Thermo-fluid dynamics of separated two-phase flow

Ph.D.Novak Zube

Bubble Lift-off Size in Forced Convective Subcooled Boiling Flow

Forced convective subcooled boiling flow experiments were conducted in a BWR-scaled vertical upward annular channel. Water was used as the testing fluid, and the tests were performed at atmospheric pressure. A high-speed digital video camera was applied to capture the dynamics of the bubble nucleation process. Bubble lift-off diameters were obtained from the images for a total of 91 test conditions. A force balance analysis of a growing bubble was performed to predict the bubble lift-off size. The dimensionless form of the bubble lift-off diameter was formulated to be a function of Jacob number and Prandtl number. The proposed model agreed well with the experimental data within the averaged relative deviation of ±35.2 %

Nucleate Pool Boiling Heat Transfer in Wickless Heat Pipes (Two-Phase Closed Thermosyphons): A Critical Review of Correlations

Innovation and Networks Executive Agency (INEA

Scaling criteria for modeling natural- and forced-convection loops. [PWR]

Nuclear reactor safety regulations have required extensive thermal-hydraulic testing of simulated reactor systems and components. In view of the inherent difficulties associated with full-scale testing, scale models for prototype systems have been extensively used to predict the behavior of nuclear reactor systems during normal and abnormal operations as well as under accident conditions. Several studies have been performed to establish similarity relations between a prototype and scale model. It is the purpose of the present study to develop scaling criteria for a forced and natural circulation loop under single- and/or two-phase flow conditions, and to apply the criteria to obtain the preliminary conceptual design parameters for the B and W 2 x 4 loop system. The 2 x 4 loop scaled system contains representative components of all thermal-hydraulic systems considered important in performing tests to obtain data representative of the response of the prototype plant

Interfacial Area Transport of Vertical Upward Bubbly Two-Phase Flow in an Annulus

In relation to the development of the interfacial area transport equation in a subcooled boiling flow, the one-dimensional interfacial area transport equation was evaluated by the data taken in the hydrodynamic separate effect tests without phase change for an adiabatic air-water bubbly flow in a vertical annulus. The annulus channel consisted of an inner rod with a diameter of 19.1 mm and an outer round tube with an inner diameter of 38.1 mm, and the hydraulic equivalent diameter was 19.1 mm. Twenty data sets consisting of five void fractions, about 0.050, 0.10, 0.15, 0.20, and 0.25, and four superficial liquid velocities, 0.272, 0.516, 1.03, and 2.08 m/s were used for the evaluation of the one-dimensional interfacial area transport equation. The one-dimensional interfacial area transport equation agreed with the data with an average relative deviation of ±8.96 %. Sensitivity analysis was also performed to investigate the effect of the initial bubble size on the interfacial area transport. It was shown that the dominant mechanism of the interfacial area transport was strongly dependent of the initial bubble size

General formulation of an HCDA bubble rising in a sodium pool and the effect of nonequilibrium on fuel transport

This report which improved the formulation of the previous reports is designed to investigate the effect of the interfacial nonequilibrium mass transfer and the radiative heat transfer on the amount of the fuel vapor condensed before the bubble reaches to the cover-gas region. Consideration is given to a fuel dominated bubble which is assumed to have just penetrated into the sodium pool in a spherical form subsequent to an Hypothetical Core Disruptive Accident (HCDA). The two-phase bubble mixture as it rises through the sodium pool to the cover-gas region is formulated. The formulation takes into account the effects of the nonequilibrium mass transfer at the interfaces and of the radiative cooling of the bubble as well as the kinematic, dynamic and thermal effects of the surrounding fields. The results of calculation for the amount of the fuel vapor condensed before the bubble reaches the cover-gas region are presented over a wide possible range of the evaporation coefficient as well as the liquid sodium-bubble interface absorbtivity

Local phase distribution and interfacial area in a horizontal bubbly two-phase flow

Short communication

Modeling of Bubble-Layer Thickness for Formulation of One-Dimensional Interfacial Area Transport Equation in Subcooled Boiling Two-Phase Flow

In relation to the formulation of one-dimensional interfacial area transport equation in a subcooled boiling flow, the bubble-layer thickness model was introduced to avoid many covariances in cross-sectional averaged interfacial area transport equation in the subcooled boiling flow. The one-dimensional interfacial area transport equation in the subcooled boiling flow was formulated by partitioning a flow region into two regions; boiling two-phase (bubble-layer) region and liquid single-phase region. The bubble-layer thickness model assuming the square void peak in the bubble-layer region was developed to predict the bubble-layer thickness of the subcooled boiling flow. The obtained model was evaluated by void fraction profile measured in an internally heated annulus. It was shown that the bubble-layer thickness model could be applied to predict the bubble-layer thickness as well as the void fraction profile. In addition, the constitutive equation for the distribution parameter of the boiling flow in the internally heated annulus, which was used for formulating the bubble-layer thickness model, was developed based on the measured data. The model developed in this study will eventually be used for the development of reliable constitutive relations, which reflect the true transfer mechanisms in subcooled boiling flows