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Celerity - amplitude relations for solitary waves on vertically falling films / Cesar E. Meza in Industrial & engineering chemistry research, Vol. 50 N° 23 (Décembre 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 23 (Décembre 2011) . - pp. 13258–13272 Titre : Celerity - amplitude relations for solitary waves on vertically falling films Type de document : texte imprimé Auteurs : Cesar E. Meza, Auteur ; Vemuri Balakotaiah, Auteur Année de publication : 2012 Article en page(s) : pp. 13258–13272 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Celerity  solitary  waves Résumé : Experimental data relating the amplitude and celerity of solitary waves on vertically falling and naturally excited films are presented over a wide of range of fluid properties and flow rates (2 < Ka < 3883, 0.08 < We < 35). It is found that for a fixed set of fluid properties (Ka) and flow rate (1/We), the celerity-amplitude relationship for all finite amplitude waves that exist on the film is nearly linear with a slope that decreases with the flow rate (1/We). For viscous fluids (2 < Ka < 129), the observed normalized maximum wave amplitude increased monotonically with the flow rate (1/We) and saturated at values around 3 (hmax ≈ 3) and found to be nearly independent of the fluid viscosity (Ka). For less viscous fluids (206 < Ka < 3883) the waves were found to be continuously evolving with maximum normalized amplitudes of about 10. A recently developed two equation h–q model is used to analyze the spatio-temporal dynamics of waves on the film. The model predictions corroborate the hypothesis that the existence of very large amplitude waves for less viscous fluids is due to the phenomenon of flow reversal (or existence of up-flows) near the wall. The model predicts a critical Ka value below which no flow reversal occurs. It is also shown that once the wave amplitude exceeds a critical value, the amplitude-celerity relationship is nearly linear for all solitary waves that exist on the film and is independent of the inlet forcing frequency or amplitude or initial conditions. Local bifurcation analysis in the traveling wave coordinate, computational results on extended domains with periodic inlet forcing, and computational results on finite domains with periodic boundary conditions are used to explain the experimentally observed wave celerity-ampliude relations on naturally excited films. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie2005803 [article] Celerity - amplitude relations for solitary waves on vertically falling films [texte imprimé] / Cesar E. Meza, Auteur ; Vemuri Balakotaiah, Auteur . - 2012 . - pp. 13258–13272. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 23 (Décembre 2011) . - pp. 13258–13272 Mots-clés : Celerity  solitary  waves Résumé : Experimental data relating the amplitude and celerity of solitary waves on vertically falling and naturally excited films are presented over a wide of range of fluid properties and flow rates (2 < Ka < 3883, 0.08 < We < 35). It is found that for a fixed set of fluid properties (Ka) and flow rate (1/We), the celerity-amplitude relationship for all finite amplitude waves that exist on the film is nearly linear with a slope that decreases with the flow rate (1/We). For viscous fluids (2 < Ka < 129), the observed normalized maximum wave amplitude increased monotonically with the flow rate (1/We) and saturated at values around 3 (hmax ≈ 3) and found to be nearly independent of the fluid viscosity (Ka). For less viscous fluids (206 < Ka < 3883) the waves were found to be continuously evolving with maximum normalized amplitudes of about 10. A recently developed two equation h–q model is used to analyze the spatio-temporal dynamics of waves on the film. The model predictions corroborate the hypothesis that the existence of very large amplitude waves for less viscous fluids is due to the phenomenon of flow reversal (or existence of up-flows) near the wall. The model predicts a critical Ka value below which no flow reversal occurs. It is also shown that once the wave amplitude exceeds a critical value, the amplitude-celerity relationship is nearly linear for all solitary waves that exist on the film and is independent of the inlet forcing frequency or amplitude or initial conditions. Local bifurcation analysis in the traveling wave coordinate, computational results on extended domains with periodic inlet forcing, and computational results on finite domains with periodic boundary conditions are used to explain the experimentally observed wave celerity-ampliude relations on naturally excited films. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie2005803

Estimation of Effective diffusivity of stored NOx in the barium phase of Pt / BaO / Al2O3 catalysts using TAP / Ashok Kumar in Industrial & engineering chemistry research, Vol. 49 N° 21 (Novembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10334-10340 Titre : Estimation of Effective diffusivity of stored NOx in the barium phase of Pt / BaO / Al2O3 catalysts using TAP Type de document : texte imprimé Auteurs : Ashok Kumar, Auteur ; Michael P. Harold, Auteur ; Vemuri Balakotaiah, Auteur Année de publication : 2011 Article en page(s) : pp. 10334-10340 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Catalyst  Diffusion  coefficient Résumé : A systematic study over Pt/BaO/Al2O3 powder catalyst is carried out using Temporal Analysis of Products (TAP) to estimate the effective diffusivity of stored NO, in the barium phase. The prenitration of PtBaO/ Al2O3 using sequential pulses of NO, followed by reduction with H2 results in the evolution of N2 and NH3. The reduction is carried out in the NOx transport limited regime in which diffusion of the stored NO, from BaO storage phase to Pt/BaO interface was determined to be the rate controlling process. The effluent profiles of N containing species (2N2 + NH3) were used to estimate stored NO, diffusivity in barium phase and the apparent activation energy. The activation energy (74-81 kJ/mol) is in good agreement with the estimated value of 75 kJ/mol from a recent NO, trap modeling study.1. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447924 [article] Estimation of Effective diffusivity of stored NOx in the barium phase of Pt / BaO / Al2O3 catalysts using TAP [texte imprimé] / Ashok Kumar, Auteur ; Michael P. Harold, Auteur ; Vemuri Balakotaiah, Auteur . - 2011 . - pp. 10334-10340. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 21 (Novembre 2010) . - pp. 10334-10340 Mots-clés : Catalyst  Diffusion  coefficient Résumé : A systematic study over Pt/BaO/Al2O3 powder catalyst is carried out using Temporal Analysis of Products (TAP) to estimate the effective diffusivity of stored NO, in the barium phase. The prenitration of PtBaO/ Al2O3 using sequential pulses of NO, followed by reduction with H2 results in the evolution of N2 and NH3. The reduction is carried out in the NOx transport limited regime in which diffusion of the stored NO, from BaO storage phase to Pt/BaO interface was determined to be the rate controlling process. The effluent profiles of N containing species (2N2 + NH3) were used to estimate stored NO, diffusivity in barium phase and the apparent activation energy. The activation energy (74-81 kJ/mol) is in good agreement with the estimated value of 75 kJ/mol from a recent NO, trap modeling study.1. ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=23447924

Modeling studies on lean NOx reduction by a sequence of LNT – SCR bricks / Arun S. Kota in Industrial & engineering chemistry research, Vol. 51 N° 19 (Mai 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 19 (Mai 2012) . - pp. 6686–6696 Titre : Modeling studies on lean NOx reduction by a sequence of LNT – SCR bricks Type de document : texte imprimé Auteurs : Arun S. Kota, Auteur ; Dan Luss, Auteur ; Vemuri Balakotaiah, Auteur Année de publication : 2012 Article en page(s) : pp. 6686–6696 Note générale : Industrial chemistry Langues : Anglais (eng) Mots-clés : NOx  Selective  catalytic  reduction Résumé : Several experimental studies have been conducted to determine the NOx reduction by a series of LNT (lean NOx trap) and SCR (selective catalytic reduction) catalytic bricks. An important goal is to minimize the required precious metal loading in the LNT while keeping the NOx emission below a specified level. We present a mathematical model of this system using hydrogen as the reductant. Simulations are used to determine the influence of the architecture of the LNT–SCR bricks, nonuniform precious metal loading in the LNT bricks, and the cycle time at temperatures in the range of 200–350 °C. The simulations lead to the following observations: (a) Low temperature reduction is the limiting step in the optimization of precious group metal (PGM) loading in LNT. (b) The NOx conversion increases as the number of the sequential bricks (with total length fixed) increase and reaches an asymptotic limit. From a practical point of view, there is little incentive in using more than two sequential pairs. (c) Nonuniform precious metal loading of the LNT bricks results in only a minor improvement in the deNOx performance. (d) The cycle time has a significant impact on the NOx conversion. In the simulated example, the NOx conversion at low temperatures is increased by about 15–20% by reducing the cycle time by a factor of 2. (e) Even at low temperature operation, diffusional limitations in the washcoat are most likely to be important in the LNT but not in the SCR operation. The NOx conversion and ammonia selectivity are reduced when washcoat diffusion is dominant in the LNT. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie300190c [article] Modeling studies on lean NOx reduction by a sequence of LNT – SCR bricks [texte imprimé] / Arun S. Kota, Auteur ; Dan Luss, Auteur ; Vemuri Balakotaiah, Auteur . - 2012 . - pp. 6686–6696. Industrial chemistry Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 19 (Mai 2012) . - pp. 6686–6696 Mots-clés : NOx  Selective  catalytic  reduction Résumé : Several experimental studies have been conducted to determine the NOx reduction by a series of LNT (lean NOx trap) and SCR (selective catalytic reduction) catalytic bricks. An important goal is to minimize the required precious metal loading in the LNT while keeping the NOx emission below a specified level. We present a mathematical model of this system using hydrogen as the reductant. Simulations are used to determine the influence of the architecture of the LNT–SCR bricks, nonuniform precious metal loading in the LNT bricks, and the cycle time at temperatures in the range of 200–350 °C. The simulations lead to the following observations: (a) Low temperature reduction is the limiting step in the optimization of precious group metal (PGM) loading in LNT. (b) The NOx conversion increases as the number of the sequential bricks (with total length fixed) increase and reaches an asymptotic limit. From a practical point of view, there is little incentive in using more than two sequential pairs. (c) Nonuniform precious metal loading of the LNT bricks results in only a minor improvement in the deNOx performance. (d) The cycle time has a significant impact on the NOx conversion. In the simulated example, the NOx conversion at low temperatures is increased by about 15–20% by reducing the cycle time by a factor of 2. (e) Even at low temperature operation, diffusional limitations in the washcoat are most likely to be important in the LNT but not in the SCR operation. The NOx conversion and ammonia selectivity are reduced when washcoat diffusion is dominant in the LNT. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie300190c