Near-Wall Bubble Dynamics in Flow Boiling: Insights from Interface Capturing Simulation

Flow boiling allows achieve high heat transfer coefficients due to the combination of the forced convection process with the phase change. However, accurate modeling of this phenomenon is still a challenge. In the current work the flow behavior of HFE-301 in a vertical rectangular channel is modeled using interface capturing approach. Finite-element code PHASTA coupled with level-set method for interface capturing is utilized. To observe multiple nucleation events, nucleation cavities of varied sizes are introduced in the channel. The resulted bubble characteristics (bubble departure diameter, departure frequency and the amount of steam released) are compared against experimental data. Although the smallest cavity size considered is still much larger than the real one, it allows to observe bubble departure diameters close to the experimental values. As the cavity diameter decreases, a neck formed at the bottom of a bubble becomes narrower. Therefore, allowing smaller bubbles depart from a smaller cavity. It has been observed that as bubbles depart, they move toward the center of the channel, but then return back to the wall (bubble bouncing motion). It is noticed that smaller bubbles tend to bounce higher.