Two-Dimensional Analysis of Air–Water Interface on Superhydrophobic Grooves under Fluctuating Water Pressure

Piao, Linfeng,Park, Hyungmin American Chemical Society 2015 Langmuir Vol.31 No.29

<P>We theoretically investigate the collapse (i.e., wetting) transition of the air Water interface on fully submerged superhydrophobic surfaces with micro-sized grooves under the fluctuating water pressure and the diffusion of the trapped air pockets. For the analysis, a nonlinear oscillator equation to describe the dynamics of the two-dimensional air water interface on a single groove is derived, which is solved for a range of parameters of groove geometry and harmonically fluctuating water pressure. The results show that the pressure fluctuation across the interface entourages the early collapse of a plastron before reaching the critical hydrostatic pressure (i.e., maximum immersion depth) predetermined by the geometry. The dependence of plastron longevity on the surface geometry is found such that the plastron on a narrow groove (<=similar to 5 mu m) (collapses mostly due to gas diffusion) lasts days while the ones on wider grooves (>similar to 35-45 mu m, for example), more susceptible to the oscillating pressure, last a much shorter duration. The interplay between the air compression due to water impalement and the change of the volume of impaled water due to gas diffusion determines the response of plastron to fluctuating water pressure, which is analyzed in detail through the introduction of nondimensional parameters, and the critical groove width (most vulnerable to the external perturbations) is explained further. Finally, as a countermeasure to the fluctuating water pressure, it is suggested that the enhanced advancing contact angle of the groove sidewall (e.g., hierarchical structure) Mitigates the negative effects.</P>

Effects of geometrical parameters of an oil-water separator on the oil-recovery rate

Linfeng Piao,김나영,박형민 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.6

As the economical and environmental damages due to the accidental oil-spills in marine environment increase gradually, more activecountermeasure needs to be developed. In this respect, in the present study, we propose a new design of oil-water separation system andinvestigate the effects of several geometrical features on the oil-recovery rate, based on a two-dimensional numerical simulation. Theworking mechanism of current separator is to utilize the density difference between the oil and water, which is strengthened by addingmomentum to the oil-water mixture flow through a “U-shaped” passage. Along the flow passage, we locate additional parts such as baffleplate, weir plate, and water outlet. While optimizing the conditions of these to maximize the oil recovery, it is found that the formationand stable retention of water layer between the water outlet and weir plate is critical to separate and store the above-layered oil. Finally,these findings are further confirmed with a basic experimental test with a three-dimensional oil-water separator model.

Relation between oil-water interfacial flow structure and their separation in the oil-water mixture flow in a curved channel: An experimental study

Piao, Linfeng,Park, Hyungmin Elsevier 2019 International journal of multiphase flow Vol.120 No.-

<P><B>Abstract</B></P> <P>We investigate the oil-water separation in a curved channel under a range of inflow conditions, focusing on the fundamental multiphase flow physics occurring at the oil-water interface. With a silicone oil (viscosity: 10 mm<SUP>2</SUP>/s, density: 935 kg/m<SUP>3</SUP>), we perform a series of water-tunnel experiments to measure the evolution of oil-water mixture flow inside a curved channel, devised for realizing a continuous and effective oil recovery (separation). The oil-water mixture velocity at the channel inlet is 1.35–2.35 m/s (Reynolds and Froude numbers based on the inlet height and length of the channel are 0.6–2.0 × 10<SUP>4</SUP> and 0.14, respectively), and we vary the inlet oil volume fraction as 0.49–0.85. We find that the efficiency of oil separation is strongly affected by the oil-water interfacial flow structures and identify two typical flow patterns: wavy oil-water interface and dispersed-oil flow. When the inlet oil fraction is high ( > 0.74), the instability occurring at the wavy oil-water interface plays a dominant role in determining the oil recovery rate (which is as high as 80% in general). As the inlet oil fraction becomes smaller ( < 0.7), on the other hand, the oil dispersion starts to appear vigorously, which interferes with the oil separation process and the recovery rate drops below 60% at the oil fraction smaller than 0.5. Through the quantitative analysis of the optically measured oil-water interface phenomena, we suggest theoretical models to predict the oil recovery rate as a function of the interfacial fluctuation of wavy oil-water interface and the fraction of dispersed oil phase, depending on the inlet flow conditions. We also propose a strategy to maximize the oil recovery rate of large-scale oil-water separation device, which is expected to be beneficial in many applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Continuous and large-scale separation and recovery of oil confirmed experimentally in a curved channel geometry: oil recovery rate over 80% is achieved at higher inlet oil fraction. </LI> <LI> Flow visualization of oil-water mixture flow in a channel: oil recovery performance shows a strong dependence on two interfacial flow phenomena inside the channel: wavy oil-water interface and dispersed oil flow. </LI> <LI> Quantification of the oil-phase by image processing: we introduced two dimensionless parameters related to specific flow patterns and proposed theoretical correlations to link them to the oil recovery rate. </LI> </UL> </P>

해양 기름유출사고 대응을 위한 유회수장비 내부 기름-물 혼합유동에 대한 분석

박임봉(Linfeng Piao),박형민(Hyungmin Park) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.4

압력섭동이 초소수성 표면 위의 공기-물 경계면에 미치는 영향에 대한 모델링 연구

박임봉(Linfeng Piao),박형민(Hyungmin Park) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

To transfer the recent success of turbulent drag reduction on superhydrophobic(SHPo) surfaces in laboratory environments to real applications, it is critical to evaluate the stability of the plastron under the fluctuating turbulent condition of wetting transition on a SHPo surface made up of longitudinal microgrates under the fluctuating pressure. Assuming the sinusoidal variation of the hydrodynamic pressure above the surface, we derive the energy balance which leads to the oscillator equation to predict the unsteady behavior of the plastron interface while explaining the collapse of the plastron interface depending on the fluctuating pressure when the contact lines remain pinned at the edges. The present modeling is expected to provide valuable information(in terms of critical pressure and natural frequency) for devising the robust SHPo surfaces for applications in turbulent flows.

저유황유 점도변화 및 수면 위 확산 특성 분석

이재빈(Jaebeen Lee),박임봉(Linfeng Piao),박형민(Hyungmin Park) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

This study investigated the viscosity of low sulfur fuel oil (LSFO) using bench-scale experiments and analyzed the effects of emulsion and evaporation on it. The results show the dependency of LSFO on the temperature, which follows the William-Landel-Ferry law. The emulsion test found that the meso-stable emulsion whose viscosity is 10-100 times larger than the normal one was achieved. Evaporation of LSFO due to initial temperature is found to be so small that its effect on oil properties is negligible in the present study. In addition, we experimentally examined the spreading features of LSFO on the water surface in the circulating water bath in which the wind speed, water temperature, and initial oil volume are controlled as 2-5 m/s, 5-25 ℃, and 100-400 ml, respectively. The spreading speed rapidly increased after a critical viscosity (~500 cP) due to the balance break between the viscosity retarding force and wind shear stress.

저유황유 점도변화 및 수면 위 확산 특성 분석

이재빈(Jaebeen Lee),박임봉(Linfeng Piao),박형민(Hyungmin Park) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

This study investigated the viscosity of low sulfur fuel oil (LSFO) using bench-scale experiments and analyzed the effects of emulsion and evaporation on it. The results show the dependency of LSFO on the temperature, which follows the William-Landel-Ferry law. The emulsion test found that the meso-stable emulsion whose viscosity is 10-100 times larger than the normal one was achieved. Evaporation of LSFO due to initial temperature is found to be so small that its effect on oil properties is negligible in the present study. In addition, we experimentally examined the spreading features of LSFO on the water surface in the circulating water bath in which the wind speed, water temperature, and initial oil volume are controlled as 2-5 m/s, 5-25 ℃, and 100-400 ml, respectively. The spreading speed rapidly increased after a critical viscosity (~500 cP) due to the balance break between the viscosity retarding force and wind shear stress.

전단율 및 온도에 따른 저유황유 확산 특성 분석

이재빈(Jaebeen Lee),박임봉(Linfeng Piao),박형민(Hyungmin Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

The rheological behavior of LSFO (low sulfur fuel oil) has been issued after the IMO (International Maritime Organization) restricted the sulfur percentage of marine oil as below as 0.5%. Therefore, to cope with the oil-spill accident in the marine environment, the characteristics of LSFO should be known to establish the strategy dealing with preventing the dispersion of LSFO and removing them. In this paper, based on the viscosity of LSFO (available from the domestic companies) at the temperature range of 4-50℃, its dispersion characteristics were analyzed in the water flume experiment, by varying the shear rate, i.e., wind speed over the water surface. The viscosity was modeled as function of temperature using WLF law and transition temperature of LSFO was found. The actual marine oil-spill condition was mimicked with the wind speed of 3-7 m/s, 5-25℃ of water temperature, with the added volume of oil of 100-200 ml. In addition to the variation of viscosity with temperature, we measured the pattern of oil dispersion over the water surface, which was processed to obtain the dispersion coefficient as a function of shear rate and viscosity (i.e., temperature) of LSFO.

Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system

Kang, Daeshik,Pikhitsa, Peter V.,Choi, Yong Whan,Lee, Chanseok,Shin, Sung Soo,Piao, Linfeng,Park, Byeonghak,Suh, Kahp-Yang,Kim, Tae-il,Choi, Mansoo Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.516 No.7530

Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider’s slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0–2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection–reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.