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Статті в журналах з теми "Washburn's equation":

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Labajos-Broncano, L., M. L. González-Martı&#x;n, and J. M. Bruque. "Washburn's Equation Facing Galileo's Transformation: Some Remarks." Journal of Colloid and Interface Science 253, no. 2 (September 2002): 472–74. http://dx.doi.org/10.1006/jcis.2002.8521.

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2

Chibowski, Emil, and Lucyna Hołysz. "On the use of Washburn's equation for contact angle determination." Journal of Adhesion Science and Technology 11, no. 10 (January 1997): 1289–301. http://dx.doi.org/10.1163/156856197x00147.

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3

Ramesh, Babu V., G. Ramakrishnan, V. S. Subramanian, and Lakshmi Kantha. "Analysis of Fabrics Structure on the Character of Wicking." Journal of Engineered Fibers and Fabrics 7, no. 3 (September 2012): 155892501200700. http://dx.doi.org/10.1177/155892501200700305.

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In this article, the effect of weave pattern on fabric wicking was analyzed. Weaves are distributed into two groups, i.e. weaves, the floats of which are distributed in even intervals throughout the entire surface of fabric, and horizontally striped weaves. The wickability properties of all tested fabrics are determined using a newly developed electronic vertical wicking tester. It was determined that the results of wicking horizontally striped fabrics were higher than those of weaves with evenly distributed floats. Washburn's equation obeyed quite well when the time constant is near 0.5. In fact, the time constant for plain and fancy twill weave were exponentially lower than those of other fabrics. This can be considered a measure of fabric rigidity.
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Labajos-Broncano, L., M. L. González-Martín, J. M. Bruque, and C. M. González-García. "Comparison of the Use of Washburn's Equation in the Distance–Time and Weight–Time Imbibition Techniques." Journal of Colloid and Interface Science 233, no. 2 (January 2001): 356–60. http://dx.doi.org/10.1006/jcis.2000.7283.

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Labajos-Broncano, L., M. L. González-Martı́n, J. M. Bruque, C. M. González-Garcı́a, and B. Jańczuk. "On the Use of Washburn's Equation in the Analysis of Weight–Time Measurements Obtained from Imbibition Experiments." Journal of Colloid and Interface Science 219, no. 2 (November 1999): 275–81. http://dx.doi.org/10.1006/jcis.1999.6492.

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6

Ji, Lingyun, and Baoli Shi. "A novel method for determining surface free energy of powders using Washburn's equation without calculating capillary factor and contact angle." Powder Technology 271 (February 2015): 88–92. http://dx.doi.org/10.1016/j.powtec.2014.11.002.

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Alsamia, Shaymaa, Mohammed Sh Mahmood, and Ali Akhtarpour. "Estimation of capillary rise in unsaturated gypseous sand soils." Pollack Periodica 15, no. 2 (August 2020): 118–29. http://dx.doi.org/10.1556/606.2020.15.2.11.

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AbstractThe phenomenon of capillary rise happens in soils, and it has a crucial effect on many engineering applications. Many researchers have concluded several experimental equations to estimate this height. This paper presents a comparative and practical study of the three most important equations used in most researches, which are Lane and Washburn, Fetter, and P-K equations. The estimated heights by these three equations were compared with the experimental tests on sand samples taken from Al-Adalah, Al-Furat, and Al-Jameah districts located in Al-Najaf city in the southwest of Iraq. The percentage change for each equation compared with the experimental work. The results illustrated that the Fetter equation is the closest equation to experimental height and gives moderate values, unlike the Lane and Washburn and P-K equations, to save estimation of the pollutants penetration in unsaturated soils.
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DASARATHAN, KAMALRAJ, and SUBRAMANIAM VENKATRAMAN. "Validity of Washburn’s equation in sericin treated polyester fabric." Industria Textila 70, no. 01 (March 2019): 94–97. http://dx.doi.org/10.35530/it.070.01.1537.

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Application of sericin to polyester and cotton fabrics will bring about a number of advantages in that the materials become hydrophilic and are capable of imparting antimicrobial effect. Also, the materials can be dyed using reactive dyes. A considerable amount of work has been carried out on the application of sericin to polyester and cotton fabrics. Wickability of treated fabrics has been studied and it was demonstrated that there was an improvement. A detailed analysis of study is warranted on wickability as the work done on it was scant. It is necessary to validate Washburn’s equation which constitutes an important component of kinetics of wicking in this paper. The validity of Washburn’s equation for a set of data on wickability of sericin treated polyester fabrics is studied. Untreated polyester fabric and treated with caustic soda and plasma followed by sericin treatment using DMDHEU and Glutaraldehyde were taken for wicking studies. Two models were used. From the slopes it is found that Washburn’s equation is followed.
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SĘK, Jerzy, Olga S. SHTYKA, and Kamila SZYMCZAK. "MODELING OF THE SPONTANEOUS POLYPROPYLENE SORBENTS IMBIBITION WITH EMULSIONS." JOURNAL OF ENVIRONMENTAL ENGINEERING AND LANDSCAPE MANAGEMENT 23, no. 2 (December 2014): 83–93. http://dx.doi.org/10.3846/16486897.2014.961926.

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Oil penetration into aqueous media results in various chemical and physical processes including formation of “oil-in-water” emulsions, that have devastating effects on the environment. This research was conducted to evaluate the kinetics of permeation of “oil-in-water” emulsions into synthetic porous material. It gives the ability to develop more effective sorbents, decreasing risks of negative consequences and environmental contamination. The following publication focuses on assessment of the possibility to describe and predict a process of porous medium imbibition with emulsions by means of the Hill equation. Its adequacy is compared with the classical Lucas–Washburn equation and its modified version. The advanced approach is to substitute the commonly used parameter of the height of an imbibed emulsion (h(t)) by the parameter mh(t), which is the mass of an imbibed emulsion in the case of the classical and modified Washburn equations. According to the obtained results, the Hill equation provides the most appropriate and precise description of the porous material imbibition with “oil-in-water” emulsions and oil in comparison with others, and shows the highest correlation values (Rav = 0.995±0.001) and the lowest normalized root mean square error (NRMSEav 1.95±0.138).
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Villagrán Zaccardi, Yury, Natalia Alderete, and Nele De Belie. "Lucas-Washburn vs Richards equation for the modelling of water absorption in cementitious materials." MATEC Web of Conferences 199 (2018): 02019. http://dx.doi.org/10.1051/matecconf/201819902019.

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The Lucas-Washburn equation is still being applied by a significant number of researchers for the modelling of water absorption in cementitious materials. A modern approach considers the extended Darcy’s law leading to the Richards equation instead. Three main assumptions are implied by the application of the Lucas-Washburn equation: the flow occurs in one direction only, the material is separated into one fully wet and one fully dry region, and pores are modelled as an assembly of parallel tubes of a particular radius. Its application to analyse experimental results allows defining these three assumptions as mere simplifications. Therefore, all the parameters comprised in the Lucas-Washburn model are apparent. Consequently, a very limited description of the transport properties of the material can be achieved. For many engineering purposes this would not be an issue, but for an intrinsic description of the material a more realistic model is required. This paper discusses the limitations of the Lucas-Washburn equation, and the advantages of the Richards equation regarding the modelling of water absorption in cementitious materials. The comparative analysis reveals the versatility of the Richards equation, with an approach that considers the material as a continuum and describes it through measurable parameters.

Дисертації з теми "Washburn's equation":

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Gagnon, Yancie. "Étude de l’extraction des huiles végétales en milieu aqueux assistée par des tensioactifs." Electronic Thesis or Diss., Compiègne, 2021. http://www.theses.fr/2021COMP2654.

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L’une des préoccupations actuelles majeures des acteurs de la trituration repose sur l’identification d’une alternative au procédé utilisant l’hexane en raison de son impact sur l’environnement, la qualité des produits et la santé humaine. L’utilisation de l’eau comme solvant de substitution présente plusieurs avantages, mais cette piste a été longtemps écartée en raison de la non miscibilité de l’eau et des huiles. La solution proposée suggère d’utiliser une solution aqueuse de tensioactifs permettant la réduction de la tension interfaciale entre l’eau et l’huile sous les 10-2 mN/m (i.e. la formation de microémulsion). Cette thèse vise donc à étudier l’extraction des huiles végétales à partir de graines oléagineuses en milieux aqueux en présence de tensioactifs. L’objectif principal est d’acquérir une meilleure compréhension des mécanismes mis en jeu et notamment des interactions physicochimiques entre les différents composés du système. Différentes questions ont été abordées dans cette thèse de façon à prendre en considération pas à pas le rôle et l’impact de chaque constituant du système. D’abord, la caractérisation physicochimique de différents types de tensioactifs, en particulier les tensioactifs dits rallongés et les tensioactifs biosourcés largement moins étudiés dans la littérature, a permis de sélectionner ceux capables de solubiliser un maximum d’huile végétale dans l’eau. Ensuite, les systèmes étudiés se complexifient par la prise en compte des graines oléagineuses, et donc de l’interface solide-liquide jamais étudiée dans la littérature. Des hypothèses quant aux mécanismes d’action des tensioactifs sur la modification de la mouillabilité des surfaces oléagineuses ont pu être proposées. Finalement, l’étude du procédé d’extraction a été abordée. L’influence des paramètres opératoires sur les rendements d’extraction a été appréhendée. Les résultats obtenus offrent des perspectives de poursuite, dans le but d’envisager l’émergence de cette technologie à l’échelle industrielle
One of the major current concerns in the crushing industry is to identify an alternative to the processthat uses hexane because of its impact on the environment, product quality, and human health. Theuse of water as a substitute solvent has several advantages, but this path has long been set apart dueto the immiscibility of water and oils. The proposed solution suggests using an aqueous solution ofsurfactants allowing the reduction of the interfacial tension between water and oil below 10-2 mN/m(i.e., the formation of microemulsion). This thesis, therefore, aims to study the extraction of vegetable oils from oilseeds in aqueous media in the presence of surfactants. The main objective is to acquire a better understanding of the mechanisms involved, in particular, the physicochemical interactions between the different compounds of the system. Different questions have been addressed in this thesis to consider step by step the role and the impact of each constituent of the system. First, the physicochemical characterization of different types of surfactants, in particular, the so-called extended surfactants and bio-based surfactants that are largely less studied in the literature, which made it possible to select those capable of solubilizing a maximum of vegetable oil in water. Then, the studied systems become more complex by considering the oilseeds, therefore the solid-liquid interface, which has never been studied inthe literature. Hypotheses as to the mechanisms of action of surfactants on the wettabilitymodification of oleaginous surfaces have been proposed. Finally, the study of the extractionprocess was approached. The influence of the operating parameters on the extraction yields hasbeen apprehended. The results obtained offer prospects for further action to consider the emergenceof this technology on an industrial scale
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Kulkarni, Prashant S. "Mixed Hydrophilic/Hydrophobic Fiber Media for Liquid-Liquid Coalescence." Text, University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1310686055.

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Stables, Christa Lauren. "Wetting and Penetration Behavior of Resin/Wood Interfaces." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/79700.

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The goal of this project was improve the fundamental understanding of the wood-resin interaction, by looking at the relationship between the resin wetting onto wood and the resulting penetration into wood lumens. Wetting was analyzed with the sessile drop method, which observed the initial contact angle and change in contact angle over 35s. Penetration was measured within each individual tracheid. The Lucas-Washburn equation analyzed the wetting and penetration by calculating the penetration and comparing it to the measured penetration. Wetting of four resins was compared on 3 species, to improve the understanding of adhesive wetting behavior. This study agreed with previous research, that the non-aqueous resin exhibited favorable wetting and presumably better penetration than aqueous resins, with exception of urea-formaldehyde. Wetting and penetration of pMDI was studied on 5 wood species using the Lucas-Washburn equation. The wetting behaviors exhibited grain and species effects, which had implications on the resin availability for flake/strand-based composite products. The greater surface energy of loblolly pine most likely accounted for the significantly greater penetration of loblolly pine compared to Douglas-fir. The calculated penetration, via the Lucas-Washburn equation, exceeded the measured penetration, but it was concluded that the Lucas-Washburn equation predicted penetration reasonably well. Wetting and penetration of phenol-formaldehyde and subsequent adhesives was compared on 3 wood species using the Lucas-Washburn equation. All contact angles were unfavorable due to a skin formation. The Lucas-Washburn equation did not predict any penetration; however, penetration was observed with all systems. The findings suggest that the system was too complex for the Lucas-Washburn equation to be able to predict accurately.
Master of Science

Частини книг з теми "Washburn's equation":

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"Wettability of porous materials, II: Can we obtain the contact angle from the Washburn equation?" In Contact Angle, Wettability and Adhesion, Volume 4, 155–76. CRC Press, 2006. http://dx.doi.org/10.1201/b12166-11.

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Тези доповідей конференцій з теми "Washburn's equation":

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Chen, Tailian. "Capillary Force-Driven Fluid Flow of a Wetting Liquid on a Surface With Multiple Parallel Open Microchannels." In ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icnmm2012-73113.

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Fluid flow driven by the capillary force is omnipresent in nature and important in many engineering technologies. The focus of this work is capillary force-driven fluid flow of a wetting liquid in open microchannels when a liquid droplet is gently introduced to a metal surface on which multiple parallel microchannels with an open rectangular cross section are formed. It is found that, aided with a high-speed camera, the capillary-force driven fluid behavior consists of uni-directional spreading of the bulk droplet on the microchannel fins and liquid penetration into the microchannels. The kinetics of fluid flow due to the liquid penetration into the microchannels can be divided into three distinct stages: initial stage, transition stage, and Washburn stage; only in the Washburn stage, the flow has a penetration length-time dependence in proportion to square root of time as described by the Washburn’s equation. Comparison with liquid spreading on a plain surface having only one microchannel (the same geometry and size) revealed that the bulk droplet spreading on the microchannel fins, after elapse of the initial stage, has little effect on the fluid flow kinetics in the multiple microchannels. Some analytical results shed more insights into the capillary force-driven fluid flow in open microchannels.
2

Moeini Sedeh, Mahmoud, and J. M. Khodadadi. "Experimental Investigation of Wicking Flow Through a Porous Medium as a Validation Approach for Numerical Simulations." In ASME 2013 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/fedsm2013-16466.

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Wicking flow through a porous medium with nearly-spherical interconnected pores was investigated experimentally for validation of numerical simulations of multiphase flow through a porous structure. The experimental setup was designed to eliminate the effects of pressure gradient and gravity. The porous structure is a commercial graphite foam (PocoFoam® with an average pore size of 400 μm and porosity of 75%) and the penetrating liquid is cyclohexane. The penetration of the liquid into the foam sample is unidirectional. The liquid originates from a side reservoir toward an empty reservoir on the opposite side, with the porous sample between the reservoirs. The level of the liquid was kept constant on the fluid source side of the sample, i.e. in the reservoir full of liquid. Since the top side of the experimental setup is exposed to the ambient, there is no pressure gradient effect. Thus, penetration of the liquid occurs only as a result of interfacial effects (i.e. surface tension and contact angle) while pressure gradient and gravity play negligible roles. The instantaneous liquid penetration length (i.e. the average position of liquid interface) versus time was measured experimentally using video frame analysis of the tests recorded with a digital camera aligned with the experimental setup and observing from the top. The experiments were repeated several times to ensure their repeatability and the variations of the liquid interface position were obtained at different time instants. The results exhibit agreement with the theoretical Washburn equation for the liquid penetration length for horizontal wicking along cylindrical capillaries. Moreover, the possible causes of deviations from the Washburn equation were studied. Furthermore, the experimental results are in good agreement with numerical results of the liquid penetration through a series of pores. The numerical analysis was performed for a two-dimensional model that is based on the geometric features of the graphite foam sample and using the multiphase Volume-of-Fluid (VOF) method.
3

Ding, Changsong, Gaurav Soni, Payam Bozorgi, Brian Piorek, Carl D. Meinhart, and Noel C. MacDonald. "A Titanium Based Flat Heat Pipe." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68967.

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We are developing innovative heat pipes based on Nano-Structured Titania (NST) with a potential for high heat carrying capacity and high thermal conductivity. These heat pipes have a flat geometry as opposed to a cylindrical geometry found in conventional heat pipes. The flatness will enable a good contact with microprocessor chips and thus reduce the thermal contact resistance. We refer to it as a Thermal Ground Plane (TGP) because of its flat and thin geometry. It will provide the ability to cool the future generations of power intensive microprocessor chips and circuit boards in an efficient way. It also brings the potential to function in high temperature (>150°C) fields because of its high yield strength and compatibility [1]. The TGP is fabricated with Titanium. It adopts the recently developed high aspect ratio Ti processing techniques [2] and laser packaging techniques. The three main components of the TGP are 1) a fine wick structure based on arrays of high aspect ratio Ti pillars and hair like structures of Nano-Structured Titania (NST), 2) A shallow Ti cavity welded onto the wick structure and 3) the working fluid, water, sealed between the cavity and the wick. The heat carrying capacity and the thermal conductivity of a heat pipe are generally determined by the speed of capillary flow of the working fluid through its wick. The TGP wick has the potential to generate high flow rates and to meet the growing challenges faced by electronics cooling community. The TGP wick structure, developed by etching high aspect ratio pillars in a titanium substrate and growing nano scale hairs on the surface of the pillars, is super hydrophilic and capable of wicking water at velocities ∼ 10−2 m/s over distances of several centimeters. The thermal conductivity of the current TGP device was measured to be k = 350 W/m·K. The completed TGP device has the potential of attaining a higher conductivity by improving the wicking material and of carrying higher power density. Washburn equation [3] for dynamics of capillary flow has been employed to explain the results of our experiments. The experiment shows a good agreement with Washburn equation.
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King, Ryan M., Miguel Amaya, and Seung M. You. "Evaporative Cooling Performance of a Brazed Microporous Coating on an Aluminum Surface." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-85905.

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The effect of an aluminum microporous coating on evaporative cooling performance of water was studied. The coating consisted of aluminum powder brazed to a flat aluminum substrate. Coatings of average thicknesses of 175 μm, 270 μm, 900 μm, and of average aluminum particle sizes of 27 μm, 70 μm and 114 μm were tested. A hot water treatment of the coating insured repeatability of thermal performance. Wickability was measured and compared to Washburn’s equation for capillary flow. Evaporative cooling tests were then performed on coated and plain surfaces. The test surfaces were uniformly heated while kept vertically dipped in an isothermal pool of water. All microporous coatings increased evaporative heat transfer relative to that of the plain surface by their ability to wick fluid to the entire heated area. With particle size increase from 27 μm to 70 μm both the wickability and heat transfer were significantly increased, but no further significant gains in either were obtained with increase to 114 μm. The maximum heat transfer coefficient was increased ∼11 times and the temperature limit (dry-out) heat flux increased ∼10 times with the two larger particle sizes (70 μm and 114 μm). The heat transfer coefficient and dry-out heat flux similarly increased with thickness increase.
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Zheng, Leo, Ying Sun, Timothy Singler, Jeremias Libres, Siva Gurrum, and Patrick Thompson. "Modeling and Experiments of Underfill Flow in Large Dies With Non-Uniform Bump Patterns." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-69006.

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This paper presents numerical modeling and experimental results for the problem of underfill flow in a large die with a non-uniform bump pattern in a flip-chip packaging configuration. Two different 2-D flow models coupled with the volume-of-fluid (VOF) method are applied to track the underfill flow front during the simulation of flip-chip encapsulation. The first model employs the modified Washburn model and uses a time-dependent inlet velocity to account for the flow resistance across the gap direction in the presence of bump interconnects. The second model introduces a momentum source term in the Stokes equation to represent the gapwise resistance. Rheological properties, surface tension, and dynamic contact angles for an underfill material are experimentally determined. Simulation results based on the two models are compared with in-situ flow visualization conducted using bumped quartz dies. The comparison demonstrates the applicability of each model for simulating the underfill encapsulation process.
6

Choi, Changho, Chih-hung Chang, Shankar Krishnan, Terry J. Hendricks, and Ward TeGrotenhuis. "Capillary Rise and Evaporative Heat Transfer in Nano-Structured Multi-Mode Wicks." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-63776.

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Nanostructured films were successfully deposited on various wick samples including conventional screen materials, engineered single and dual-mode wicks which are specially designed to augment boiling heat transfer performance. Microreactor-assisted nanomaterial deposition, MAND™, was employed with a flow cell to deposit the nanostructures on large wick shims (4.3cm × 10.7cm). Capillary rise experiments, height based measurement and weight gain method, were performed to characterize wicking dynamics in nano-coated and “bare” capillary wicks with water and ethanol. The results indicate that nanocoated wick is most efficient for ethanol in terms of the enhancement of capillary force. Analytical and numerical analyses based on Lucas Washburn equation were performed to model the capillary rise. Data from the height measurement were in a good agreement with both numerical and analytical solutions. Capillary rise of water on engineered multi-mode wicks displayed a step-rise in the wicking front. Flow boiling tests were also performed to characterize heat transfer from nano-coated wicks for application in energy conversion systems as compact evaporators. Experimental results indicate that the nanostructured wicks enhance heat transfer, reduce superheat required and operate stably when compared with “bare” wicks and conventional microchannels.
7

Rahman, M. Shafiqur, and Uttam K. Chakravarty. "Characterizations of the Paper-Based Microfluidic Devices Used for Detecting Fentanyl and Related Synthetic Opioids." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-11581.

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Abstract The design and analysis of a paper-based microfluidic analytical device (μPAD) are presented in this paper for the detection of fentanyl and related synthetic opioids. Fentanyl, a synthetic opioid, is an extremely fast-acting synthetic narcotic analgesic having a high potency of approximately 100 to 200 times that of morphine. Detection of fentanyl can be done by colorimetric assays, i.e., spot tests with paper strips and μPADs which offer speed, simplicity of operation, portability, and affordability. The microfluidic behavior of liquid specimen and paper in the μPADs and test strips play a significant role in drug detection methods. Therefore, the study contains the fabrication of the test device using 3D printing and analysis of microfluidic behavior of the paper-based fentanyl test device. A multiphase computational fluid dynamics (CFD) model of a 3D microchannel is developed to evaluate the microfluidic properties. The CFD model incorporates the properties of cellulose and fentanyl solution to determine the flow parameters using the volume of fluid method. Wicking in the cellulose paper is studied analytically considering the Lucas-Washburn equation and Darcy’s law. Experiments with the fabricated μPAD and commercial test-kit samples are also conducted to compare the experimental results with the results for the flow parameters found from the numerical simulation.
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Suciu, Claudiu Valentin. "Thermal Effects on Nano-Energy Absorption Systems (Nano-EAS)." In 2008 Second International Conference on Integration and Commercialization of Micro and Nanosystems. ASMEDC, 2008. http://dx.doi.org/10.1115/micronano2008-70039.

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Development of intelligent and ecological energy absorption systems (EAS) is important to various fields such as automotive (vehicle suspensions, bumpers, engine mounts), construction (protections against seismic and wind-induced vibrations), and defense (parachuted objects, armors). Usual EAS use composites, shape-memory alloys and foams. Recently, liquid adsorption/desorption in/from nanoporous solids was employed to develop high-performance nano-EAS. Energy loss is based on the well-known capillary phenomenon: external work must be done to spread a non-wetting liquid on a solid surface. Nano-EAS provide considerably higher dissipated energies, about 1–10J/g at deformability of 30–70%, compared with the energy absorption of Ti-Ni alloys, about 0.01–0.05J/g at deformability of 5–8%. For water against hydrophobic nanoporous silica gel (artificial sand), the nano-EAS become ecological; they can be also made intelligent by thermo-electrical control. Relative to thermal effects, Qiao et al. have investigated, for nanoporous silica gel with insufficient coverage of the alkyl-based hydrophobic coating, the problem of hysteresis recovery by increasing the temperature in the range 20∼80°C. Energy loss capacity reduced severely after the first loading-unloading cycle, so, the hysteresis was found as irreversible. Shape of the first hysteresis, the accessible specific pore volume and the desorption pressure were almost unaffected by the temperature change. At temperature augmentation the second hysteresis was partially recovered and when the temperature exceeded 50°C the system became almost fully reusable. Water inflow was found as governed by Laplace-Washburn equation but the outflow process was perceived as thermally aided. On the other hand, Eroshenko et al. have contradictorily obtained for nanoporous silica gel with full coverage of the alkyl-based hydrophobic coating, a stable hysteresis at repeated working cycles. Adsorption pressure decreased and desorption pressure increased at temperature augmentation, this producing a reduction of the hysteresis area and damping. However, the accessible specific pore volume was found as thermally unaffected. Oppositely, both the in- and out-flows were found as governed by Laplace-Washburn equation. In this work, for nanoporous silica gels with partial and full coverage of the alkyl and fluorocarbon based hydrophobic coatings, the thermal effects on the hysteresis and damping performances are studied. Test rig used is a compression-decompression chamber introduced inside of an incubator that allows temperature adjustment in the range of −10∼50°C. Results reveal that, depending on the hydrophobic coating coverage, findings reported by Qiao et al. and Eroshenko et al. are in fact not contradictory but complementary. However, as expected, the accessible specific pore volume was found to decrease at temperature reduction. In order to explain all these apparently opposite experimental findings, a model based on the water cluster size distribution versus temperature, the pore size distribution of silica gel and the ability of water molecules to form hydrogen bonds with the uncovered hydroxyl groups on the solid surface is proposed.
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Friess, Brooks, and Mina Hoorfar. "Fluorescence Microscopy for the Measurement of the Surface Properties of the Gas Diffusion Layers of Fuel." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-39523.

Повний текст джерела
Стилі APA, Harvard, Vancouver, ISO та ін.
Анотація:
One of the major problems of current proton exchange membrane (PEM) fuel cells is water management. The gas diffusion layer (GDL) of the fuel cell plays an important role in water management since humidification and water removal are both achieved through the GDL. Various numerical models developed to illustrate the multiphase flow and transport in the fuel cell require the accurate measurement of the GDL properties (wettability and surface energy). In a recent study, the capillary penetration technique has been used to measure indirectly the wettability of the GDL based on the experimental height penetration of the sample liquid into the porous sample. In essence, a high resolution microscope/camera was used to detect the rate of penetrated height into the sample GDL. The shortcoming of this type of visualization is that it can only be used for thin hydrophilic GDL samples with zero Teflon loadings. For the thick and high Teflon loading GDLs, there is not enough contrast to detect the height of the penetrated liquid. In the real fuel cells, the GDLs are made of the micro-porous and macro-porous layers with an optimum Teflon loading. Therefore, it is required to develop a new experimental methodology capable of detecting the rate of penetration and as a result the wettability of GDLs samples used in fuel cells. In this paper, the fluorescence microscopy technique is integrated into the experimental setup of the capillary penetration method to improve the contrast between the wetted and non-wetted area. The fluorescence setup uses a powder die, dissolved in the test fluid, which is excited by a concentrated ultraviolet light illuminated in the vertical manner. To acquire the profile images of the penetrated liquid, an optical mirror was used. This new setup has the added advantage of providing a visual representation of the different regimes of penetration (e.g., the fingering effect reported for the pathways of the liquid penetrated into the GDLs) that are defined by the capillary number and mobility ratio of each fluid. Since the GDL samples used in this study are relatively hydrophobic (e.g., with 40% Teflon loadings), the pattern of liquid penetration is not uniform. Thus, an image analysis program was developed to determine the average height of penetration based on the area under the entire wetted area. The general Washburn equation was then used to fit the extracted height data and provide the average internal contact angle for each test liquid.

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