Two-phase flow characteristic of inverted bubbly, slug and annular flow in post-critical heat flux region

Abstract

Inverted annular flow can be visualized as a liquid jet-like core surrounded by a vapor annulus. While many analytical and experimental studies of heat transfer in this regime have been performed, there is very little understanding of the basic hydrodynamics of the post-CHF flow field. However, a recent experimental study was done that was able to successfully investigate the effects of various steady-state inlet flow parameters on the post-CHF hydrodynamics of the film boiling of a single phase liquid jet. This study was carried out by means of a visual photographic analysis of an idealized single phase core inverted annular flow initial geometry (single phase liquid jet core surrounded by a coaxial annulus of gas). In order to extend this study, a subsequent flow visualization of an idealized two-phase core inverted annular flow geometry (two-phase central jet core, surrounded by a coaxial annulus of gas) was carried out. The objective of this second experimental study was to investigate the effect of steadystate inlet, pre-CHF two-phase jet core parameters on the hydrodynamics of the post-CHF flow field. In actual film boiling situations, two-phase flows with net positive qualities at the CHF point are encountered. Thus, the focus of the present experimental study was on the inverted bubbly, slug, and annular flow fields in the post dryout film boiling region. Observed post dryout hydrodynamic behavior is reported. A correlation for the axial extent of the transition flow pattern between inverted annular and dispersed droplet flow (the agitated regime) is developed. It is shown to depend strongly on inlet jet core parameters and jet void fraction at the dryout point. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or othrrwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United Stales Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Hydrodynamically induced dryout and post dryout important to heavy water reactors: A yearly progress report

“…A visualization study of film boiling during transient quenching, by introducing Freon 113 into the bottom of a heated quartz test section, was carded out. It has been established that the axial flow pattern in this study consists basically of three regions, namely, rough wavy, agitated, and dispersed droplet/ligament, in agreement with the flow field observed in the steady-state, two-phase core injection experiment [31].…”

“…In the present film boiling experimental study, the post-CHF flow regimes were similar to the flow patterns established previously by Ishii and Denten [31 ]. For single-phase liquid core injection, in the steady-state experiment, the post-CHF flow field contained four basic f_w regimes: the smooth regime (stable inverted annular flow), the rough wavy regime, the agitated regime (transition flow between inverted annular and dispersed droplet flow), and the dispersed ligament/droplet regime [25].…”

“…Ishii and Dcntcn [8,31] extended the studies, reported by Ishii and co-workers [7,24,25], to investigate the axial extent and flow regime transition in an idealized inverted annular flow geometry where a two-phase liquid core is injected into the heated test section surrounded by a gas annulus. They correlated the axial extent of the agitated flow regime in the post-CHF rc#on in terms of the two-phase liquid jet Capillary number, Ca= _fjJ , and the jet theoretical The brief review presented above indicates that more effort has been recently put into the study of hydrodynamics of the post-CHF region.…”

Machine Learning Applications and Uncertainty Quantification Analysis for Reflood Tests

“…An essential aspect of this is the accurate prediction of quenching time, as once the fuel rods are quenched, they cool to natural convection levels, averting potential fuel meltdown and ensuring safety. Among the complex phenomena during reflooding, saturated film boiling (SFB) [8][9][10], dispersed flow film boiling (DFFB) [11,12], and inverted annular film boiling (IAFB) [13,14] play a pivotal role. Understanding these heat transfer processes is crucial for refining predictions and improving reactor safety analysis [15][16][17].…”