Physics of Fluid Transport in Hybrid Biporous Capillary Wicking Microstructures.
Physics of Fluid Transport in Hybrid Biporous Capillary Wicking Microstructures.
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DOI：
10.1021/acs.langmuir.6b01611
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发表时间：
2016-08
期刊：
影响因子：
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通讯作者：
Saitej Ravi;Ramanathan Dharmarajan;S. Moghaddam
中科院分区：
文献类型：
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作者：
Saitej Ravi;Ramanathan Dharmarajan;S. Moghaddam
质量输送能力（即，均质吸液芯的毛细极限受到毛细压力和渗透率之间的反比关系的限制。具有两种或更多种不同孔径的混合芯已经被提出作为替代几何形状以增强毛细极限。在这项研究中，两个杂交方案的影响-在平面和平面外-对毛细管传输的混合芯进行了研究。来自面内混合芯的实验数据结合理论模型显示，液体-蒸汽弯月面曲率的局部变化（即，孔径）不会导致比可比的均匀吸液芯更高的质量流率。相反，液体-蒸汽弯月面的曲率的全局变化（如在平面外混合芯中发生的）对于获得大于均匀芯的质量流率是必要的。因此，在平面外的混合吸液芯的毛细极限和干涸的物理研究使用的混合吸液芯组成的1 μ m厚的高度多孔的网格悬浮在一个均匀的阵列的微柱。对结构内干燥过程的研究表明，补片的存在强烈改变了干燥机制。可视化研究表明，平面外的混合芯保持操作，只要液体被限制在网孔内;凹陷的弯月面下的网格的结果在瞬间局部干燥。为了保持网状结构内的液体，增加了网状厚度，并且确定网状厚度在平面外混合芯的性能中起着关键作用。
The mass transport capacity (i.e., the capillary limit,) of homogeneous wicks is limited by the inverse relation between the capillary pressure and permeability. Hybrid wicks with two or more distinct pore sizes have been proposed as alternative geometries to enhance the capillary limit. In this study, the impact of the two hybridization schemes-in-plane and out-of-plane-on the capillary transport of hybrid wicks is studied. Experimental data from in-plane hybrid wicks in conjunction with a theoretical model show that local changes in the curvature of the liquid-vapor meniscus (i.e., pore size) do not result in a higher mass flow rate than that of a comparable homogeneous wick. Instead, a global change in the curvature of the liquid-vapor meniscus (as occurring in out-of-plane hybrid wicks) is necessary for obtaining mass flow rates greater than that of a homogeneous wick. Therefore, the physics of capillary limit and dryout in out-of-plane hybrid wicks is investigated using a hybrid wick consisting of a 1-μm-thick highly porous mesh suspended over a homogeneous array of micropillars. A study of the dryout process within the structure revealed that the presence of the mesh strongly alters the dryout mechanism. Visualization studies showed that out-of-plane hybrid wicks remain operational only as long as the liquid is constrained within the mesh pores; recession of the meniscus just below the mesh results in instantaneous local dryout. To maintain liquid within the mesh structure, the mesh thickness was increased, and it was determined that the mesh thickness plays the key role in the performance of an out-of-plane hybrid wick.