Single bubbles rising in a confined geometry – a parallelepidic bubble column with a 4 mm thickness – in the presence of a non-Newtonian liquid phase are studied using a shadowgraphy technique. The context is the cultivation of microalgae at high cell concentrations. In fact, it necessitates the reduction of the bioreactor thickness to allow light penetration through the whole culture. In the same time, the medium becomes shear-thinning for biomass concentrations higher than 30 g L⁻¹. A 2 g L⁻¹ carboxymethyl cellulose (CMC) and a 1 g L⁻¹ Xanthan Gum (XG) aqueous solutions are studied to mimic the behavior of 42 g L⁻¹ Chlorella vulgaris cultures. Besides, a comparison with water, representing the Newtonian liquid phase at low culture concentrations, is proposed. The bubble equivalent diameter is varied between 1.34 and 3.36 mm using different capillary sizes to generate the bubbles. Results show the complex and coupled effects of confinement and shear-thinning behavior of the liquid phase on bubbles terminal velocity, shape and trajectory. In fact, compared to the case of an infinite liquid medium, confinement increases wall friction on the bubbles, while reduces the liquid phase apparent viscosity in its neighborhood due to increased shear rate. This is why, depending on the bubble size, the bubble terminal velocity in shear-thinning fluids can be higher or lower than in unconfined conditions. For bubbles rising in shear-thinning fluids, contrary to water, it is observed that confinement induces a transition from spherical shape to ellipsoidal shape that occurs sooner in terms of bubbles diameter or Eo number. A correlation for the bubble drag coefficient in confined conditions in presence of shear-thinning fluids is also proposed for confinement ratios d_b/e between 0.34 and 0.84.

使用影印技术研究了在非牛顿液相存在下，在有限的几何形状中上升的单个气泡（厚度为4 mm的平行四面体气泡柱）。背景是在高细胞浓度下培养微藻。实际上，必须减小生物反应器的厚度以允许光穿透整个培养物。同时，当生物质浓度高于30 g L ^-1时，介质会变稀疏。研究了2 g L ^-1羧甲基纤维素（CMC）和1 g L ^-1的黄原胶（XG）水溶液，以模拟42 g L ^-1的 小球藻的行为文化。此外，提出了与水的比较，水代表低培养物浓度下的牛顿液相。使用不同的毛细管尺寸以产生气泡，气泡当量直径在1.34和3.36 mm之间变化。结果表明，液相的约束和稀化稀疏行为对气泡的终极速度，形状和轨迹具有复杂的耦合作用。实际上，与无限液体介质的情况相比，限制会增加气泡上的壁摩擦力，同时由于增加的剪切速率而降低其附近的液相表观粘度。这就是为什么根据气泡大小，剪切稀化流体中气泡终端速度可能高于或低于无约束条件时的原因。对于在剪切稀化流体中上升的气泡（与水相反），观察到，就气泡直径或Eo数而言，限制引起从球形到椭圆形的过渡，该过渡发生得更快。对于约束比d，还提出了在存在稀疏剪切流体的约束条件下，气泡阻力系数的相关性。_b / e在0.34和0.84之间。