D123 Investigation of two-phase flow dynamics with discrete bubble model

Traveling void wave in horizontal two-phase flow

“…In order to simulate dynamic behavior, such as bubble coalescence, breakup, expansion and/or compression leading to flow pattern transition, it is essential to take into account momentum effects exerted on the hypothetical bubble. Such momentum effects are included as local rules, being the same as in the previous paper [5,6]. In the following sections, details of these local rules are described, while focusing on newly introduced and/ or improved items for the horizontal flow simulation.…”

“…In the following sections, details of these local rules are described, while focusing on newly introduced and/ or improved items for the horizontal flow simulation. The detailed structure of the model can be also found elsewhere [5,6].…”

“…In other words, bubbles move with expanding or compressing, even though weakly, in accordance with the local pressure, and these fluctuations of bubble, i.e. void fraction fluctuation, show substantial importance in the formation of intermittent flow pattern [5,6,11]. An inclusion of gas compressibility mechanism in local rules, as a matter of course, gives rise to an inconsistency with Eq.…”

“…The second term containing the equivalent liquid height H eq represents the static pressure difference caused by the difference in liquid heights across two successive cross-sections, and the third and fourth terms represent the scooped and shed momentums at the nose and the tail of the liquid slug, respectively. Compared with the previous paper for a vertical flow [5,6], the second to fourth terms are newly introduced in estimating the pressure difference instead of the gravitational pressure drop along the tube axis. The third and fourth terms are not limited to a horizontal flow, but are rather small compared with the gravitational pressure drop in a vertical flow.…”

“…In order to simulate instantaneous fluctuations of the void fraction and to know the statistical properties unique to each flow pattern, a pattern dynamics model has been developed by the authors based on the void-propagation equation, i.e. mass conservation equation of gas phase and a limited number of local rules representing momentum effects [4][5][6]. The developed model is referred to as ''discrete bubble model" by the authors.…”