应实验室邀请，弗吉尼亚理工大学Prof. Yang Liu 访问实验室并为实验室师生做学术讲座。敬请实验室相关方向师生积极准备参加。
讲座题目：Advanced Measurement Techniques for Gas-Liquid Two-Phase Flow
Accurate measurement of gas-liquid two-phase flow has been a challenging task for many decades due to complex interfacial structure existing in such flows. However, high-quality and high-resolution two-phase flow data is important for developing and validating advanced models which have become essential tools for various engineering applications. In this talk, several techniques recently developed to tackle this challenge will be introduced. The first technique is based on a high-speed optical imaging system and advanced image processing algorithms. A comprehensive image processing package has been developed to deal with issues such as separation of overlapping bubbles, 2-D outline reconstruction, 3-D shape reconstruction, bubble tracking, and identification of bubble interaction mechanisms. Time-resolved 3-D bubble information could be obtained using this method for low void fraction bubbly flows. The second technique is based on a fast X-ray densitometer system. High resolution linear detector arrays are used in this system, which could yield direct void fraction measurement along the X-ray beam path. Several practical issues such as X-ray energy spectrum will be discussed. The third technique is based on PIV (Particle Image Velocimetry) and PLIF (Planar Laser Induced Fluorescence), which has been developed to measure the liquid-phase velocity and turbulence characteristics. In this system, fluorescent particles are used to seed the liquid flow and an optical phase separation method is adopted to remove the bubbles recorded on the PIV images. The last topic introduced here is about the uncertainty quantification of the multi-sensor conductivity probe. In this study, the uncertainty sources involved in probe fabrication, signal processing, and measurement models are integrated into a single framework based on the Monte Carlo method. The uncertainty of a practical measurement can be predicted by this framework based on the specific measuring parameters such as test section dimension, measuring location, probe configuration, flow condition, bubble size, shape and velocity fluctuation. It is expected that various two-phase flow regimes can be measured more accurately with these newly developed measurement techniques.
Dr. Yang Liu is an assistant professor of the Mechanical Engineering Department at Virginia Tech. Prior to his current position, he was a postdoctoral research associate in the Thermal-hydraulics and Reactor Safety Laboratory at Purdue University. His research interests include nuclear reactor thermal hydraulics, multiphase flow and heat transfer, fast X-ray densitometry, and high speed optical imaging, etc. He severs on the executive committee of the thermal-hydraulics division of the American Nuclear Society. He has authored/co-authored more than 70 research publications in international journals and conferences. Dr. Liu received his B.S. in 2000, M.S. in 2003 from Shanghai Jiao Tong University, and his Ph.D. in 2008 from Purdue University, all in nuclear engineering.