Documents disponibles écrits par cet auteur

Batch reactors for hydrogen production / David L. Damm in Industrial & engineering chemistry research, Vol. 48 N° 12 (Juin 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 12 (Juin 2009) . - pp. 5610–5623 Titre : Batch reactors for hydrogen production : theoretical analysis and experimental characterization Type de document : texte imprimé Auteurs : David L. Damm, Auteur ; Andrei G. Fedorov, Auteur Année de publication : 2009 Article en page(s) : pp. 5610–5623 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Transient  batch-style  reactors  Hydrogen  production Résumé : Transient batch-style reactors (CHAMP) were recently shown to be an attractive alternative to continuous-flow reactors for hydrogen production in portable and distributed applications, and idealized kinetic reactor models were used to analyze the performance characteristics. Here, we expand this analysis with the development of a comprehensive batch reactor model which accounts for the effects of mass transport limitations on reactor performance. The relationships between system design parameters and the rate-limiting processes that govern reactor output are identified and mapped out. Additionally, two modes of operation of either constant-volume or constant-pressure reactors are investigated. In constant-volume mode, the residence time is precisely controlled to reach a desired operating state in a trade-off between efficiency and power output without compressing the content of the reaction chamber. In constant-pressure mode, the volume of the reactor is actively reduced by moving a piston along the trajectory that maintains the operating pressure at its maximum allowable value thus enhancing the reactor throughput. Complementary to the theoretical analysis, we report on the development and experimental characterization of two test reactors. The first reactor is a constant-volume batch reactor (no permeable membrane) and provides data on the transient evolution of species concentrations within the reaction chamber. The second reactor incorporates a hydrogen permeable membrane and allows for both constant-volume and variable-volume operation. The experimental data obtained using these reactors are used to validate the predictive value of the reactor model developed in the present study. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8015126 [article] Batch reactors for hydrogen production : theoretical analysis and experimental characterization [texte imprimé] / David L. Damm, Auteur ; Andrei G. Fedorov, Auteur . - 2009 . - pp. 5610–5623. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 12 (Juin 2009) . - pp. 5610–5623 Mots-clés : Transient  batch-style  reactors  Hydrogen  production Résumé : Transient batch-style reactors (CHAMP) were recently shown to be an attractive alternative to continuous-flow reactors for hydrogen production in portable and distributed applications, and idealized kinetic reactor models were used to analyze the performance characteristics. Here, we expand this analysis with the development of a comprehensive batch reactor model which accounts for the effects of mass transport limitations on reactor performance. The relationships between system design parameters and the rate-limiting processes that govern reactor output are identified and mapped out. Additionally, two modes of operation of either constant-volume or constant-pressure reactors are investigated. In constant-volume mode, the residence time is precisely controlled to reach a desired operating state in a trade-off between efficiency and power output without compressing the content of the reaction chamber. In constant-pressure mode, the volume of the reactor is actively reduced by moving a piston along the trajectory that maintains the operating pressure at its maximum allowable value thus enhancing the reactor throughput. Complementary to the theoretical analysis, we report on the development and experimental characterization of two test reactors. The first reactor is a constant-volume batch reactor (no permeable membrane) and provides data on the transient evolution of species concentrations within the reaction chamber. The second reactor incorporates a hydrogen permeable membrane and allows for both constant-volume and variable-volume operation. The experimental data obtained using these reactors are used to validate the predictive value of the reactor model developed in the present study. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8015126

Comparative assessment of batch reactors for scalable hydrogen production / David L. Damm in Industrial & engineering chemistry research, Vol. 47 n°14 (Juillet 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°14 (Juillet 2008) . - p. 4665–4674 Titre : Comparative assessment of batch reactors for scalable hydrogen production Type de document : texte imprimé Auteurs : David L. Damm, Auteur ; Andrei G. Fedorov, Auteur Année de publication : 2008 Article en page(s) : p. 4665–4674 Note générale : Bibliogr. p. 4673-4674 Langues : Anglais (eng) Mots-clés : Batch  reactors;  Scalable  hydrogen;  Numerical  simulation Résumé : A new concept of a variable volume batch reactor, CO2/H2 active membrane piston (CHAMP), is introduced for scalable hydrogen production for portable and distributed applications. The conceptual design and operating principles of the CHAMP reactor are discussed, aiming at precise control of residence time and optimal performance. A simplified reactor model is formulated, and the operation of the idealized reactor is numerically simulated. In the ideal limit of no heat or mass transfer limitations, the hydrogen yield rate and efficiency of the CHAMP reactor are shown to exceed that of a comparable, traditional continuous-flow (CF) design. In the presence of transport limitations, the relative performance enhancement enabled by the CHAMP reactor is even greater. Additionally, the transient nature of the CHAMP reactor makes it particularly suited for applications with varying power demands, such as in transportation, and its stackable design makes it highly scalable across a wide range of power requirements. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800294y [article] Comparative assessment of batch reactors for scalable hydrogen production [texte imprimé] / David L. Damm, Auteur ; Andrei G. Fedorov, Auteur . - 2008 . - p. 4665–4674. Bibliogr. p. 4673-4674 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°14 (Juillet 2008) . - p. 4665–4674 Mots-clés : Batch  reactors;  Scalable  hydrogen;  Numerical  simulation Résumé : A new concept of a variable volume batch reactor, CO2/H2 active membrane piston (CHAMP), is introduced for scalable hydrogen production for portable and distributed applications. The conceptual design and operating principles of the CHAMP reactor are discussed, aiming at precise control of residence time and optimal performance. A simplified reactor model is formulated, and the operation of the idealized reactor is numerically simulated. In the ideal limit of no heat or mass transfer limitations, the hydrogen yield rate and efficiency of the CHAMP reactor are shown to exceed that of a comparable, traditional continuous-flow (CF) design. In the presence of transport limitations, the relative performance enhancement enabled by the CHAMP reactor is even greater. Additionally, the transient nature of the CHAMP reactor makes it particularly suited for applications with varying power demands, such as in transportation, and its stackable design makes it highly scalable across a wide range of power requirements. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie800294y

Fuel reformation and hydrogen generation with direct droplet impingement reactors / Mark J. Varady in Industrial & engineering chemistry research, Vol. 50 N° 16 (Août 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9502-9513 Titre : Fuel reformation and hydrogen generation with direct droplet impingement reactors : model formulation and validation Type de document : texte imprimé Auteurs : Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur Année de publication : 2011 Article en page(s) : pp. 9502-9513 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Modeling  Reactor  Droplet  Hydrogen  production  Fuel Résumé : Onboard fuel reforming to produce hydrogen for portable fuel cell applications has been widely studied because the liquid has a high volumetric density as an energy storage medium. Several portable fuel reforming devices presented in the literature attempt to scale down the designs of traditional large-scale unit operations, an approach that becomes suboptimal as the size of the application is reduced. Unique reactor designs in which the various unit operations are combined in a synergistic manner are required to achieve higher energy densities and more compact reactors. Spraying a finely atomized liquid directly onto a hot catalyst is one such method that has been experimentally demonstrated. This work focuses on developing a fundamental understanding of this approach and optimizing it by utilizing a droplet generator array with precise control over the droplet spating, diameter, velocity, and trajectory, thus providing ultimate control over the reactor performance. The regular nature of the droplet generator array also enables modeling on a reactor-unit-cell basis with minimal empiricism, which can be used to optimize the reactor performance. The steady-state unit-cell model developed in this work accounts for the transport and evaporation of the droplet stream, impingement and subsequent film accumulation and vaporization, and gas-phase transport and reaction. The key components of the model were validated using relevant results from the literature to establish confidence in applying the complete model to predict reactor performance. Further, a reactor prototype mimicking the reactor unit cell used in the simulations was constructed and used to experimentally validate the comprehensive transport-reaction model for the specific case of methanol steam reforming, In a companion article, this complete model was used to study the effects of reactor operating parameters on conversion selectivity, and power density, aiming at an optimal reactor design. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425191 [article] Fuel reformation and hydrogen generation with direct droplet impingement reactors : model formulation and validation [texte imprimé] / Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur . - 2011 . - pp. 9502-9513. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9502-9513 Mots-clés : Modeling  Reactor  Droplet  Hydrogen  production  Fuel Résumé : Onboard fuel reforming to produce hydrogen for portable fuel cell applications has been widely studied because the liquid has a high volumetric density as an energy storage medium. Several portable fuel reforming devices presented in the literature attempt to scale down the designs of traditional large-scale unit operations, an approach that becomes suboptimal as the size of the application is reduced. Unique reactor designs in which the various unit operations are combined in a synergistic manner are required to achieve higher energy densities and more compact reactors. Spraying a finely atomized liquid directly onto a hot catalyst is one such method that has been experimentally demonstrated. This work focuses on developing a fundamental understanding of this approach and optimizing it by utilizing a droplet generator array with precise control over the droplet spating, diameter, velocity, and trajectory, thus providing ultimate control over the reactor performance. The regular nature of the droplet generator array also enables modeling on a reactor-unit-cell basis with minimal empiricism, which can be used to optimize the reactor performance. The steady-state unit-cell model developed in this work accounts for the transport and evaporation of the droplet stream, impingement and subsequent film accumulation and vaporization, and gas-phase transport and reaction. The key components of the model were validated using relevant results from the literature to establish confidence in applying the complete model to predict reactor performance. Further, a reactor prototype mimicking the reactor unit cell used in the simulations was constructed and used to experimentally validate the comprehensive transport-reaction model for the specific case of methanol steam reforming, In a companion article, this complete model was used to study the effects of reactor operating parameters on conversion selectivity, and power density, aiming at an optimal reactor design. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425191

Fuel reformation and hydrogen generation with direct droplet impingement reactors / Mark J. Varady in Industrial & engineering chemistry research, Vol. 50 N° 16 (Août 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9514-9524 Titre : Fuel reformation and hydrogen generation with direct droplet impingement reactors : parametric study and design considerations for portable methanol steam reformers Type de document : texte imprimé Auteurs : Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur Année de publication : 2011 Article en page(s) : pp. 9514-9524 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Water  vapor  Design  Reactor  Droplet  Hydrogen  production  Fuel Résumé : In a companion article (Varady and Fedorov Ind. Eng. Chem. Res. 2011, DOI: 10.1021/ie200563e), the concept of a direct droplet impingement reactor (DDIR) was introduced as a promising approach to liquid fuel reformation for distributed hydrogen generation. Considering the overall device as an array of unit cells enabled simplified modeling of the device on a unit-cell basis. In this study, the unit-cell model is utilized to study the effects of the important reactor operating parameters for the specific case of methanol steam reforming. The performance of the baseline DDIR is compared to the ideal limit of an isothermal plug-flow reactor (PFR). The effects of DDIR shape, size, heat input and location, and droplet initial conditions were varied from the baseline design to identify possible performance improvements. It was found that the selectivity displays a distinct marimum at a Pedet number (Pe) of ∼3 because of the interplay between back-diffusion of the products and thermal resistance of the catalyst bed. The spatial heating distribution also plays a key role, where an optimized matching of the heat input locations to the areas of heat consumption due to liquid vaporization and endothermic reaction results in an improved reactor performance, albeit at the penalty of a more complex reactor design and increased cost. Impingement of the droplet stream on the catalyst interface is necessary for proper operation, which requires certain initial droplet conditions to be satisfied, as expressed in the form of an operating regime map. Although the results are presented only for methanol steam reforming, the DDIR model is comprehensive and sufficiently general in terms of incorporated physical phenomena that it should be useful for developing similar operating criteria for other fuels and reactions requiring vaporization of a liquid feed followed by reaction over a fixed catalyst bed. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425192 [article] Fuel reformation and hydrogen generation with direct droplet impingement reactors : parametric study and design considerations for portable methanol steam reformers [texte imprimé] / Mark J. Varady, Auteur ; Andrei G. Fedorov, Auteur . - 2011 . - pp. 9514-9524. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 16 (Août 2011) . - pp. 9514-9524 Mots-clés : Water  vapor  Design  Reactor  Droplet  Hydrogen  production  Fuel Résumé : In a companion article (Varady and Fedorov Ind. Eng. Chem. Res. 2011, DOI: 10.1021/ie200563e), the concept of a direct droplet impingement reactor (DDIR) was introduced as a promising approach to liquid fuel reformation for distributed hydrogen generation. Considering the overall device as an array of unit cells enabled simplified modeling of the device on a unit-cell basis. In this study, the unit-cell model is utilized to study the effects of the important reactor operating parameters for the specific case of methanol steam reforming. The performance of the baseline DDIR is compared to the ideal limit of an isothermal plug-flow reactor (PFR). The effects of DDIR shape, size, heat input and location, and droplet initial conditions were varied from the baseline design to identify possible performance improvements. It was found that the selectivity displays a distinct marimum at a Pedet number (Pe) of ∼3 because of the interplay between back-diffusion of the products and thermal resistance of the catalyst bed. The spatial heating distribution also plays a key role, where an optimized matching of the heat input locations to the areas of heat consumption due to liquid vaporization and endothermic reaction results in an improved reactor performance, albeit at the penalty of a more complex reactor design and increased cost. Impingement of the droplet stream on the catalyst interface is necessary for proper operation, which requires certain initial droplet conditions to be satisfied, as expressed in the form of an operating regime map. Although the results are presented only for methanol steam reforming, the DDIR model is comprehensive and sufficiently general in terms of incorporated physical phenomena that it should be useful for developing similar operating criteria for other fuels and reactions requiring vaporization of a liquid feed followed by reaction over a fixed catalyst bed. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=24425192

Thermal characterization of interlayer microfluidic cooling of three-dimensional integrated circuits with nonuniform heat flux / Yoon Jo Kim in Journal of heat transfer, Vol. 132 N° 4 (n° spécial) (Avril 2010) 

Public ISBD [article]  in Journal of heat transfer > Vol. 132 N° 4 (n° spécial) (Avril 2010) . - pp. [041009-1/9] Titre : Thermal characterization of interlayer microfluidic cooling of three-dimensional integrated circuits with nonuniform heat flux Type de document : texte imprimé Auteurs : Yoon Jo Kim, Auteur ; Yogendra K. Joshi, Auteur ; Andrei G. Fedorov, Auteur Article en page(s) : pp. [041009-1/9] Note générale : Physique Langues : Anglais (eng) Mots-clés : Microchannel  Microfluidic  cooling  Three-dimensional  IC  Nonuniform  heat  flux  Single-phase  Two-phase  Pressure  drop Index. décimale : 536 Chaleur. Thermodynamique Résumé : It is now widely recognized that the three-dimensional (3D) system integration is a key enabling technology to achieve the performance needs of future microprocessor integrated circuits (ICs). To provide modular thermal management in 3D-stacked ICs, the interlayer microfluidic cooling scheme is adopted and analyzed in this study focusing on a single cooling layer performance. The effects of cooling mode (single-phase versus phase-change) and stack/layer geometry on thermal management performance are quantitatively analyzed, and implications on the through-silicon-via scaling and electrical interconnect congestion are discussed. Also, the thermal and hydraulic performance of several two-phase refrigerants is discussed in comparison with single-phase cooling. The results show that the large internal pressure and the pumping pressure drop are significant limiting factors, along with significant mass flow rate maldistribution due to the presence of hot-spots. Nevertheless, two-phase cooling using R123 and R245ca refrigerants yields superior performance to single-phase cooling for the hot-spot fluxes approaching ~300 W/cm2. In general, a hybrid cooling scheme with a dedicated approach to the hot-spot thermal management should greatly improve the two-phase cooling system performance and reliability by enabling a cooling-load-matched thermal design and by suppressing the mass flow rate maldistribution within the cooling layer. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...] [article] Thermal characterization of interlayer microfluidic cooling of three-dimensional integrated circuits with nonuniform heat flux [texte imprimé] / Yoon Jo Kim, Auteur ; Yogendra K. Joshi, Auteur ; Andrei G. Fedorov, Auteur . - pp. [041009-1/9]. Physique Langues : Anglais (eng) in Journal of heat transfer > Vol. 132 N° 4 (n° spécial) (Avril 2010) . - pp. [041009-1/9] Mots-clés : Microchannel  Microfluidic  cooling  Three-dimensional  IC  Nonuniform  heat  flux  Single-phase  Two-phase  Pressure  drop Index. décimale : 536 Chaleur. Thermodynamique Résumé : It is now widely recognized that the three-dimensional (3D) system integration is a key enabling technology to achieve the performance needs of future microprocessor integrated circuits (ICs). To provide modular thermal management in 3D-stacked ICs, the interlayer microfluidic cooling scheme is adopted and analyzed in this study focusing on a single cooling layer performance. The effects of cooling mode (single-phase versus phase-change) and stack/layer geometry on thermal management performance are quantitatively analyzed, and implications on the through-silicon-via scaling and electrical interconnect congestion are discussed. Also, the thermal and hydraulic performance of several two-phase refrigerants is discussed in comparison with single-phase cooling. The results show that the large internal pressure and the pumping pressure drop are significant limiting factors, along with significant mass flow rate maldistribution due to the presence of hot-spots. Nevertheless, two-phase cooling using R123 and R245ca refrigerants yields superior performance to single-phase cooling for the hot-spot fluxes approaching ~300 W/cm2. In general, a hybrid cooling scheme with a dedicated approach to the hot-spot thermal management should greatly improve the two-phase cooling system performance and reliability by enabling a cooling-load-matched thermal design and by suppressing the mass flow rate maldistribution within the cooling layer. DEWEY : 536 ISSN : 0022-1481 En ligne : http://asmedl.aip.org/vsearch/servlet/VerityServlet?KEY=JHTRAO&ONLINE=YES&smode= [...]