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Effects of surface topography and colloid particles on the evaporation kinetics of sessile droplets on superhydrophobic surfaces / Wei Xu in Journal of heat transfer, Vol. 134 N° 5 (Mai 2012) 

Public ISBD [article]  in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Titre : Effects of surface topography and colloid particles on the evaporation kinetics of sessile droplets on superhydrophobic surfaces Type de document : texte imprimé Auteurs : Wei Xu, Auteur ; Chang-Hwan Choi, Auteur Année de publication : 2012 Article en page(s) : 07 p. Note générale : heat transfer Langues : Anglais (eng) Mots-clés : sessile  droplet;  evaporation  kinetics;  colloids;  superhydrophobic  surface Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, the evaporation kinetics of microliter-sized sessile droplets of gold colloids (~250 nm in particle diameters) was experimentally studied on micropatterned superhydrophobic surfaces, compared with those of pure water on a planar hydrophobic surface. The structural microtopography of superhydrophobic surfaces was designed to have a constant air fraction (~0.8) but varying array patterns including pillars, lines, and wells. During evaporation in a room condition, the superhydrophobic surfaces exhibited a stronger pinning effect than a planar surface, especially in the initial evaporation stage, with significant variations by the surface topographies. Compared to a pure water droplet, colloids exhibited further promoted pinning effects, mainly in the later stage of evaporation. While the well-known evaporative mass transport law of sessile droplets (i.e., linear law of “V2/3[proportional]t”) was generally applicable to the superhydrophobic surfaces, much smaller evaporation rate constants were measured on the patterned superhydrophobic surfaces than on a planar hydrophobic surface. A colloidal droplet further showed lower evaporation rate constants than a pure water droplet as the concentration of particles in the droplets increased over the evaporation. Such transition was more dramatic on a planar surface than on the micropatterned surfaces. Whereas there was no clear correlation between evaporation mode and the evaporation rate observed on the superhydrophobic surfaces, the prominent decrease of the evaporation rate on the planar hydrophobic surface was accompanied with the onset of a second pinning mode. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...] [article] Effects of surface topography and colloid particles on the evaporation kinetics of sessile droplets on superhydrophobic surfaces [texte imprimé] / Wei Xu, Auteur ; Chang-Hwan Choi, Auteur . - 2012 . - 07 p. heat transfer Langues : Anglais (eng) in Journal of heat transfer > Vol. 134 N° 5 (Mai 2012) . - 07 p. Mots-clés : sessile  droplet;  evaporation  kinetics;  colloids;  superhydrophobic  surface Index. décimale : 536 Chaleur. Thermodynamique Résumé : In this paper, the evaporation kinetics of microliter-sized sessile droplets of gold colloids (~250 nm in particle diameters) was experimentally studied on micropatterned superhydrophobic surfaces, compared with those of pure water on a planar hydrophobic surface. The structural microtopography of superhydrophobic surfaces was designed to have a constant air fraction (~0.8) but varying array patterns including pillars, lines, and wells. During evaporation in a room condition, the superhydrophobic surfaces exhibited a stronger pinning effect than a planar surface, especially in the initial evaporation stage, with significant variations by the surface topographies. Compared to a pure water droplet, colloids exhibited further promoted pinning effects, mainly in the later stage of evaporation. While the well-known evaporative mass transport law of sessile droplets (i.e., linear law of “V2/3[proportional]t”) was generally applicable to the superhydrophobic surfaces, much smaller evaporation rate constants were measured on the patterned superhydrophobic surfaces than on a planar hydrophobic surface. A colloidal droplet further showed lower evaporation rate constants than a pure water droplet as the concentration of particles in the droplets increased over the evaporation. Such transition was more dramatic on a planar surface than on the micropatterned surfaces. Whereas there was no clear correlation between evaporation mode and the evaporation rate observed on the superhydrophobic surfaces, the prominent decrease of the evaporation rate on the planar hydrophobic surface was accompanied with the onset of a second pinning mode. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JHTRAO000134000005 [...]

Facile preparation of nanocryptomelane and its application in the treatment of aqueous solutions containing basic fuchsin / Wei Xu in Industrial & engineering chemistry research, Vol. 51 N° 50 (Décembre 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 50 (Décembre 2012) . - pp. 16188-16195 Titre : Facile preparation of nanocryptomelane and its application in the treatment of aqueous solutions containing basic fuchsin Type de document : texte imprimé Auteurs : Wei Xu, Auteur ; Zifeng Deng, Auteur ; Guangming Li, Auteur Année de publication : 2013 Article en page(s) : pp. 16188-16195 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Aqueous  solution  Preparation Résumé : Cryptomelane nanomaterials were synthesized by a facile redox―reflux method. The physicochemical properties of these composites were studied in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, laser Raman spectroscopy, thennogravimetric analysis (TGA), and N, adsorption-desorption techniques. The catalytic activities of nanocryptomelane were evaluated through treatment of aqueous solutions that contained basic fuchsin. In the case of basic fuchsin, the catalytic activity of synthetic nanocryptomelane was much higher than that of natural cryptomelane. Moreover, synthetic nanocryptomelane shows high stability and recyclability, has a high specific surface area, and is rich in mesopores. It could be anticipated that the specific surface area of the material had an obvious effect on the degradation of basic fuchsin. Kinetic studies indicated that the reaction follows the Langmuir―Hinshelwood model. The catalytic activities were found to be primarily correlated with the specific surface area. Overall, cryptomelane nanomaterials have great potential in the treatment of dye-containing wastewater. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=26732145 [article] Facile preparation of nanocryptomelane and its application in the treatment of aqueous solutions containing basic fuchsin [texte imprimé] / Wei Xu, Auteur ; Zifeng Deng, Auteur ; Guangming Li, Auteur . - 2013 . - pp. 16188-16195. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 50 (Décembre 2012) . - pp. 16188-16195 Mots-clés : Aqueous  solution  Preparation Résumé : Cryptomelane nanomaterials were synthesized by a facile redox―reflux method. The physicochemical properties of these composites were studied in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, laser Raman spectroscopy, thennogravimetric analysis (TGA), and N, adsorption-desorption techniques. The catalytic activities of nanocryptomelane were evaluated through treatment of aqueous solutions that contained basic fuchsin. In the case of basic fuchsin, the catalytic activity of synthetic nanocryptomelane was much higher than that of natural cryptomelane. Moreover, synthetic nanocryptomelane shows high stability and recyclability, has a high specific surface area, and is rich in mesopores. It could be anticipated that the specific surface area of the material had an obvious effect on the degradation of basic fuchsin. Kinetic studies indicated that the reaction follows the Langmuir―Hinshelwood model. The catalytic activities were found to be primarily correlated with the specific surface area. Overall, cryptomelane nanomaterials have great potential in the treatment of dye-containing wastewater. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=26732145

Measuring dielectric constant in highly conductive soils based on surface reflection coefficients / Renpeng Chen in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 12 (Décembre 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 12 (Décembre 2009) . - pp. 1883–1891 Titre : Measuring dielectric constant in highly conductive soils based on surface reflection coefficients Type de document : texte imprimé Auteurs : Renpeng Chen, Auteur ; Wei Xu, Auteur ; Yunmin Chen, Auteur Année de publication : 2010 Article en page(s) : pp. 1883–1891 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Soil  propertiesElectrical  conductivityCoefficientsReflection Résumé : In soils with high electrical conductivities, time domain reflectometry (TDR) principles fail to measure the apparent dielectric constant by travel time analysis. This limits the application of water content measurement of existing TDR technologies on those materials. This paper describes a new approach for determining the dielectric constants in highly conductive soils from surface reflections of TDR signals. The multiple reflections at the interfaces of impedance mismatches in the ASTM standard probe were studied. Extension rods were used to avoid the overlap of the reflections along the probe. A relationship between the reflection coefficient at the soil surface and the apparent dielectric constant of the soil was established theoretically and validated by laboratory experiments. Results indicate that the dielectric constant can be determined with reasonable accuracy from the surface reflection coefficient even for soils with high electrical conductivities, where the conventional travel time analysis fails. Compared with alternative approaches, such as based on inversion model, this new method offers high time efficiency in extending TDR applications in highly conductive soils. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000170 [article] Measuring dielectric constant in highly conductive soils based on surface reflection coefficients [texte imprimé] / Renpeng Chen, Auteur ; Wei Xu, Auteur ; Yunmin Chen, Auteur . - 2010 . - pp. 1883–1891. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 12 (Décembre 2009) . - pp. 1883–1891 Mots-clés : Soil  propertiesElectrical  conductivityCoefficientsReflection Résumé : In soils with high electrical conductivities, time domain reflectometry (TDR) principles fail to measure the apparent dielectric constant by travel time analysis. This limits the application of water content measurement of existing TDR technologies on those materials. This paper describes a new approach for determining the dielectric constants in highly conductive soils from surface reflections of TDR signals. The multiple reflections at the interfaces of impedance mismatches in the ASTM standard probe were studied. Extension rods were used to avoid the overlap of the reflections along the probe. A relationship between the reflection coefficient at the soil surface and the apparent dielectric constant of the soil was established theoretically and validated by laboratory experiments. Results indicate that the dielectric constant can be determined with reasonable accuracy from the surface reflection coefficient even for soils with high electrical conductivities, where the conventional travel time analysis fails. Compared with alternative approaches, such as based on inversion model, this new method offers high time efficiency in extending TDR applications in highly conductive soils. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000170

Numerical investigation of a centrifugal compressor with holed casing treatment / Wei Xu in Transactions of the ASME . Journal of engineering for gas turbines and power, Vol. 134 N° 4 (Avril 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 4 (Avril 2012) . - 04 p. Titre : Numerical investigation of a centrifugal compressor with holed casing treatment Type de document : texte imprimé Auteurs : Wei Xu, Auteur ; Tong Wang, Auteur ; Chuangang Gu, Auteur ; Liang Ding, Auteur Année de publication : 2012 Article en page(s) : 04 p. Note générale : Génie mécanique Langues : Anglais (eng) Mots-clés : Compressors  Flow  instability  Flow  simulation  Impellers  Numerical  analysis Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The holed casing treatment is a new type of casing treatment that has self-adaptability for a centrifugal compressor with unshrouded impeller. It was demonstrated experimentally and numerically that both the stall margin and the choked margin of the compressor were able to be expanded by the treatment. Numerical results indicate that there is reinjected flow in the holes when the compressor works at low flow rate conditions, and bypass flow at high flow rate conditions. The key principles for choosing the diameter and the radial position of the hole are presented in this paper. The hole's diameter is an important parameter for the holed casing treatment. Five numerical cases with different diameters (1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm) were carried out to compare the results. The reinjected flow enters into the impeller passage periodically and it tends to increase when the hole diameter gets larger. In the case of 2.5 mm, both the stall margin increment and the efficiency of the compressor were the highest among the five cases. Unsteady simulations suggest that the reinjected flow is not only periodic in time but also periodic in circumferential direction. This is the reason why only 2% of the flow amounts would get 20% of the working range expansion. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000004 [...] [article] Numerical investigation of a centrifugal compressor with holed casing treatment [texte imprimé] / Wei Xu, Auteur ; Tong Wang, Auteur ; Chuangang Gu, Auteur ; Liang Ding, Auteur . - 2012 . - 04 p. Génie mécanique Langues : Anglais (eng) in Transactions of the ASME . Journal of engineering for gas turbines and power > Vol. 134 N° 4 (Avril 2012) . - 04 p. Mots-clés : Compressors  Flow  instability  Flow  simulation  Impellers  Numerical  analysis Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The holed casing treatment is a new type of casing treatment that has self-adaptability for a centrifugal compressor with unshrouded impeller. It was demonstrated experimentally and numerically that both the stall margin and the choked margin of the compressor were able to be expanded by the treatment. Numerical results indicate that there is reinjected flow in the holes when the compressor works at low flow rate conditions, and bypass flow at high flow rate conditions. The key principles for choosing the diameter and the radial position of the hole are presented in this paper. The hole's diameter is an important parameter for the holed casing treatment. Five numerical cases with different diameters (1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm) were carried out to compare the results. The reinjected flow enters into the impeller passage periodically and it tends to increase when the hole diameter gets larger. In the case of 2.5 mm, both the stall margin increment and the efficiency of the compressor were the highest among the five cases. Unsteady simulations suggest that the reinjected flow is not only periodic in time but also periodic in circumferential direction. This is the reason why only 2% of the flow amounts would get 20% of the working range expansion. DEWEY : 620.1 ISSN : 0742-4795 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JETPEZ000134000004 [...]