Capillary pressure at irregularly shaped pore throats: Implications for water retention characteristics

Suh, Hyoung Suk,Kang, Dong Hun,Jang, Jaewon,Kim, Kwang Yeom,Yun, Tae Sup Elsevier 2017 ADVANCES IN WATER RESOURCES Vol.110 No.-

<P><B>Abstract</B></P> <P>The random shapes of pore throats in geomaterials hinder accurate estimation of capillary pressure, and conventional pore network models that simply use the Young–Laplace equation assuming circular pore throats overestimate the capillary pressure. As a solution to this problem that does not complicate the pore network model or slow its implementation, we propose a new morphological analysis method to correlate the capillary pressure at an irregular pore channel with its cross-sectional geometry using lattice Boltzmann (LB) simulation and Mayer and Stowe–Princen theory. Geometry-based shape factors for pore throats are shown here to correlate strongly with the capillary pressure obtained by LB simulation. Water retention curves obtained by incorporating the morphological calibration into conventional pore network simulation and their correlative scheme agree well with experimental data. The suggested method is relevant to pore-scale processes such as geological CO<SUB>2</SUB> sequestration, methane bubbling from wetlands, and enhanced carbon recovery.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Lattice Boltzmann simulation can accurately compute capillary pressure in irregular pore channels. </LI> <LI> Our morphological analysis estimates the effective pore throat shape to compute capillary pressure without lattice Boltzmann simulation. </LI> <LI> Pore network models calibrated by these specific capillary pressures produce water retention curves similar to experiment. </LI> </UL> </P>

수지이동 성형공정에서 기공형성에 미치는 모세관압의 영향에 관한 실험적 연구

이종훈,김세훈,김성우,이기준 한국유변학회 1998 Korea-Australia rheology journal Vol.10 No.4

수지이동 성형공정에서 섬유직조가 수지에 의해 함침될 때 발생하는 기공 또는 나쁜 젖음성은 최종 성형품의 물성 저하에 심각한 영향을 미치게 된다. 본 연구에서는 함침공정에서의 수지 유동특성을 파악하고 기공 형성기구를 규명하기 위하여, 빔 형태의 금형을 대상으로 실리콘 오일과 평직형태의 유리섬유를 사용하여 미시적인 유동가시화 실험을 수행하였다. 시간과 압력에 따른 수지의 침투길이를 측정함으로써 섬유직조의 기공률에 따른 비정상상태의 투과계수와 모세관압을 측정하였고, 낮은 조업압력과 낮은 기공률에서는 모세관압이 함침공정에서 중요한 가공변수임을 확인할 수 있었다. 비디오 카메라를 이용하여 유동전단면의 이동을 근접 확대 촬영하여 기공이 형성되는 과정을 미시적으로 관찰함으로써, 섬유와 수지의 표면에너지에 의해 발생되는 모세관압이 기공의 형성에 미치는 영향을 조사하였다. 그 결과, 수지충전을 유발하는 전체 구동압력에서 모세관압이 상대적으로 클수록 기공은 더욱 쉽게 생성되는 것으로 나타났다. 또한 수지의 점도와 섬유직조의 기공률이 각각 변화할 때, 모세관수에 따른 기공의 함량을 화상 해석 기법(image analysis technique)을 사용하여 정량적으로 측정하였다. 수지가 섬유직조 내로 함침될 때 임계모세관수(Ca~2.75$\times$$10^{-3})이상에서는 기공이 형성되지 않았으며, 그 이하에서는 모세관수가 감소함에 따라 기공의 함량이 지수적으로 증가하였다. 생성된 기공의 함량은 점도에 관계없이 유사한 변화 경향을 보였으며, 모세관수가 동일한 조건에서는, 기공률이 감소함에 따라 기공의 함량이 감소하였다. Flow-induced voids during resin impregnation and poor fiber wetting give serious effects on the mechanical properties of composites in resin transfer molding process. In order to better understand the characteristics of resin flow and to investigate the mechanism of void formation, flow visualization experiment for the resin impregnation was carried out on plain weaving glass fiber mats using silicon oils with various viscosity values. The permeability and the capillary pressure for the fiber mats of different porosities were obtained by measuring the penetration length of the resin with time and with various injection pressure. At low porosity and low operating pressure, the capillary pressure played a significant role in impregnation process. Video-assisted microscopy was used in taking the magnified photograph of the flow front of the resin to investigate the effect of the capillary pressure on the void formation. The results showed that the voids were formed easily when the capillary pressure was relatively high. No voids were detected above the critical capillary number of 2.75$\times$$10^{-3}, and below the critical number the void content increased exponentially with decrease of the capillary number. The content of void formed was independent of the viscosity of the resin. For a given capillary number, the void content reduced with the lower porosity of the fiber mat.

당뇨병성 신장병증을 가진 환자에서 급성 진피 내 모세혈관 파열

유혜민 ( Hea Min Yu ),윤해은 ( Hae Eun Yun ),백영하 ( Young Ha Baek ),전형구 ( Hyung Ku Chon ),박경택 ( Kyung Taek Park ),안대선 ( Dae Seon Ahn ),강경표 ( Kyung Pyo Kang ),김원 ( Won Kim ),박성광 ( Sung Kwang Park ),이식 ( Sik L 대한신장학회 2010 Kidney Research and Clinical Practice Vol.29 No.4

A 46-year-old diabetic woman visited our hospital with generalized edema and high blood pressure. An appropriately sized noninvasive blood pressure cuff was placed on her right arm above the elbow to measure blood pressure. While we were checking her blood pressure, we noticed small red petechial spots distal to the cuff involving her entire right forearm. Her blood pressure was 170/96 mmHg. The laboratory findings showed no abnormality of anticoagulation. The rest of the patient`s extremities were not affected. The petechiae on the right arm resolved spontaneously after ten days. The most likely explanation for these petechiae is acute dermal capillaryrupture, which is called the Rumpel-Leede phenomenon. Acute dermal capillary rupture appears as petechiae in an area following application of vascular constriction such as application of tourniquet to draw blood specimen or use of blood pressure cuff due to capillary fragility or abnormal platelets in numbers or in function. This situation has been reported previously in the literature as the Rumpel-Leede phenomenon in association with prolonged noninvasive BP monitoring. In the patient described herein, increased venous pressure from blood pressure measurement and capillary fragility associated with diabetes mellitus may have increased the risk of acute dermal capillary rupture.

Capillary rheometry of polymer melts - Simulation and experiment

Seppo Syrjala,Johanna Aho 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.3

This paper discusses shear viscosity measurements of polymer melts by the capillary rheometer. Particular emphasis is placed on investigating the effects of viscous heating and pressure dependence of viscosity in capillary flows. The capillary flow problem is addressed by means of numerical simulation using the finite element method to solve the equations of continuity, momentum and energy along with the viscosity model that accounts for the dependence on shear rate, temperature and pressure. Simulations clearly reveal that vis\-cous heating and pressure dependence of viscosity can have a considerable impact on capillary rheometer experiments. On the other hand, as far as the pressure drop over the capillary is concerned, it is possible that these two contributing factors compensate for each other. Selected experimental data from the capillary rheometer are also presented and discussed in connection with the simulated results.

Capillary rheometry of polymer melts - Simulation and experiment

Syrjala, Seppo,Aho, Johanna 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.3

This paper discusses shear viscosity measurements of polymer melts by the capillary rheometer. Particular emphasis is placed on investigating the effects of viscous heating and pressure dependence of viscosity in capillary flows. The capillary flow problem is addressed by means of numerical simulation using the finite element method to solve the equations of continuity, momentum and energy along with the viscosity model that accounts for the dependence on shear rate, temperature and pressure. Simulations clearly reveal that viscous heating and pressure dependence of viscosity can have a considerable impact on capillary rheometer experiments. On the other hand, as far as the pressure drop over the capillary is concerned, it is possible that these two contributing factors compensate for each other. Selected experimental data from the capillary rheometer are also presented and discussed in connection with the simulated results.

A stand-alone pressure-driven 3D microfluidic chemical sensing analytic device

Shin, Jae-Ho,Lee, Gi-Ja,Kim, Wansun,Choi, Samjin Elsevier 2016 Sensors and actuators. B, Chemical Vol.230 No.-

<P><B>Abstract</B></P> <P>This study introduces a new stand-alone pressure-driven 3D microfluidic chemical sensing analytic device (PD-PAD), fabricated by enclosing a cover substrate and inserting a void-channeled substrate on a conventional capillary-driven microfluidic paper-based analytical device (CD-PAD). Adhesive cold-laminating film and filter paper were used as a substrate. The flow rates of 3D PD- and CD-PAD platforms were compared through five different character-shaped microfluidic channels. A single 60-μL drop of fluid inducing 0.4mbar of pressure showed that the PD-PAD was roughly 300-fold faster than the CD-PAD. The more input pressure in the PD-PAD increased, the more flow increased. The structures with the curved channels less than 90° led to a decreased flow rate in the CD-PAD, but did not affect the PD-PAD. The superior flow rate in the PD-PAD was likely due to the concurrence of the pressure-driven and capillary-driven flows. The glucose and albumin concentrations with a clinically relevant range and pH levels were successfully detected. Therefore, a stand-alone 3D microfluidic PD-PAD platform has great potential for assessing for the presence of diseases in very urgent situations such as the operating room or for use in low-cost and fast point-of-care applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The pressure-driven flow (PD-PAD) was roughly 300-fold faster than the capillary-driven flow (CD-PAD). </LI> <LI> The more the input pressure increased, the more the flow increased. </LI> <LI> The curved channels less than 90° led to a decreased flow rate in the CD-PAD, but did not affect the PD-PAD. </LI> <LI> The superior flow rate in the PD-PAD was likely due to the concurrence of the pressure- and capillary-driven flows. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Investigation of the Gas Breakthrough Pressure of Cement Mortar with Different Experimental Techniques

Zirui Cheng,Bin Ye,Jihui Zhao 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.1

The gas breakthrough property of cement-based material is an important indicator with which to evaluate the sealing efficiency. Gas breakthrough experiments can be used to obtain the gas breakthrough pressure. However, different techniques for measuring the gas breakthrough pressure usually yield different results. In this paper, three commonly used experimental methods, including the step-by-step approach, the residual capillary pressure approach, and the mercury intrusion porosimetry (MIP) approach, are adopted to investigate the gas breakthrough pressure of mortar samples. The results of the three approaches are analyzed from the perspective of the definition of gas breakthrough, and it shows that the gas breakthrough pressures measured by the step-by-step approach are the most representative values. The MIP approach underestimates the breakthrough pressure due to the lack of confining pressure, and the residual capillary pressure approach represents the gas migration and water reimbibition process after the gas breakthrough. Theoretical analysis and fitting of experimental results show that the gas breakthrough pressure is linear with the permeability on a log-log coordinate.

사각 공동 및 채널이 형성된 마이크로 구조 표면에서의 수조비등 특성연구

김동억(Dong Eok Kim),박수청(Su Cheong Park),유동인(Dong In Yu),김무환(Moo Hwan Kim),안호선(Ho Seon Ahn),명병수(Byung-Soo Myung) 대한기계학회 2016 大韓機械學會論文集B Vol.40 No.6

사각공동 및 채널이 형성된 마이크로구조 표면을 활용하여 수조비등 임계열유속에 대한 중력 및 모세관 압력의 영향에 대해 연구하였다. 마이크로 공동구조는 모세관 압력에 의한 액체유동을 억제하는 역할을 하였고, 마이크로 채널구조는 비등표면으로의 1차원적인 액체유동을 유발하는데 기여하였다. 이를통해 임계열유속과 모세관 유동의 상관관계를 정량화할 수 있었다. 비등표면으로의 액체공급을 위한 원동력은 중력수두 및 모세관 압력에 의해 유발될 수 있다. 본 연구에서는 수조비등 실험 및 가시화 데이터의 분석을 통해 수조비등 표면에서의 핵비등을 유지할 수 있는 액체공급은 중력 수두 및 모세관 압력과 밀접한 상관관계를 가지고 있음을 확인할 수 있었다. Based on a surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool-boiling Critical Heat Flux (CHF). The microcavity structures could prevent liquid flow by the capillary pressure effect. In addition, the microchannel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow was clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through an analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related to the gravitational pressure head and capillary pressure effect.

사각 공동 및 채널이 형성된 마이크로 구조 표면에서의 수조비등 특성연구

김동억(Dong Eok Kim),박수청(Su Cheong Park),유동인(Dong In Yu),김무환(Moo Hwan Kim),안호선(Ho Seon Ahn),명병수(Byung-Soo Myung) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Based on the surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool boiling Critical Heat Flux (CHF). The micro-cavity structures could prevent the liquid flow by capillary pressure effect. And, the micro-channel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow had been clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through the analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related with the gravitational pressure head and capillary pressure effect.

Modifying capillary pressure and boiling regime of micro-porous wicks textured with graphene oxide

Jo, Hong Seok,An, Seongpil,Nguyen, Xuan Hung,Kim, Yong Il,Bang, Boo-Hyoung,James, Scott C.,Choi, Jeehoon,Yoon, Sam S. Elsevier 2018 Applied thermal engineering Vol.128 No.-

<P><B>Abstract</B></P> <P>Liquid flow inside a heat pipe due to capillary forces can be used to cool electronic devices. To promote capillary-driven flow, a multilayer, porous wicking surface was designed for optimal liquid transport. The multilayer-porous structure consists of micro-porous structure decorated with nanomaterials. Herein, we demonstrate that micro-porous copper coated with graphene oxide (GO) has elevated capillary forces that can increase both the critical heat flux and the convective heat transfer coefficient. The thin GO layer promotes hydrophilicity that enhances the wettability of the wicking surface. However, an excessively thick GO coating can decrease permeability even in the presence of increased capillary pressures such that overall flow is hindered. In this work an optimal coating thickness is identified and characterized by heat-transfer experiments and scanning electron microscopy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A highly porous wicking surface was introduced to promote capillary-driven flow in a heat pipe. </LI> <LI> Micro-porous copper coated with graphite oxide (GO) increased the critical heat flux. </LI> <LI> The thin GO layer promotes hydrophilicity that enhances the wettability of the wicking surface. </LI> <LI> Narrowed pores due to the GO layer increase the capillary pressure and the wicking effects. </LI> </UL> </P>