A strategy for regulation of gas–liquid microflow patterns by changing gas kinetic energy

General prediction models for void fraction and specific surface area of gas–liquid microflows

“…In this work, we first studied the variations of the bubble size in different T‐junctions. Figure 2A indicates that the method that changes the capillary inner diameter of the T‐junction is an efficient tool to control the bubble with desired size, 32 which gives the opportunity to explore the influence of the bubble size on the value of α when the operating parameters are the same. Figure 2B shows the variations between the α value and the liquid flow rate ( Q L ) and bubble size, and the calculation method of the void fraction can be found in the Supplementary material.…”

“…To find out the abnormal results in Figure 2, in this section, we first studied the gas–liquid microflow state in each microreactor, as presented in Figure 4. The flow pattern is Taylor flow in T‐junction‐1/−2, short bubble or bubbly flow in T‐junction‐3/−4, 32 and bubble swarm flow in T‐junction‐5/−6. In other words, different gas–liquid flow patterns may be the inherent reason behind the two different trends of the relative size of the void fraction in T‐junction‐2 and T‐junction‐3 in Figure 2B.…”

“…Therefore, the bubble flow velocity in T‐junction‐4 is faster than that in T‐junction‐3, and the α value in T‐junction‐4 is less than the α value in T‐junction‐3 according to Equation (). Second, during the bubble formation stage, the maximal bubble neck width is positively correlated with the bubble size under the same gas–liquid flow rates, 32 which means that the gas blocking degree will be decreased in T‐junction‐4 and more liquid phase will be leaked between the bubble body and channel wall. Therefore, a longer liquid slug or thicker liquid film will exist and the void fraction is decreased in T‐junction‐4.…”

“…33 That is to say, a thinner liquid film is beneficial to reduce fluid leakage and increase the void fraction, and the liquid film thickens when the velocity increases. 34 Via the velocity field measurement technology, van Steijn et al 35 rates, 32 which means that the gas blocking degree will be decreased in T-junction-4 and more liquid phase will be leaked between the bubble body and channel wall. Therefore, a longer liquid slug or thicker liquid film will exist and the void fraction is decreased in T-junction-4.…”

“…However, we can find that 2) is proposed, and the fitting parameters are listed in Table 3. The parameter of bubble equivalent diameter is determined by the microdispersion structure and can be calculated from the existing models, such as bubble length, 40,41 bubble diameter, 42,43 and bubble generation frequency, 11,32 and the Ca number (Ca = μu L /σ) is determined based on the liquid superficial velocity (u L , the ratio of the liquid flow rate to the cross-sectional area of the channel) in the bubble flow channel. Figure 7A indicates that this new equation type for the void fraction can predict the result for the four different gas-liquid flow patterns well within ±15%.…”