Shripad T. Revankar

Local interfacial area measurement in bubbly flow

Abstract A theoretical foundation of the measurement method for the time averaged local interfacial area using a double sensor probe is presented. Experimental data are presented on the radial profiles of the void fraction, bubble velocity, bubble chord length and interfacial area concentration at various gas flow rates. In addition to these, some statistical information on turbulent motions of bubbles are presented. Each of the double sensors is checked against the global void measurement using a differential pressure. The result is very satisfactory. Furthermore, the area averaged void fraction and the interfacial area concentration obtained from the double sensor probe measurement compared very well with the photographic measurements. The results show that the double sensor probe method is accurate and reliable for the local measurements of interfacial area and void fraction in bubbly two-phase flow. Some results of the measurement of interfacial area concentration with the double sensor probe are also presented for bubbly flow at different liquid flow rates.

Theory and measurement of local interfacial area using a four sensor probe in two-phase flow

Abstract A theoretical foundation of the measurement method for the time averaged local interfacial area using a four sensor resistivity probe is presented. Based on this theory, the four sensor resistivity probe was developed and employed to measure the interfacial velocity, local interfacial area concentration and void fraction in a vertical air-water cap bubbly flow. The four sensor probe measurements were checked against the global void measurement using a differential pressure. The results were very satisfactory. Theoretical profiles of the void fraction and interfacial area concentration were obtained using the pictures of cap bubbles. The theoretical predictions of the cap bubbles and the interfacial area concentration profiles compared very well with the four sensor data.

The three-level scaling approach with application to the Purdue University Multi-Dimensional Integral Test assembly (PUMA)

Abstract The three-level scaling approach was developed for the scientific design of an integral test facility and then it was applied to the design of the scaled facility known as the Purdue University Multi-Dimensional Integral Test Assembly (PUMA). The NRC Technical Program Group for severe accident scaling developed the conceptual framework for this scaling methodology. The present scaling method consists of the integral system scaling, whose components comprise the first two levels, and the phenomenological scaling constitutes the third level of scaling. More specifically, the scaling is considered as follows: (1) the integral response function scaling, (2) control volume and boundary flow scaling, and (3) local phenomena scaling. The first two levels are termed the top-down approach while the third level is the bottom-up approach. This scheme provides a scaling methodology that is practical and yields technically justifiable results. It ensures that both the steady state and dynamic conditions are simulated within each component, and also scales the inter-component mass and energy flows as well as the mass and energy inventories within each component.

Axial development of interfacial area and void concentration profiles measured by double-sensor probe method

Abstract Interfacial area concentration is an important parameter in modeling the interfacial transfer terms in the two-fluid model. In this paper, the local geometric and statistical characteristics of upward co-current dispersed bubbly flow in a pipe have been studied both at the entrance ( L D = 8 ) and at a region far away from the entrance ( L D = 60 ). The test section was a 5.08 cm i.d. and 375 cm long Lucite pipe. Four liquid flow rates ranging from 0.1 to 1.0 m s −1 were used in combination with four different gas injection rates ranging from 0.02 to 0.1 m s −1 . A double-sensor probe was employed to measure the radial profiles of void fraction, interfacial area concentration, Sauter mean diameter, bubble velocity and bubble frequency. The wall peak of the void fraction profile was established within a short distance from the entrance. The flow characteristics changed very little from the entrance region to the fully developed region except for the flow case of j 1 = 0.1 m s −1 . The area averaged flow quantities were also presented.

Modeling and Measurement of Thermal Properties of Ceramic Composite Fuel for Light Water Reactors

The thermal modeling of a composite fuel consisting of continuous second phase in a ceramic (uranium oxide) matrix has been carried out with aid of detailed examination of the microstructure of the composite and the interface structure. BeO and SiC were considered as second phase dispersed in UO2 matrix by weight from 0–15% to enhance the thermal conductivity. It is found that with 10% SiC, the thermal conductivity increases from 5.8 to 9.8 W/m-K at 500 K. A finite element analysis computer program ANSYS was used to create composite fuel geometries with set boundary conditions to produce accurate thermal conductivity predictions. The results were compared to analytical calculations as previously performed with the series geometry to verify the validity of using ANSYS in producing accurate thermally enhanced nuclear fuel models. Good agreement was found between experimental measured thermal conductivity for BeO-UO2 matrix and the model predictions.

Analysis of flow instabilities and their role on critical heat flux for two-phase downflow and low pressure systems

A stability analysis of a flow boiling two-phase low pressure and downflow system relative to the occurrence of critical heat flux has been carried out. The problem formulation is based on a time and area averaged one-dimensional drift flux model, with the necessary constitutive equations. A characteristic equation is obtained to predict the onset of flow excursion and density wave oscillations. By non-dimensionalizing the characteristic equation, important groups governing the system stability are determined. The results of the analysis are useful in determining the region of stable operation for downflow in the Westinghouse Savannah River Site Reactor and in avoiding the onset of flow excursions and density wave oscillations. The analytical results for flow excursion are compared with the Babcock and Wilcox flow excursion experimental data with a Savannah River Mark 22 fuel assembly mockup.

Enhanced Thermal Conductivity Oxide Fuels

the purpose of this project was to investigate the feasibility of increasing the thermal conductivity of oxide fuels by adding small fractions of a high conductivity solid phase.

Transient Analysis of Sulfur-Iodine Cycle Experiments and Very High Temperature Reactor Simulations Using MELCOR-H2

Abstract MELCOR is a thermal-hydraulic code used by the United States and the international nuclear community for the modeling of both light water and gas-cooled reactors. MELCOR was extended in order to model nuclear reactors that are coupled to the sulfur-iodine (SI) cycle for cogeneration of hydrogen. This version of the code is known as MELCOR-H2, and it includes modular secondary system components (e.g., turbines, compressors, heat exchangers, and generators), a point-kinetics model, and a graphical user interface. MELCOR-H2 allows for the fully coupled, transient analysis and design of the nuclear thermochemical SI cycle for the purpose of maximizing the production of hydrogen and electricity. Recent work has demonstrated that the hydrogen generation rate calculated by MELCOR-H2 for the SI cycle was within the expected theoretical yield. In order to benchmark MELCOR-H2, we simulated a set of sulfuric acid decomposition experiments that were conducted at Sandia National Laboratories during 2006. We also used MELCOR-H2 to simulate a 2004 Japan Atomic Energy Research Institute SI experiment. The simulations compared favorably with both experiments; most measured and calculated outputs were within 10%. The simulations adequately calculated O2, SO2, and H2 production rate, acid conversion efficiency, the relationship between solution mole percent and conversion efficiency, and the relationship between molar flow rate and efficiency. We also simulated a 6-stage turbine and a 20-stage compressor. Our results were mostly within 1 or 2% of the literature. Then, we simulated a pebble bed very high temperature reactor (VHTR) and compared key MELCOR-H2 results with the literature. The comparison showed that the results were typically within 1 or 2%. Finally, we compared the MELCOR-H2 point-kinetics model with the exact Inhour reactivity solution for various cases, including a 1.0

Thermal Stratification and Mixing in an Open Water Pool by Submerged Mixtures of Steam and Air

step reactivity insertion. We were able to employ a large time step while successfully matching the theoretical power level. These comparisons demonstrate MELCOR-H2’s unique ability to simulate fully coupled VHTRs for the production of hydrogen.

Thoria-based cermet nuclear fuel : cermet fabrication and behavior estimates.

Phenomena associated with jet-plume condensation of steam-air mixtures in a large subcooled pool of water have implications in predicting global system parameters, such as the containment pressure, in light water reactors. A scaled down, reduced pressure suppression pool was designed to study condensation and mixing phenomena using scaled test conditions obtained from RELAP5 code results of a loss of coolant accident in a simplified boiling water reactor. Results from the experiments were compared with the TRACE code predictions which reveal deficiencies in the code to predict the pool thermal stratification as TRACE was not initially developed for predicting such phenomena. A dimensionless boundary map was plotted from several experimental runs of pure steam injection to determine conditions when the pool transits from being a homogeneously mixed volume to being a thermally stratified one. Steam-air mixture injection cases for single horizontal venting indicated that above a pool temperature of 40 °C with air mass flow rates below 0.1 g/s the pool can attain thermal stratification.Copyright