funksioneer as 'n damp en droë lugverkoelde kondensor onderskeidelik.