Oxygen transfer from bubble-plumes

Abstract

Air-bubble plumes produced beneath ocean breaking waves have important roles in gas transfer between atmosphere and ocean because the gas within the bubbles, convected by breaking-waveinduced turbulence, is dissolved at a deeper level. In particular, oxygen dissolution supports all biological activities in a marine ecosystem. Oxygen transfer from bubbles to bulk water depends on the dynamics of local bubble flows. As lateral bubble motion associated with vortex wakes generates turbulence in the ambient fluid, depending on the bubble size, the dissolved gas in the plume is transported via complex convection and diffusion processes. Although analytical and empirical models of gas transfer from a small, rigid bubble have been proposed previously, the effects of bubble size on gas concentrations in the turbulence field remain poorly understood. In this study, we examine the explicit effects of bubble size on bubble plume turbulence and the dissolved oxygen (DO) concentration field, and propose a new empirical gas transfer model that is applicable to large deformable bubbles on the basis of experimental imaging analysis. The gas transport process in the plume was identified using bubble turbulence coupled flow computations with the proposed gas source model, which well explained the variation in experimental DO concentration. The proposed transfer velocity model extended the applicable bubble size range and predicted the major features of the increasing oxygen concentration within the plume. We expect these findings to serve as a starting point to improve our understanding of the dynamics of practical bubble plume flows with wider bubble size ranges, as typically formed under breaking waves, and to predict oxygen concentrations in marine environments.

Kinetic Behaviors of Methane Hydrate Formation with Bubble Seeping at Conditions of “Haima” Cold Seep

“…The enhancement of plume effect would facilitate dissolution of gas molecules in water. 29 Hence, when the plume effect was enhanced, i.e., the number of bubbles across water increased per unit time with the increase of methane flux, the CH 4 molecules transfer from the bubble interface into the water became accelerated. Besides, the bubbles would break up once they raised to the gas−liquid interface at the top of the cell.…”

“…For example, the bubbles rising was a steady-state process for Run A1 (Figure a) at such a low methane flux (0.002 mol/min) that the bubbles rised independently with a negligible bubble–bubble plume effect. The enhancement of plume effect would facilitate dissolution of gas molecules in water . Hence, when the plume effect was enhanced, i.e., the number of bubbles across water increased per unit time with the increase of methane flux, the CH 4 molecules transfer from the bubble interface into the water became accelerated.…”

気泡の水面への浮上を通した、気泡-乱れ、気泡-水面、気泡-気泡相互作用

“…海洋波浪が海岸へと伝播するとき、浅水変形に よって発達した波峰は前方に放出され波面前方 に着水する(砕波と呼ぶ) 。これに押し出されて 跳ね上がった二次ジェットが次々と着水を繰り 返す砕波過程を経て(Fig. 1) 、砕波帯には大規模 な組織渦構造が形成される [1]。 同時に海中に混入 した大量の気泡の一部は、組織渦中に捕捉され長 時間海中に滞留し、気泡界面を介した海中への気 体輸送を通じて海洋生態系が維持される [2]。 海中 から浮上した気泡群は砕波背後で凝集し、長期間 に渡って海面上に滞在し気体輸送に加え海洋生 物活動をサポートする(Fig. 1) 。この砕波に伴い 生成される水面上を覆う気泡群は、その視覚的特 徴から白波と呼ばれ、海洋画像観測において砕波 発生の指標として扱われ、また白波の相対専有面 積を白波被覆率として砕波によるエネルギー散 逸 [3]、大気-海洋間運度量輸送 [4]および気体輸送 [5]の予測パラメータとして利用されてきた。 一方、…”