Stanford University, Energy Sciences and Engineering, 367 Panama St, room 50, Stanford, California, USA.
Lab Chip. 2022 Sep 13;22(18):3489-3498. doi: 10.1039/d2lc00595f.
We designed and fabricated a new microfluidic device to better enable study of foam microstructure and rheology in planar fractures. The design phase included stress-strain finite element analysis to enhance the pressure tolerance of the device. The optimized design is a 2 cm wide by 7.75 cm long rough fracture that includes 25 posts to anchor the glass cover plate. The posts simulate asperities and provide structural support during bonding of a glass cover plate to the device. Importantly, the new design illustrates improved ability to sustain large differential pressure compared to previous designs in the literature. The rheometer permits study of the relationship among foam bubble morphology, pressure drop, and flow rates. Our findings validated the previous, sparse microvisual studies mentioned in the literature and confirmed that small quality foam, ranging from 20 to 50% gas by volume, contains dispersed bubbles separated by liquid lenses. In this range, the distribution of bubble sizes was roughly 80-90% small uniform bubbles and only 10-20% of larger and more elongated bubbles. Additionally, our studies reveal that foam apparent viscosity is a strong function of foam quality, velocity, and texture (, bubble size). Apparent viscosity of foam ranged from 100 to 600 cP for the conditions studied. High quality foams in fractures are independent of gas flow rates but very sensitive to liquid flow rates. On the other hand, low quality foams are sensitive to gas flow rates but independent of liquid flow rates.
我们设计并制造了一种新的微流控装置，以更好地研究平面裂缝中的泡沫微观结构和流变学。设计阶段包括应力-应变有限元分析，以提高装置的耐压能力。优化设计是一个 2 厘米宽、7.75 厘米长的粗糙裂缝，其中包括 25 个柱子以固定玻璃盖板。这些柱子模拟了粗糙度，并在将玻璃盖板粘合到装置上时提供结构支撑。重要的是，与文献中的先前设计相比，新设计展示了提高承受大压差能力。流变仪允许研究泡沫泡形态、压降和流速之间的关系。我们的研究结果验证了文献中提到的先前稀疏的微观视觉研究，并证实了小质量泡沫（体积比为 20%至 50%的气体）包含由液体透镜分隔的分散气泡。在这个范围内，气泡尺寸的分布大致为 80-90%的小均匀气泡，只有 10-20%的较大和更长的气泡。此外，我们的研究还表明，泡沫表观粘度是泡沫质量、速度和结构（气泡尺寸）的强函数。在所研究的条件下，泡沫的表观粘度范围为 100 至 600 cP。裂缝中的高质量泡沫独立于气体流速，但对液体流速非常敏感。另一方面，低质量泡沫对气体流速敏感，但对液体流速不敏感。
