Evaporative Drying from Hydrophilic or Hydrophobic Homogeneous Porous Columns: Consequences of Wettability, Porous Structure and Hydraulic Connectivity
Evaporative Drying from Hydrophilic or Hydrophobic Homogeneous Porous Columns: Consequences of Wettability, Porous Structure and Hydraulic Connectivity
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DOI：
10.1007/s11242-022-01775-7
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发表时间：
2022-04
影响因子：
2.7
通讯作者：
P. Chakraborty;M. Ross;H. Bindra;M. Derby
中科院分区：
文献类型：
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作者：
P. Chakraborty;M. Ross;H. Bindra;M. Derby
多孔介质的蒸发干燥受润湿性和多孔结构的影响;改变这些参数会影响毛细管效应和水力连通性，从而实现更慢或更快的蒸发。在本研究中，从用~ 1165玻璃（即，亲水的）或特氟隆（即，疏水）2.38 mm直径的球体，通过太阳模拟器提供1000 W/m2的热通量;每个实验重复五次，持续7天。本研究探讨了改变润湿性的蒸发与施加的热通量驱动蒸发的组合，同时部署X射线成像来测量蒸发锋。初始蒸发速率更快（即， ~ 1.5倍）。传统上将多孔介质中的蒸发分为三个阶段：恒定速率阶段、随后的下降速率阶段和速率较慢的阶段。由于均匀的多孔结构和相似的特征孔径（即，0.453 mm），毛细效应有限，导致蒸发速率恒定期不显著。蒸发率的急剧下降（即，下降速率期），其次是缓慢速率期的特点菲克扩散定律。与玻璃中的90小时相比，特氟龙样品在70小时后进入较慢的速率期，并且结合X射线可视化，这意味着特氟龙样品中的液体岛形成速率低于玻璃样品。通过X射线观察到的蒸发干燥前沿在玻璃中传播得更快，最终深度（7天后）为~ 30 mm，而在Teflon中为~ 24 mm。渗透率基于几何形状建模[例如，3.163 E −9 m2（Revil、格洛弗、Pezard和Zamora模型），3.287 E −9 m2（关键路径分析）]，并对玻璃（9.5 E−10 m2）和特氟龙（8.9 E−10 m2）样品进行了实验测量。计算了瑞利数（Ra= 2380）和努塞尔数（Nu= 4.1），用于量化水从完全饱和多孔介质中的自然蒸发，并计算了邦德数（Bo= 193 E−3）和毛细管数（Ca= 6.203 E−8），并与以前的研究进行了比较。
Evaporative drying from porous media is influenced by wettability and porous structures; altering these parameters impacts capillary effects and hydraulic connectivity, thereby achieving slower or faster evaporation. In this study, water was evaporated from a homogeneous porous column created with ~ 1165 glass (i.e., hydrophilic) or Teflon (i.e., hydrophobic) 2.38-mm-diameter spheres with an applied heat flux of 1000 W/m2supplied via a solar simulator; each experiment was replicated five times and lasted 7 days. This study investigates the combination of altered wettability on evaporation with an imposed heat flux to drive evaporation, while deploying X-ray imaging to measure evaporation fronts. Initial evaporation rates were faster (i.e., ~ 1.5 times) in glass than in Teflon. Traditionally, evaporation from porous media is categorized into three periods: constant rate, subsequent falling rate and slower rate period. Due to homogeneous porous structure and similar characteristic pore size (i.e., 0.453 mm), capillary effects were limited, resulting in an insignificant constant evaporation rate period. A sharp decrease in evaporation rate (i.e., falling rate period) was observed, followed by the slower rate period characterized by Fick’s law of diffusion. Teflon samples entered the slower rate period after 70 h compared to 90 h in glass, and combined with X-ray visualization, implying a lower rate of liquid island formation in the Teflon samples than the glass samples. The evaporative drying front, visualized by X-rays, propagated faster in glass with a final depth (after 7 days) of ~ 30 mm, compared to ~ 24 mm in Teflon. Permeability was modeled based on the geometry [e.g., 3.163E−9 m2(Revil, Glover, Pezard, and Zamora model), 3.287E−9 m2(Critical Path Analysis)] and experimentally measured for both glass (9.5 E−10 m2) and Teflon (8.9 E−10 m2) samples. Rayleigh numbers (Ra= 2380) and Nusselt (Nu= 4.1) numbers were calculated for quantifying natural evaporation of water from fully saturated porous media, and Bond (Bo= 193 E−3) and Capillary (Ca= 6.203 E−8) numbers were calculated and compared with previous studies.