Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Melanie M. Derby / Power plants are significant water users, accounting for 15% of water withdrawals worldwide. To reduce water usage, compact condensers are required to enable air-cooled condensers and reduce infrastructure costs. Steam flow condensation was studied in 0.952-mm and 1.82-mm hydraulic diameter mini-gaps in an open loop experimental apparatus. The apparatus was validated with single-phase flow. Flow condensation experiments were conducted for a wide range of steam mass fluxes (i.e., 35–100 kg/m²s) and qualities (i.e., 0.2–0.9) in hydrophilic copper and hydrophobic Teflon-coated channels. Water contact angles were 70° and 110° on copper and Teflon, respectively, and in general, filmwise condensation was the primary condensation mode in the hydrophilic channel and dropwise condensation was the primary mode observed in the hydrophobic channel. Pressure drops were reduced by 50–80% in the hydrophobic channels. Condensation heat transfer was enhanced by 200–350% in hydrophobic mini-gaps over hydrophilic mini-gap due to dropwise condensation. Droplet dynamics (e.g., nucleation, coalescence and departure) were quantified during dropwise condensation. A model was created which includes droplet adhesion and drag forces for droplet departure diameters which were then correlated to heat transfer coefficients. An overall mean absolute error of 9.6% was achieved without curve fitting. Noncondensable gases can reduce heat transfer in industrial systems, such as power plants due to the additional layer of thermal resistance from the gas. Condensing steam-nitrogen experiments were conducted for nitrogen mass fractions of 0–30%; the addition of nitrogen reduced heat transfer coefficients by up to 59% and 30% in hydrophilic and hydrophobic mini-gaps, respectively. It was found that during dropwise condensation, the noncondensable layer was perturbed by cyclical droplet motion, and therefore heat transfer coefficients were increased by 2–5 times compared with filmwise condensation of the same mass fraction of nitrogen.

Die in diesem Bericht vorgestellten Experimente betreffen die Kondensation von Dampf in horizontalen bzw. leicht geneigten Rohren bei hohen auftretenden Temperaturdifferenzen bis zu über 200 K. Weitere Besonderheiten sind die detaillierte Untersuchung des transienten Verhaltens eines nichtkondensierbaren Gases mit einer neuartigen Messtechnik sowie die Ermittlung des Einflusses des Gases auf den Kondensationsvorgang. Beim Experiment wurden schnelle Übergangsvorgänge ausgelöst, indem ein in einer Kühlwanne liegendes, leicht geneigtes Wärmeübertragerrohr plötzlich mit dem Dampfraum eines unter Druck stehenden Kessels verbunden wurde. Dabei wurden im Rohr unterschiedliche Anfangsbedingungen hinsichtlich der Vorlage von nichtkondensierbaren Gasen (in diesem Falle Luft) eingestellt. Es wurden Versuche mit Atmosphärendruck, mit erhöhtem Druck, aber auch mit vorheriger Evakuierung des Versuchsrohrs durchgeführt. Durch eine Instrumentierung mit neuartigen Nadelsonden, die eine Phasendetektion kombiniert mit einer schnellen lokalen Temperaturmessung ermöglichen, konnte die Umverteilung von Dampf, Kondensat und nichtkondensierbarem Gas als Funktion der Zeit beobachtet werden. Damit bieten die erhaltenen Daten die Möglichkeit, insbesondere die in den Thermohydraulikprogrammen vorhandenen Optionen zur Berechnung der Ausbreitung von nichtkondensierbaren Gasen unter transienten Bedingungen zu validieren.

Master of Science / Department of Mechanical and Nuclear Engineering / Hitesh Bindra / Storing excess thermal energy in a storage media that can later be extracted during peak-load times is one of the better economical options for nuclear power in future. Thermal energy storage integration with light water-cooled and advanced nuclear power plants is analyzed to assess technical feasibility of different storage media options. Various choices are considered in this study; molten salts, synthetic heat transfer fluids, and packed beds of solid rocks or ceramics. In-depth quantitative assessment of these integration possibilities are then analyzed using exergy analysis and energy density models. The exergy efficiency of thermal energy storage systems is quantified based on second law thermodynamics. The packed bed of solid rocks is identified as one of the only options which can be integrated with upcoming small modular reactors. Directly storing thermal energy from saturated steam into packed bed of rocks is a very complex physical process due to phase transformation, two phase flow in irregular geometries and percolating irregular condensate flow. In order to examine the integrated physical aspects of this process, the energy transport during direct steam injection and condensation in the dry cold randomly packed bed of spherical alumina particles was experimentally and theoretically studied. This experimental setup ensures controlled condensation process without introducing significant changes in the thermal state or material characteristics of heat sink. Steam fronts at different flow rates were introduced in a cylindrical packed bed and thermal response of the media was observed. The governing heat transfer modes in the media are completely dependent upon the rate of steam injection into the system. A distinct differentiation between the effects of heat conduction and advection in the bed were observed with slower steam injection rates. A phenomenological semi-analytical model is developed for predicting quantitative thermal behavior of the packed bed and understanding physics. The semi-analytical model results are compared with the experimental data for the validation purposes. The steam condensation process in packed beds is very stable under all circumstances and there is no effect of flow fluctuations on thermal stratification in packed beds. With these experimental and analytical studies, it can be concluded that packed beds have potential for thermal storage applications with steam as heat transfer fluid. The stable stratification and condensation process in packed beds led to design of a novel passive safety heat removal system for advanced boiling water reactors.

Die in diesem Bericht vorgestellten Experimente betreffen die Kondensation von Dampf in horizontalen bzw. leicht geneigten Rohren bei hohen auftretenden Temperaturdifferenzen bis zu über 200 K. Weitere Besonderheiten sind die detaillierte Untersuchung des transienten Verhaltens eines nichtkondensierbaren Gases mit einer neuartigen Messtechnik sowie die Ermittlung des Einflusses des Gases auf den Kondensationsvorgang. Beim Experiment wurden schnelle Übergangsvorgänge ausgelöst, indem ein in einer Kühlwanne liegendes, leicht geneigtes Wärmeübertragerrohr plötzlich mit dem Dampfraum eines unter Druck stehenden Kessels verbunden wurde. Dabei wurden im Rohr unterschiedliche Anfangsbedingungen hinsichtlich der Vorlage von nichtkondensierbaren Gasen (in diesem Falle Luft) eingestellt. Es wurden Versuche mit Atmosphärendruck, mit erhöhtem Druck, aber auch mit vorheriger Evakuierung des Versuchsrohrs durchgeführt. Durch eine Instrumentierung mit neuartigen Nadelsonden, die eine Phasendetektion kombiniert mit einer schnellen lokalen Temperaturmessung ermöglichen, konnte die Umverteilung von Dampf, Kondensat und nichtkondensierbarem Gas als Funktion der Zeit beobachtet werden. Damit bieten die erhaltenen Daten die Möglichkeit, insbesondere die in den Thermohydraulikprogrammen vorhandenen Optionen zur Berechnung der Ausbreitung von nichtkondensierbaren Gasen unter transienten Bedingungen zu validieren.

This diploma thesis deals with design of surface condensers with axial steam inlet which are widely used in the energy industry. In the practical part, hydraulic and heat calculation, dump-tube design and calculation of by-pass were made to design surface condenser with axial steam inlet. Two types of surface condenser were designed in order to compare impact of two different heat transfer tube materials. Stainless steel and copper-nickel alloy were used for condenser calculation. Stainless steel and copper-nickel alloy condensers were compared in order to weight calculation and condenser price estimation.

The diploma thesis named Heat exchanger with a combined condensation deals with design of the heat exchanger with a combined condensation. The first part is a brief research about direct-contact heat exchangers. The next part describes physical principles of direct-contact heat transfer mechanisms and a method of calculation is proposed. After that the bundle with basic dimension of heat exchanger is designed. The mixing chamber is designed based on these dimension. Technical documentation of a heat exchanger with combined condensation is an integral part of the thesis.

The Master´s thesis is dealing with water-cooled condensers and is splitted into three main parts. The first section provides general knowledge about condensers and heat exchangers, including the basic information of hydrophobic surfaces. These surfaces were used during verifying the impact of hydrophobicity on the heat exchange in water steam. The second section describes an experimental testing. It shows the difference between hydrophobic and nonhydrophobic surfaces and their impact on the heat exchange. The third and the last part of this thesis is design and calculation of water-cooled condenser. The design of the condenser is supported by drawings placed in attachement.