Experimental study of seismic vibration effect on two-phase flow.

摘要

This study is to investigate the seismic vibration effects on two-phase flow. Based on the seismic characteristics found in literature, the properties for designing a test facility to simulate vibration and the test conditions for adiabatic and diabatic (subcooled boiling) two-phase flows have been chosen. In order to perform this experiment, an annulus test section has been built and attached to a vibration module. For experimental investigation and visualization of two-phase flow, Pyrex-glass tubes have been utilized as a transparent test section and stainless steel instrumentation ports are designed to acquire experimental data. In the design process, calculations considering the resonance, natural frequency, structural deflection, material properties and vibration conditions for the vibration structure have been performed to choose a suitable vibration beam. The motion equations of the eccentric cam are also analyzed with respect to displacement (vibration amplitude), velocity and acceleration. Each design process is set for the goal of an economical, reliable and controllable vibration condition for the two-phase flow test section. In addition, the scaling laws for geometric similarity, hydrodynamic similarity and thermal similarity are taken into account for the annulus test section to simulate a fuel assembly sub-channel of a prototypic boiling water reactor (BWR).;Potential hydrodynamic and thermal effects for two-phase flow under seismic vibration are broken down and analyzed in detail. Based on the 1-D drift-flux model, the hydrodynamics effects are discussed with respect to the possible variations of distribution parameters, C0, and drift velocity, nugj, caused by the changes of the void distribution, bubble diameter and flow regimes. Sensitivity studies are carried out for analyzing these potential hydrodynamic effects. In addition, the void generation relations in a diabatic (subcooled boiling) two-phase flow system are taken into account for analyses of potential thermal effects, including the onset of nucleate boiling and onset of significant void (ONB-OSV) effect, wall nucleation effect and bulk phase change effect. Analyses of phenomenological changes and temperature distributions are performed for estimations of void changes due to vibration.;An extensive 1-D experimental database is assembled for adiabatic and subcooled boiling two-phase flow under stationary and vibration conditions. The adiabatic test results are used to examine and verify the potential hydrodynamic effects, whereas the subcooled boiling test results are compared and explained by proposed thermal effects. Several vibration effect maps were made in terms of flow conditions (jg>-j f> ), thermal conditions (NZu-N Sub), operation conditions (j f>-alpha>) and vibration conditions ( E-f and f-alpha) for adiabatic and subcooled boiling two-phase flow tests. Among these vibration effect maps, different effective vibration conditions and dominant effects can be seen by regions. In the jg>- jf> plots of adiabatic two-phase flow tests, the hydrodynamic effect is found to dominate. The void fraction is found to potentially decrease due to vibration in wall-peak bubbly flow regime and increase at the region close to bubbly-to-slug transition boundary. No significant change in void fraction is found in slug flow regime under vibration. In addition, the thermal effect due to vibration is presented on the NZu- NSub plots. Three regions representing void increase, no change and void decrease which are corresponding to thick thermal boundary layer (TBL), bulk saturation and near saturation with low flow and high subcooling conditions are presented for subcooled boiling flow under seismic vibration. Finally, the E-f and f- alpha plots express the effective vibration conditions for adiabatic and subcooled boiling flows, and the acceleration values are compared with existing earthquake intensity records. In summary, a systematic database covering wide ranges of seismic vibration conditions along with adiabatic/diabatic flow/thermal conditions has been built in this study, and the physical understanding of seismic vibration effect on two-phase flow has been developed based on the analyses of potential hydrodynamic and thermal effects. Several vibration effect maps on different planes have been proposed as important conclusions for seismic vibration effects on two-phase flow systems.