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Condensation is an important phenomenon in many engineering applications. Phase change processes are efficient ways of heat removal, as the latent heat of condensation and boiling provides high heat transfer coefficients. The calculation of the heat transfer in phase change processes is crucial for designing heat exchangers. The currently constructed and designed nuclear power plants satisfy higher safety standards due to the intense use of passive safety systems. Passive safety systems operate without external power supply or operator intervention, only relying on physical phenomena, such as natural circulation and gravity driven flows. New heat exchanger designs are applied for emergency core cooling and heat removal from the containment. While classical heat exchangers are optimized for high plant efficiency, the passive components like emergency condensers and containment cooling condensers have to be optimized for a wider range of operation parameters during the progression of an accident. In the nuclear industry one-dimensional system codes are prevailing to simulate entire nuclear power plants and to analyze the reliability of the safety systems. However, threedimensional techniques, such as computational fluid dynamics, gain more attention particularly for studies of complex multiphase phenomena. The two approaches are not interchangeable, the use and the development of both simultaneously helps to improve the simulation possibilities for power plants and big components. Widely used representatives of one-dimensional simulation tools are the codes RELAP5 and TRACE, developed by the U.S.NRC. These codes are able to capture most of the phenomena occurring in the power plant however, it is part of the safety philosophy to permanently question and improve the performance of these tools. The computational fluid dynamics codes provide an efficient and powerful way to simulate single components in the power plant. These codes solve the continuity equations of the fluid in a three-dimensional domain using finite volume methods. The consideration of the three dimensions helps to better understand the flow behavior and heat transfer processes. However, modeling of two phase flows, in particular with phase change, is leading to computationally intense calculations. Therefore, the simulation of phase change heat transfer remains a challenge in computational fluid dynamics. In this thesis condensation models are introduced and evaluated and the application of these models to the emergency cooling system is discussed. The emergency condenser of the KERENA reactor, serving as a passive device for depressurization and decay heat removal, is equipped with a bundle of horizontally oriented or slightly inclined tubes, which are immersed in a cold water tank. The pipes are connected to the reactor pressure vessel