Documents disponibles écrits par cet auteur

Adsorption behaviors and mechanisms of methyl orange on heat-treated palygorskite clays / Hao Chen in Industrial & engineering chemistry research, Vol. 51 N° 43 (Octobre 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 43 (Octobre 2012) . - pp. 14026–14036 Titre : Adsorption behaviors and mechanisms of methyl orange on heat-treated palygorskite clays Type de document : texte imprimé Auteurs : Hao Chen, Auteur ; Aiguo Zhong, Auteur ; Junyong Wu, Auteur Année de publication : 2013 Article en page(s) : pp. 14026–14036 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : Clay  mineral Résumé : Understanding completely the interaction of clay mineral and anionic dye is very important for the applications of clay minerals. In this paper, the adsorption behaviors of heat-treated palygorskite clays for methyl orange (MO) from an aqueous medium were studied using equilibrium batch and theoretic calculation techniques. The crystal structure and surface appearance of the heat-treated samples were studied using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The adsorption results reveal that a higher calcining temperature helps in improving removal performance of palygorskite clay for methyl orange. The isothermal adsorption experiments show that there is almost no adsorption at low dye concentrations but a sudden linear increase occurs when the dye concentration exceeds to a certain value. A lower change point is observed for 700 °C treated sample compared with that of the natural sample. The leaching of exchangeable Mg2+ ions located in palygorskite should be a key factor affecting the adsorption capacity. Both the experimental and theoretical studies suggest that the adsorption of MO onto heat-treated palygorskite clay is controlled by the two mechanisms: for samples treated at lower temperatures (<300 °C), the hydrogen bonding between oxygen groups of −SO3– (anionic head groups of MO) and H+ of both the bound zeolitic water and coordinated water should be important. While for samples calcined at higher temperature (>400 °C), electrostatic interaction between the dye–Mg2+ complexes and negatively charged surface of heat-treated palygorskite clay becomes dominant. In addition, the latter becomes stronger with the increasing the calcination temperature, which can be ascribed to the formation of a higher ratio of complexes and stronger negatively charged surface of the adsorbent caused by leaching of more metal ions. This work provides a deep insight into the interaction of heat-treated palygorskite clay and anionic dye, which paves the way for their practical applications in anionic dye adsorption. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie300702j [article] Adsorption behaviors and mechanisms of methyl orange on heat-treated palygorskite clays [texte imprimé] / Hao Chen, Auteur ; Aiguo Zhong, Auteur ; Junyong Wu, Auteur . - 2013 . - pp. 14026–14036. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 43 (Octobre 2012) . - pp. 14026–14036 Mots-clés : Clay  mineral Résumé : Understanding completely the interaction of clay mineral and anionic dye is very important for the applications of clay minerals. In this paper, the adsorption behaviors of heat-treated palygorskite clays for methyl orange (MO) from an aqueous medium were studied using equilibrium batch and theoretic calculation techniques. The crystal structure and surface appearance of the heat-treated samples were studied using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The adsorption results reveal that a higher calcining temperature helps in improving removal performance of palygorskite clay for methyl orange. The isothermal adsorption experiments show that there is almost no adsorption at low dye concentrations but a sudden linear increase occurs when the dye concentration exceeds to a certain value. A lower change point is observed for 700 °C treated sample compared with that of the natural sample. The leaching of exchangeable Mg2+ ions located in palygorskite should be a key factor affecting the adsorption capacity. Both the experimental and theoretical studies suggest that the adsorption of MO onto heat-treated palygorskite clay is controlled by the two mechanisms: for samples treated at lower temperatures (<300 °C), the hydrogen bonding between oxygen groups of −SO3– (anionic head groups of MO) and H+ of both the bound zeolitic water and coordinated water should be important. While for samples calcined at higher temperature (>400 °C), electrostatic interaction between the dye–Mg2+ complexes and negatively charged surface of heat-treated palygorskite clay becomes dominant. In addition, the latter becomes stronger with the increasing the calcination temperature, which can be ascribed to the formation of a higher ratio of complexes and stronger negatively charged surface of the adsorbent caused by leaching of more metal ions. This work provides a deep insight into the interaction of heat-treated palygorskite clay and anionic dye, which paves the way for their practical applications in anionic dye adsorption. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie300702j

Effects of blade wrap angle influencing a pump as turbine / Sun-Sheng Yang in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 6 (Juin 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 6 (Juin 2012) . - 08 p. Titre : Effects of blade wrap angle influencing a pump as turbine Type de document : texte imprimé Auteurs : Sun-Sheng Yang, Auteur ; Fan-Yu Kong, Auteur ; Hao Chen, Auteur Année de publication : 2012 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : pump  as  turbine;  blade  wrap  angle;  numerical  research;  performance  analysis;  hydraulic  loss  distribution Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A pump is not ideally designed to operate as a turbine. To improve the efficiency of a pump as turbine (PAT), the redesign of the PAT, according to the flow of the turbine, is required. The blade wrap angle is one of the main geometric parameters in impeller design. Therefore, an investigation into the blade wrap angle to the PAT's influence can be useful. In order to understand blade wrap angle to the influence of the PAT, this paper numerically investigated three different specific speeds of PATs with different blade wrap angles. The validity of numerical simulation was first confirmed through a comparison between numerical and experimental results. The performance change of the PATs with the blade wrap angle was acquired. A detailed hydraulic loss distribution and a theoretical analysis were performed to investigate the reasons for performance changes caused by the blade wrap angle. The results show that there is an optimal blade wrap angle for a PAT to achieve the highest efficiency and the optimal blade wrap angle decreases with an increasing specific speed. A performance analysis shows the PAT's flow versus pressure head (Q-H) and flow versus generated shaft power (Q-P) curves are lowered with the decrease of the blade wrap angle. The hydraulic loss distribution and theoretical analysis illustrate that it is the decrease of hydraulic loss within the impeller, together with the decrease of the theoretical head, that results in the performance decrease. The decrease of hydraulic loss within the impeller is attributed to the shortened impeller blade passage and the reduced velocity gradient within the impeller flow channel. With the decrease of the blade wrap angle, the slip factor of the PAT's impeller is decreased; therefore, its theoretical head is also decreased. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA4000134000006 [...] [article] Effects of blade wrap angle influencing a pump as turbine [texte imprimé] / Sun-Sheng Yang, Auteur ; Fan-Yu Kong, Auteur ; Hao Chen, Auteur . - 2012 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 6 (Juin 2012) . - 08 p. Mots-clés : pump  as  turbine;  blade  wrap  angle;  numerical  research;  performance  analysis;  hydraulic  loss  distribution Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A pump is not ideally designed to operate as a turbine. To improve the efficiency of a pump as turbine (PAT), the redesign of the PAT, according to the flow of the turbine, is required. The blade wrap angle is one of the main geometric parameters in impeller design. Therefore, an investigation into the blade wrap angle to the PAT's influence can be useful. In order to understand blade wrap angle to the influence of the PAT, this paper numerically investigated three different specific speeds of PATs with different blade wrap angles. The validity of numerical simulation was first confirmed through a comparison between numerical and experimental results. The performance change of the PATs with the blade wrap angle was acquired. A detailed hydraulic loss distribution and a theoretical analysis were performed to investigate the reasons for performance changes caused by the blade wrap angle. The results show that there is an optimal blade wrap angle for a PAT to achieve the highest efficiency and the optimal blade wrap angle decreases with an increasing specific speed. A performance analysis shows the PAT's flow versus pressure head (Q-H) and flow versus generated shaft power (Q-P) curves are lowered with the decrease of the blade wrap angle. The hydraulic loss distribution and theoretical analysis illustrate that it is the decrease of hydraulic loss within the impeller, together with the decrease of the theoretical head, that results in the performance decrease. The decrease of hydraulic loss within the impeller is attributed to the shortened impeller blade passage and the reduced velocity gradient within the impeller flow channel. With the decrease of the blade wrap angle, the slip factor of the PAT's impeller is decreased; therefore, its theoretical head is also decreased. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA4000134000006 [...]

Importance of cellulosic fines relative to the dewatering rates of fiber suspensions / Hao Chen in Industrial & engineering chemistry research, Vol. 48 N° 20 (Octobre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 20 (Octobre 2009) . - pp. 9106–9112 Titre : Importance of cellulosic fines relative to the dewatering rates of fiber suspensions Type de document : texte imprimé Auteurs : Hao Chen, Auteur ; Andrew Park, Auteur ; John A. Heitmann, Auteur Année de publication : 2010 Article en page(s) : pp. 9106–9112 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Cellulosic  fines  Fiber  suspensions Résumé : When cellulosic fines are present in significant amounts, they can have a dominant influence on dewatering. Pulp suspensions drain rapidly if the fines have been removed. In this study, the dependency of gravity dewatering rates on the level and properties of cellulosic fine matter was quantified. Bleached hardwood kraft pulp was used as a source of primary fines (collected before refining) and secondary fines (collected after refining of fines-free fiber suspensions). Fractions of fine matter also were obtained from chemithermomechanical (CTMP) pulp. Size distributions of these fines were characterized using a laser diffraction method. Results were explainable by a mechanism in which unattached fines are able to move relative to adjacent fibers during the dewatering and consolidation of a mat of fibers. Due to such movement, fines end up in locations where they plug drainage channels in the mat. The contribution of the fines to dewatering increased in inverse proportion to particle size and with increasing surface area, as calculated from the light scattering analysis. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9006613 [article] Importance of cellulosic fines relative to the dewatering rates of fiber suspensions [texte imprimé] / Hao Chen, Auteur ; Andrew Park, Auteur ; John A. Heitmann, Auteur . - 2010 . - pp. 9106–9112. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 20 (Octobre 2009) . - pp. 9106–9112 Mots-clés : Cellulosic  fines  Fiber  suspensions Résumé : When cellulosic fines are present in significant amounts, they can have a dominant influence on dewatering. Pulp suspensions drain rapidly if the fines have been removed. In this study, the dependency of gravity dewatering rates on the level and properties of cellulosic fine matter was quantified. Bleached hardwood kraft pulp was used as a source of primary fines (collected before refining) and secondary fines (collected after refining of fines-free fiber suspensions). Fractions of fine matter also were obtained from chemithermomechanical (CTMP) pulp. Size distributions of these fines were characterized using a laser diffraction method. Results were explainable by a mechanism in which unattached fines are able to move relative to adjacent fibers during the dewatering and consolidation of a mat of fibers. Due to such movement, fines end up in locations where they plug drainage channels in the mat. The contribution of the fines to dewatering increased in inverse proportion to particle size and with increasing surface area, as calculated from the light scattering analysis. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9006613

Optimum Trajectory Switching Control for Series-Parallel Resonant Converter / Hao Chen in IEEE transactions on industrial electronics, Vol. 53 N° 5 (Octobre 2006)

Public ISBD [article]  in IEEE transactions on industrial electronics > Vol. 53 N° 5 (Octobre 2006) . - 1555-1563 p. Titre : Optimum Trajectory Switching Control for Series-Parallel Resonant Converter Titre original : Commande Optima de Commutation de Trajectoire pour le Convertisseur Résonnant en Série-Parallèle Type de document : texte imprimé Auteurs : Hao Chen, Auteur ; Sng, Eng Kian Kenneth, Auteur ; Tseng, King-Jet Article en page(s) : 1555-1563 p. Note générale : Génie Electrique Langues : Anglais (eng) Mots-clés : Optimal  trajectory  control  Commande  optimale  de  trajectoire  Series-parallel  resonant  converter  Convertisseur  résonnant  en  série-parallèle Index. décimale : 621 Ingénierie mécanique en général. Technologie nucléaire. Ingénierie électrique. Machinerie Résumé : The series-parallel resonant converter (SPRC) is known to have combined merits of the series resonant converter (SRC) and PRC. However, the SPRC has a three-element LCC structure with complex transient dynamics, and without control of the resonant circuit's dynamics, the converter's closed-loop bandwidth to switching-frequency ratio will be much reduced compared to that of pulsewidth-modulation (PWM) converters. This paper presents the optimal trajectory enabling any SPRC's steady state be achieved within one cycle. Dynamics using the state-plane analysis is presented, and the optimal state trajectory for transients is derived. Experimental results with comparison to frequency control show much reduced resonant circuit response time for step changes in output voltage. This improved resonant circuit control allows subsequent current and voltage-loop controls of the SPRC to be treated as that of a conventional PWM voltage source. Le convertisseur résonnant en série-parallèle (SPRC) est connu pour avoir des mérites combinés du convertisseur résonnant de série (SRC) et de la RPC. Cependant, le SPRC a une structure du trois-élément LCC avec la dynamique passagère complexe, et sans commande de la dynamique de circuit résonnant, la largeur de bande en circuit fermé du convertisseur au rapport de commutation-fréquence sera beaucoup réduite comparée à celle des convertisseurs de la pulsewidth-modulation (PWM). Cet article présente la trajectoire optimale permettant l'état d'équilibre de n'importe quel SPRC soit réalisé à moins d'un cycle. La dynamique employant l'analyse d'état-avion est présentée, et la trajectoire optimale d'état pour des coupures est dérivée. Les résultats expérimentaux avec la comparaison à la commande de fréquence montrent beaucoup de temps de réponse réduit de circuit résonnant pour des changements d'étape de tension de rendement. Cette commande améliorée de circuit résonnant permet des commandes suivantes de courant et de tension-boucle du SPRC à traiter en tant que cela d'une source conventionnelle de tension de PWM. DEWEY : 621 ISSN : 0278-0046 [article] Optimum Trajectory Switching Control for Series-Parallel Resonant Converter = Commande Optima de Commutation de Trajectoire pour le Convertisseur Résonnant en Série-Parallèle [texte imprimé] / Hao Chen, Auteur ; Sng, Eng Kian Kenneth, Auteur ; Tseng, King-Jet . - 1555-1563 p. Génie Electrique Langues : Anglais (eng) in IEEE transactions on industrial electronics > Vol. 53 N° 5 (Octobre 2006) . - 1555-1563 p. Mots-clés : Optimal  trajectory  control  Commande  optimale  de  trajectoire  Series-parallel  resonant  converter  Convertisseur  résonnant  en  série-parallèle Index. décimale : 621 Ingénierie mécanique en général. Technologie nucléaire. Ingénierie électrique. Machinerie Résumé : The series-parallel resonant converter (SPRC) is known to have combined merits of the series resonant converter (SRC) and PRC. However, the SPRC has a three-element LCC structure with complex transient dynamics, and without control of the resonant circuit's dynamics, the converter's closed-loop bandwidth to switching-frequency ratio will be much reduced compared to that of pulsewidth-modulation (PWM) converters. This paper presents the optimal trajectory enabling any SPRC's steady state be achieved within one cycle. Dynamics using the state-plane analysis is presented, and the optimal state trajectory for transients is derived. Experimental results with comparison to frequency control show much reduced resonant circuit response time for step changes in output voltage. This improved resonant circuit control allows subsequent current and voltage-loop controls of the SPRC to be treated as that of a conventional PWM voltage source. Le convertisseur résonnant en série-parallèle (SPRC) est connu pour avoir des mérites combinés du convertisseur résonnant de série (SRC) et de la RPC. Cependant, le SPRC a une structure du trois-élément LCC avec la dynamique passagère complexe, et sans commande de la dynamique de circuit résonnant, la largeur de bande en circuit fermé du convertisseur au rapport de commutation-fréquence sera beaucoup réduite comparée à celle des convertisseurs de la pulsewidth-modulation (PWM). Cet article présente la trajectoire optimale permettant l'état d'équilibre de n'importe quel SPRC soit réalisé à moins d'un cycle. La dynamique employant l'analyse d'état-avion est présentée, et la trajectoire optimale d'état pour des coupures est dérivée. Les résultats expérimentaux avec la comparaison à la commande de fréquence montrent beaucoup de temps de réponse réduit de circuit résonnant pour des changements d'étape de tension de rendement. Cette commande améliorée de circuit résonnant permet des commandes suivantes de courant et de tension-boucle du SPRC à traiter en tant que cela d'une source conventionnelle de tension de PWM. DEWEY : 621 ISSN : 0278-0046

Removal capacity and adsorption mechanism of heat-treated palygorskite clay for methylene blue / Hao Chen in Chemical engineering journal, Vol. 174 N° 1 (Octobre 2011) 

Public ISBD [article]  in Chemical engineering journal > Vol. 174 N° 1 (Octobre 2011) . - pp.143–150 Titre : Removal capacity and adsorption mechanism of heat-treated palygorskite clay for methylene blue Type de document : texte imprimé Auteurs : Hao Chen, Auteur ; Jie Zhao, Auteur ; Aiguo Zhong, Auteur Année de publication : 2012 Article en page(s) : pp.143–150 Note générale : Génie chimique Langues : Anglais (eng) Mots-clés : Adsorption  Heat-treated  palygorskite  Methylene  blue  Dissolved  ions  Mechanism Résumé : In this work, palygorskite clay was activated by heat treatment method and its capacity for the removal of a typical cationic dye, methylene blue, was studied. The activated samples were characterized by XRD and BET techniques. The physical quantities including the cation exchange capacity (CEC) of the activated samples, the variation of pH during the adsorption process and the concentration of metal ions in the supernatant were also measured. The results show that the adsorption capacity of the heat-treated sample increases with temperature and reaches the maximum at 700 °C, and then decreases with further increasing temperature. In general, with the increasing calcined temperature, the variation trend of the adsorption capacity of activated samples for dye is accordant with that of CEC. The results of the metal ions leached from the adsorbent demonstrate the leaching amount of divalent ions (Mg2+, Ca2+) in all samples are significantly higher than that of univalent (Na+, K+) and trivalent ions (Fe3+, Al3+). In addition, the changing tendency of leaching amount of divalent ions with the increasing temperature is consistent with that of adsorption capacity of the heat-treated samples whether the dye solution is acidic, neutral or alkaline. The leaching of divalent ions should be the main factor affecting the adsorption capacity of heat-activated palygorskite for methylene blue. ISSN : 1385-8947 En ligne : http://www.sciencedirect.com/science/article/pii/S1385894711010205 [article] Removal capacity and adsorption mechanism of heat-treated palygorskite clay for methylene blue [texte imprimé] / Hao Chen, Auteur ; Jie Zhao, Auteur ; Aiguo Zhong, Auteur . - 2012 . - pp.143–150. Génie chimique Langues : Anglais (eng) in Chemical engineering journal > Vol. 174 N° 1 (Octobre 2011) . - pp.143–150 Mots-clés : Adsorption  Heat-treated  palygorskite  Methylene  blue  Dissolved  ions  Mechanism Résumé : In this work, palygorskite clay was activated by heat treatment method and its capacity for the removal of a typical cationic dye, methylene blue, was studied. The activated samples were characterized by XRD and BET techniques. The physical quantities including the cation exchange capacity (CEC) of the activated samples, the variation of pH during the adsorption process and the concentration of metal ions in the supernatant were also measured. The results show that the adsorption capacity of the heat-treated sample increases with temperature and reaches the maximum at 700 °C, and then decreases with further increasing temperature. In general, with the increasing calcined temperature, the variation trend of the adsorption capacity of activated samples for dye is accordant with that of CEC. The results of the metal ions leached from the adsorbent demonstrate the leaching amount of divalent ions (Mg2+, Ca2+) in all samples are significantly higher than that of univalent (Na+, K+) and trivalent ions (Fe3+, Al3+). In addition, the changing tendency of leaching amount of divalent ions with the increasing temperature is consistent with that of adsorption capacity of the heat-treated samples whether the dye solution is acidic, neutral or alkaline. The leaching of divalent ions should be the main factor affecting the adsorption capacity of heat-activated palygorskite for methylene blue. ISSN : 1385-8947 En ligne : http://www.sciencedirect.com/science/article/pii/S1385894711010205