Abstract:

Two kinds of anisotropic and isotropic porous media microfluidic chips with transverse and longitudinal throat width ratios (w_h∶w_z) of 1.48∶1 and 1∶1 were designed. Taking CO₂ as the gas and dimethyl silicone oil as the liquid, the effect of the structure of porous media on the growth and coalescence of bubbles under the condition of elevated temperature was systematically studied by using visualization experiments. The results show that the mass transfer growth caused by temperature rise was the driving force for bubbles to break through the throat. The growth direction of a single bubble in porous media depends on the threshold pressure, and bubbles tend to break through the throat with lower threshold pressure. As the temperature increases, the speed of air bubbles invading and breaking through the throat increases. In anisotropic porous media, bubbles tend to coalesce when they grew laterally. However, in isotropic porous media, bubbles are more likely to coalesce longitudinally. The initial distribution of multiple bubbles in anisotropic porous media can significantly affect the growth and coalescence of bubbles. However, in isotropic porous media, this effect is weaker. Anisotropic porous media is easier to realize the control of multiple bubbles in practical engineering applications.

Key words: heating process, bubble, porous medium, bubble growth, bubble coalescence, microfluid

摘要：

设计了两种横向和纵向喉道宽度比值（w_h∶w_z）分别为1.48∶1和1∶1的各向异性和各向同性多孔介质微流体芯片，以CO₂为气体，二甲基硅油为液体，采用可视化实验，系统地研究了升温条件下多孔介质结构对气泡生长和聚并规律的影响。结果表明，温度升高引起的传质生长是气泡突破喉道的动力。单个气泡在多孔介质内生长方向的选择依赖于喉道的门阙压力，气泡倾向于突破门阙压力小的喉道。随着温度的升高，气泡侵入和突破喉道速度加快。在各向异性多孔介质中，气泡倾向于在横向生长时与其他气泡发生聚并，而在各向同性多孔介质中，气泡更易发生纵向聚并。当多个气泡存在于各向异性多孔介质内时，气泡的初始分布会显著影响气泡间的生长和聚并过程；在各向同性多孔介质内时，影响则较小。各向异性多孔介质在实际工程应用过程中更易实现气泡流型调控。

关键词: 升温过程, 气泡, 多孔介质, 气泡生长, 气泡聚并, 微流体