Nonlinear Dynamics of Gas-Liquid Separation in a Capillary Microseparator
Nonlinear Dynamics of Gas-Liquid Separation in a Capillary Microseparator
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毛细管微分离器中气液分离的非线性动力学
DOI：
10.1115/icnmm2018-7613
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Radhakrishnan A
中科院分区：
文献类型：
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作者：
Radhakrishnan A
微工程设备（MED）在执行分离过程中正在显着增长1。这种装置已经在从化学催化反应器到产品纯化系统（如微蒸馏）的一系列应用中实施。这些装置的最大优点之一是毛细作用和界面张力的优势。MED已被使用的领域是气液分离。例如，在化学反应器之后会遇到这些问题，其中产生的气体组分需要立即从反应器中去除，因为它会影响后续反应。气相可以有效地去除使用MED与微毛细管阵列。然后可以以受控的方式沿着这些毛细结构沿着进行相分离。对于由亲水性材料（例如Si或玻璃）制成的装置，由于毛细管压力，润湿相（例如水）流过毛细管，而非润湿分散相（例如气体）被阻止进入毛细管。液-液流的分离也可以通过这种方法实现。然而，相分离的基本机制远未被完全理解。气相进入毛细管时的压力（气液突破）可通过杨-拉普拉斯方程估算，该方程由湿相的表面张力（γ）、毛细管宽度（d）和高度（h）以及界面平衡接触角（θeq）决定。类似地，液体到气体的突破压力（即，完全液体分离停止并且液体通过气体出口离开的点）可以通过哈根-普瓦勒（HP）方程从毛细管两端的压降估计。几个组报告了偏离这些估计值的情况，因此纳入了各种参数以说明偏离情况。这些参数通常说明（i）湿相通过“n”个平行毛细管的流动，（ii）Mortensenet等人的几何校正因子的修改，20052和（iii）分离过程中的液体段塞长度（LS）和毛细管数（n）AS已经在毛细管区的上游测量或根据Garbanki等人提出的标度定律估计，20063.然而，这种方法没有解决表观入口速度和通过每个毛细管的液体净流出量（qc）之间的平衡。这些模型的另一个缺点是对表观接触角（θapp）的估计，这在预测液体到气体突破中起着关键作用。假设θ app等于θ eq，或使用各种技术测量，例如通过毛细管上升或平坦基底上的静态液滴，这与分离期间的实际动态接触角显著不同。在其他情况下，Cox-Voinov模型已被用于从θ eq和毛细管数计算θ app。因此，文献中可用的经验模型不能以足够的精度预测现实的突破压力。因此，有必要对分离过程中的临界液塞特性进行更详细的现场研究。在这里，我们报告的进步，在气液分离（GLS）设备中的两相分离的基本理解，通过一个理论模型开发的基础上发生在分离过程中的气液界面的关键事件。
Micro-engineered devices (MED) are seeing a significant growth in performing separation processes1. Such devices have been implemented in a range of applications from chemical catalytic reactors to product purification systems like microdistillation. One of the biggest advantages of these devices is the dominance of capillarity and interfacial tension forces. A field where MEDs have been used is in gas-liquid separations. These are encountered, for example, after a chemical reactor, where a gaseous component being produced needs immediate removal from the reactor, because it can affect subsequent reactions. The gaseous phase can be effectively removed using an MED with an array of microcapillaries. Phase-separation can then be brought about in a controlled manner along these capillary structures. For a device made from a hydrophilic material (e.g. Si or glass), the wetted phase (e.g. water) flows through the capillaries, while the non-wetted dispersed phase (e.g. gas) is prevented from entering the capillaries, due to capillary pressure. Separation of liquid-liquid flows can also be achieved via this approach. However, the underlying mechanism of phase separation is far from being fully understood. The pressure at which the gas phase enters the capillaries (gas-to-liquid breakthrough) can be estimated from the Young-Laplace equation, governed by the surface tension (γ) of the wetted phase, capillary width (d) and height (h), and the interface equilibrium contact angle (θeq). Similarly, the liquid-to-gas breakthrough pressure (i.e. the point at which complete liquid separation ceases and liquid exits through the gas outlet) can be estimated from the pressure drop across the capillaries via the Hagen-Poiseuille (HP) equation. Several groups reported deviations from these estimates and therefore, included various parameters to account for the deviations. These parameters usually account for (i) flow of wetted phase through ‘n’ capillaries in parallel, (ii) modification of geometric correction factor of Mortensenet al., 20052and (iii) liquid slug length (LS) and number of capillaries (n) during separation.LShas either been measured upstream of the capillary zone or estimated from a scaling law proposed by Garsteckiet al., 20063. However, this approach does not address the balance between the superficial inlet velocity and net outflow of liquid through each capillary (qc). Another shortcoming of these models has been the estimation of the apparent contact angle (θapp), which plays a critical role in predicting liquid-to-gas breakthrough. θappis either assumed to be equal to θeqor measured with various techniques, e.g. through capillary rise or a static droplet on a flat substrate, which is significantly different from actual dynamic contact angles during separation. In other cases, the Cox-Voinov model has been used to calculate θappfrom θeqand capillary number. Hence, the empirical models available in the literature do not predict realistic breakthrough pressures with sufficient accuracy. Therefore, a more detailedin situinvestigation of the critical liquid slug properties during separation is necessary. Here we report advancements in the fundamental understanding of two-phase separation in a gas-liquid separation (GLS) device through a theoretical model developed based on critical events occurring at the gas-liquid interfaces during separation.