High-Resolution X-Ray Radiography Methods Developed for Post-CHF Experiment

Radiation transmission measurement methods have become widely implemented in the study of two-phase flow due to leaping advancements in detector efficiency, spatial resolution, and high-speed measurement capabilities. However, radiation-based measurements of boiling experiments bear several challenges due to the mismatch of calibration to experimental conditions, beam hardening, thermal expansion, and material and working fluid density changes with temperature. The present research focuses on developing methods to analyze the high-resolution X-ray radiography measurements of the post-critical heat flux (Post-CHF) heat transfer facility built at the University of Michigan that is intended to perform high-pressure and high-temperature measurements; the experimental test section is made of Incoloy-800H and is characterized as a cylindrical geometry expanding 1.0 m in length. The broad goal of the experiment is to build a high-resolution database to develop models for inverted annular film boiling and inverted slug film boiling through dispersed flow film boiling. The methods developed in this research model the thermal effects of the postulated challenges in order to properly scale the X-ray calibration measurements to the experimental conditions. Additionally, a cross-section-weighted method is developed to estimate the axial void fraction; this method is validated by modeling the test section with synthetic void fraction data. Last, preliminary high-speed X-ray measurements performed at subcooled boiling conditions are presented and analyzed with the developed methods, which include bubbly, slug, and churn flows.