Session: 07-07: Experiments and Analyses - VI

Paper Number: 134244

134244 - Experimental Investigation on Void Fraction Measurement in High-Temperature and High-Pressure Gas-Liquid Two-Phase Flow 

Abstract: 

In nuclear power plants, gas-liquid two-phase flow can be occurred under high pressure and high temperature conditions. To understand and predict such kind of two-phase flow behavior, it is necessary to measure the void fraction distribution in experiment under the high pressure and high temperature condition.
However, few studies have been done on local void fraction measurement under high pressure and high temperature conditions up to the saturation condition at approximately 13MPa(abs). In such a high-pressure condition, bubble diameter is considered very small due to the high pressure and the diameter is assumed to be approximately 100 to 150 micrometres.
Air-water vertical upward two-phase flow experiment was carried out to evaluate accuracy of the void fraction measurement and to observe bubble behavior hitting to the sensor tip. An optical probe with the tip diameter of 125 micrometres was tested. In this experiment, a bubble generator made of porous ceramic was utilized to generate small bubbles with the diameter of around 150 micrometres. Surfactant is also used to inhibit bubble coalescence and to make small bubbles flow into the test section without coalescence. Two types of test sections were utilized in this study. One is thin rectangular duct with the cross section of 10 mm x 49 mm and the other is a circular pipe with inner diameter of about 25 mm. The duct section is for visualization and the pipe section is for quick closing valve measurement.
Simultaneous measurement of visualization and voltage signal acquisition was conducted and the relationship between the voltage signal response of the probe and the bubbles hitting to the probe tip in the recorded pictures was investigated. In the two-phase flow with small bubbles, the voltage signal responses are small compared to those obtained in two-phase flow contains larger bubbles.
Locally measured void fraction was area-averaged in the cross-section and compared with the void fraction measured by quick closing valve method, which corresponds to volume-averaged void fraction. From this kind of comparison, the accuracy of probe measurement was evaluated. In the void fraction calculation process, a modified method has been developed for the voltage signal obtained in two-phase flow with small bubbles. Since the voltage signal response is small in such a two-phase flow with small bubbles, the modified procedure was developed in this study to distinguish such a small response of gas phase from the liquid phase voltage signal.
It is confirmed that the optical probe tested in this study has high detectability of small bubbles with a diameter around 150 micrometres due to its thin tip and the probe has high accuracy in void fraction measurement for two-phase flow with such small bubbles.

Presenting Author: Hiroaki Nakanishi Mitsubishi Heavy Industries, Ltd.

Presenting Author Biography: Hiroaki Nakanishi is an employee of Mitsubishi Heavy Industries, Ltd. His work focuses on multi-phase flow.

Authors:

Yoshiteru Komuro Mitsubishi Heavy Industries, Ltd.
Hiroaki Nakanishi Mitsubishi Heavy Industries, Ltd.
Seiho Utsumi Mitsubishi Heavy Industries, Ltd.
Yoshiyuki Kondo Mitsubishi Heavy Industries, Ltd.
Takashi Ueno Mitsubishi Heavy Industries, Ltd.