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Application of the CUPID Code for Simulation of Subcooled Flow Boiling Phenomena
Yazan Alatrash1,2, Han Young Yoon1,2, Yun Je Cho2
1University of Science and Technology; 2Korea Atomic Energy Research Institute
In this study, the subcooled flow boiling experiment (DEBORA) is simulated using a two phase three-dimensional thermal hydraulics code called CUPID. Subcooled boiling at heated wall is modeled by the RPI wall boiling partitioning model. In this model, heat transfer from the heated wall surface to the fluid is expressed as a sum of surface quenching heat transfer, evaporation heat flux, and single-phase convection heat flux. As the working fluid in the experiment is Freon (R12), the fluid properties for R12 are implemented inside the CUPID code.
Comparison between the calculated and experimental data of the radial gas void fraction showed that the CUPID code predicted the subcooled flow boiling correctly. Sensitivity studies are performed to analyze the important parameters influencing the subcooled flow boiling. Different models for the bubble departure diameter, nucleation site density and bubble departure frequency are implemented and compared against each other. Effect of the non-drag forces such as the lift force and wall lubrication forces were also examined.
Temperature Field Measurements in Sub-cooled Boiling Using the Laser Induced Fluoresce Technique (LIF)
Bandar Alkhudhiri, Sero Yang, Yassin A. Hassan
Texas A&M University
Temperature measurements are performed in sub-cooled boiling experiments through a single-heated side rectangular test channel at various conditions. The temperature measurements involve the use of the Laser Induced Fluorescence (LIF) method with one heated single-phase (3.9 kw/m2) and two boiling conditions (30.9 and 36.6 kw/m2). Two flow rates are considered, for each heating level, and given by the Reynold’s number (Re) of 8121 and 20523. For the boiling cases, bubbles are allowed to slide along the heated surface and temperature fields are obtained along the bubbles sliding distance in the axial direction. Radial temperature profiles are mapped out to display the temperature distributions at various axial locations. The resultant temperature fields reveal insightful information about the temperature distribution in each condition. Boiling bubbles induce major changes to the temperature fields. In regions far from the heated wall, the temperature profiles are seen to fall within the range of the bulk fluid temperature values (21.6 ºC ± 1 ºC), as registered by the means of thermocouples. A large increase in temperature is observed near the heated wall (and at the sliding distance) to approximately 29.6 ºC ± 2 ºC. The reference temperature values obtained for this region by the infrared camera are seen to fluctuate between 30.9 and 31.9 ºC. A higher discrepancy is observed near the heated wall area due to weaker fluorescent signals can be captured in this region. The thermal boundary layers are shown to grow thicker with higher heating input and higher flow rates. The LIF temperature measurements in this study presents experimental investigation of the influence of nucleate boiling on temperature fields near wall/liquid interface. The whole-field method of LIF is shown to be useful to measure the developing thermal boundary layer, due to nucleate boiling, in contactless fashion using a fluorescent dye with a high speed camera.
Water Vapor Condensation in Containments: Numerical Model and Validation
Ulrich Bieder, Axelle Herbette
In the event of a loss of coolant accident (LOCA) in a pressurized nuclear reactor, large quantities of water vapor and hydrogen might be released into the containment building. Increasing pressure and the risk of hydrogen deflagration can threaten the containment integrity. Water vapor condensation on cold containment structures modify the possible load on the containment structures. On one hand, the total pressure reduces due to the decrease of the water vapor content of the containment atmosphere. On the other hand, the concentration of hydrogen increases, which can reach locally the threshold of deflagration or detonation. In order to predict transients of the pressure and the concentrations of gaseous species in reactor containments after a LOCA, a condensation model was implement in the TrioCFD code.
The physical model as well the implementation in the CEA OpenSource CFD code “TrioCFD” are described. Validation is presented in two steps. In a first step, verification tests are discussed to show that the condensation model is implemented correctly in the CFD code. In a second step, the model is validated against experimental data of the International Standard Problem ISP47. In this benchmark, a steady state situation was created experimentally in the MISTRA test containment of the CEA. In the presence of a non-condensable gas in the test vessel (air), an equilibrium was achieved between water vapor injection and water vapor condensation on temperature controlled cold walls (Phase I of the MISTRA experiment of ISP47). This steady state situation was analyzed with the new condensation model. It is shown that the model results are sensitive to both meshing and boundary conditions. For a good comparison to the experiment, it is necessary to take into account the spurious condensation on external vessel walls. The calculation represents well the experiment when all condensation paths are modelled correctly.
Numerical Prediction of Slug Flow Boiling Heat Transfer on a Downward-facing Heated Wall
Muritala Alade Amidu, Yacine Addad
Khalifa University of Science and Technology
This paper presents a mechanistic wall boiling model for flow boiling on a downward-facing heated wall which is characterized by the presence of vapor slugs on the heated wall at the pre-CHF condition. Essentially, this boiling model is an extension of the well-known RPI boiling model which was initially developed based on dispersed small spherical bubbles on the heated wall. The fundamental assumption of the RPI model sharply contrasts with the real situation during flow boiling on a downward-facing heated surface because of the presence of large scale interface bubbles (vapor slugs) that are virtually attached (separated from the wall by a thin liquid film) to the wall due to buoyancy effect. Therefore, the existing wall boiling model might not be adequate for a situation like this because the heat transfer governing mechanisms of vapor slug (deformable shape) is different from that of dispersed small spherical bubbles. In this article, a liquid film conduction model that captures the wall heat transfer governing mechanisms of vapor slug is coupled with the existing wall boiling model and the new extended wall boiling model is implemented within the solution framework of hybrid multiphase flow model in OpenFoam. The hybrid model combines Eulerian multi-fluid model (for the dispersed regime) and volume of fluid model (for the large scale interface vapor slug regime). With the hybrid multiphase flow model, different multiphase morphologies coexisting in the flow are duly accounted for. The extended wall boiling model shows an improved prediction of the experimental data of flow boiling heat transfer on a downward-facing heated wall when compared with the prediction by the existing wall boiling model.