Study of the bubble characteristics and the local void fraction in subcooled flow boiling using digital imaging and analysing techniques

2002 ◽  
Vol 26 (2-4) ◽  
pp. 147-155 ◽  
Author(s):  
R. Maurus ◽  
V. Ilchenko ◽  
T. Sattelmayer
Keyword(s):  
Void Fraction ◽  
Digital Imaging ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Bubble Characteristics

Modeling of Bubble Behavior in Low Void Fraction Subcooled Flow Boiling

2018 ◽  
Author(s):  
Shintaro Sakamoto ◽  
Hiroki Ohori ◽  
Koji Enoki ◽  
Tomio Okawa
Keyword(s):  
Void Fraction ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Vertical Direction ◽  
Bubble Behavior ◽  
Lateral Direction ◽  
Subcooled Flow Boiling ◽  
Accurate Evaluation ◽  
Subcooled Flow ◽  
Lift Off

In predicting the void fraction in subcooled flow boiling, accurate evaluation of single bubble behaviors is of considerable importance. In particular, bubble lift-off velocity affects the void fraction significantly since the bubble disappear quickly due to heat transfer with subcooled liquid if the lift-off velocity is high. In this study, the process of bubble lift-off was experimentally investigated to develop mechanistic correlations for the bubble lift-off velocity. In the development of the correlations, it was assumed that the bubble lift-off velocity in the horizontal direction is proportional to the bubble growth rate and that in the vertical direction is determined primarily by the local liquid velocity evaluated at the bubble center position. Then, impact of the bubble lift-off velocity on the void fraction was explored through numerical simulations. In the simulations, the bubble lift-off velocity in the lateral direction was parametrically changed. It was shown that the mean void fraction decreases with an increase in the lateral bubble lift-off velocity since the bubble condensation is enhanced. It was therefore confirmed that accurate evaluation of the bubble lift-off velocity is important for high accuracy prediction of the void fraction.

Numerical Simulation of Subcooled Flow Boiling Using a Bubble Tracking Method

2016 ◽  
Author(s):  
Tomio Okawa ◽  
Naoki Miyano ◽  
Kazuhiro Kaiho ◽  
Koji Enoki
Keyword(s):  
Numerical Simulation ◽  
Size Distribution ◽  
Void Fraction ◽  
Bubble Size ◽  
Flow Boiling ◽  
Bubble Nucleation ◽  
Bubble Size Distribution ◽  
Subcooled Flow Boiling ◽  
Tracking Method ◽  
Subcooled Flow

The process of bubble nucleation in subcooled flow boiling was visualized using a high speed camera to show that the bubble size can be significantly different between the nucleation sites. However, the bubble size is usually assumed constant in the numerical simulation of subcooled flow boiling. To explore the effect of the bubble size distribution on the void fraction in subcooled flow boiling, numerical simulations were performed using a bubble tracking method in which the size and position of each bubble are calculated individually using a Lagrangian coordinates. In the present simulation, the void fraction was greater when the bubble size distribution was taken into consideration. Since the bubble tracking method requires many correlations, further improvement is necessary. The present numerical results however indicate that the bubble size distribution should be taken in to consideration to evaluate the void fraction in subcooled flow boiling accurately.

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