Documents disponibles écrits par cet auteur

Effect of particle porosity on hysteresis in trickle-bed reactors / rabindranath Maiti in Industrial & engineering chemistry research, Vol. 47 n°21 (Novembre 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 n°21 (Novembre 2008) . - p. 8126–8135 Titre : Effect of particle porosity on hysteresis in trickle-bed reactors Type de document : texte imprimé Auteurs : rabindranath Maiti, Auteur ; Arnab Atta, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2008 Article en page(s) : p. 8126–8135 Note générale : chemical engineering Langues : Anglais (eng) Mots-clés : HydrodynamicsParticle  porosity Résumé : Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs. View: PDF | PDF w/ Links | Full Text HTML En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8003539 [article] Effect of particle porosity on hysteresis in trickle-bed reactors [texte imprimé] / rabindranath Maiti, Auteur ; Arnab Atta, Auteur ; K. D. P. Nigam, Auteur . - 2008 . - p. 8126–8135. chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 n°21 (Novembre 2008) . - p. 8126–8135 Mots-clés : HydrodynamicsParticle  porosity Résumé : Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs. View: PDF | PDF w/ Links | Full Text HTML En ligne : http://pubs.acs.org/doi/abs/10.1021/ie8003539

Experimental study on pressure drop and heat transfer of turbulent flow in tube in tube helical heat exchanger / Monisha Mridha Mandal 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. 9318–9324 Titre : Experimental study on pressure drop and heat transfer of turbulent flow in tube in tube helical heat exchanger Type de document : texte imprimé Auteurs : Monisha Mridha Mandal, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2010 Article en page(s) : pp. 9318–9324 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Turbulent  flow  Heat  transfer  Fluid  flow  Reynolds  numbers Résumé : In the present study, experiments were conducted for the first time in tube in tube helical heat exchanger at the pilot plant scale to investigate the fluid flow and heat transfer under turbulent flow conditions. The experiments were carried out with hot compressed air in the inner tube and cooling water in the outer tube in the countercurrent mode of operation. The flow rate of compressed air flowing in the inner tube was varied for Reynolds numbers from 14 000 to 86 000. The pressure of compressed air was varied from 10 to 30 kgf/cm2. The friction factor and Nusselt number values for compressed air flowing in the inner tube were calculated for elevated pressure and compared with the experimental data reported in the literature at ambient conditions. Most of the works reported in the literature on heat transfer in coiled tubes have been carried out considering wall boundary conditions of either constant heat flux or constant wall temperature. In the present work, heat transfer calculations were based on physically realistic condition of fluid to fluid heat transfer. The inner tube Nusselt number of compressed air in the present study was found to be slightly higher than the data reported in the literature for ambient conditions while the friction factor values are within the range reported in the literature for ambient conditions. The friction factor as well as Nusselt number calculated for cooling water flowing in the outer tube was higher than the existing literature data. On the basis of the experimental results, new correlations for friction factor and Nusselt number in the inner as well as outer tubes have been developed. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9002393 [article] Experimental study on pressure drop and heat transfer of turbulent flow in tube in tube helical heat exchanger [texte imprimé] / Monisha Mridha Mandal, Auteur ; K. D. P. Nigam, Auteur . - 2010 . - pp. 9318–9324. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 20 (Octobre 2009) . - pp. 9318–9324 Mots-clés : Turbulent  flow  Heat  transfer  Fluid  flow  Reynolds  numbers Résumé : In the present study, experiments were conducted for the first time in tube in tube helical heat exchanger at the pilot plant scale to investigate the fluid flow and heat transfer under turbulent flow conditions. The experiments were carried out with hot compressed air in the inner tube and cooling water in the outer tube in the countercurrent mode of operation. The flow rate of compressed air flowing in the inner tube was varied for Reynolds numbers from 14 000 to 86 000. The pressure of compressed air was varied from 10 to 30 kgf/cm2. The friction factor and Nusselt number values for compressed air flowing in the inner tube were calculated for elevated pressure and compared with the experimental data reported in the literature at ambient conditions. Most of the works reported in the literature on heat transfer in coiled tubes have been carried out considering wall boundary conditions of either constant heat flux or constant wall temperature. In the present work, heat transfer calculations were based on physically realistic condition of fluid to fluid heat transfer. The inner tube Nusselt number of compressed air in the present study was found to be slightly higher than the data reported in the literature for ambient conditions while the friction factor values are within the range reported in the literature for ambient conditions. The friction factor as well as Nusselt number calculated for cooling water flowing in the outer tube was higher than the existing literature data. On the basis of the experimental results, new correlations for friction factor and Nusselt number in the inner as well as outer tubes have been developed. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie9002393

(Gas)-liquid-solid circulating fluidized bed reactors / Arnab Atta in Industrial & engineering chemistry research, Vol. 48 N° 17 (Septembre 2009) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 48 N° 17 (Septembre 2009) . - pp. 7876–7892 Titre : (Gas)-liquid-solid circulating fluidized bed reactors : characteristics and applications Type de document : texte imprimé Auteurs : Arnab Atta, Auteur ; S. A. Razzak, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2009 Article en page(s) : pp. 7876–7892 Note générale : Chemical engineering Langues : Anglais (eng) Mots-clés : Circulating  fluidized  beds  Gas-solid  circulating  fluidized  beds  Gas-liquid-solid  circulating  fluidized  beds Résumé : Accepting considerable advantages of circulating fluidized beds (CFBs) over the conventional fluidized beds, there has been numerous studies on CFBs concentrating primarily on the development of gas−solid circulating fluidized beds (GSCFBs). However a substantial amount of research has also been devoted to other two types of CFBs, namely liquid−solid and gas−liquid−solid circulating fluidized beds (LS and GLSCFBs). In this effort, an attempt has been made to summarize and review the research and progresses made on the last two types of CFBs since the highlighting of their hydrodynamics and potential applications in various industries by Zhu et al. [Can. J. Chem. Eng. 2000, 78, 82−94]. The issues associated with its hydrodynamics, scale-up, and design have been discussed with a re-emphasis on its potential application for various cost-effective processes. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900163t [article] (Gas)-liquid-solid circulating fluidized bed reactors : characteristics and applications [texte imprimé] / Arnab Atta, Auteur ; S. A. Razzak, Auteur ; K. D. P. Nigam, Auteur . - 2009 . - pp. 7876–7892. Chemical engineering Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 48 N° 17 (Septembre 2009) . - pp. 7876–7892 Mots-clés : Circulating  fluidized  beds  Gas-solid  circulating  fluidized  beds  Gas-liquid-solid  circulating  fluidized  beds Résumé : Accepting considerable advantages of circulating fluidized beds (CFBs) over the conventional fluidized beds, there has been numerous studies on CFBs concentrating primarily on the development of gas−solid circulating fluidized beds (GSCFBs). However a substantial amount of research has also been devoted to other two types of CFBs, namely liquid−solid and gas−liquid−solid circulating fluidized beds (LS and GLSCFBs). In this effort, an attempt has been made to summarize and review the research and progresses made on the last two types of CFBs since the highlighting of their hydrodynamics and potential applications in various industries by Zhu et al. [Can. J. Chem. Eng. 2000, 78, 82−94]. The issues associated with its hydrodynamics, scale-up, and design have been discussed with a re-emphasis on its potential application for various cost-effective processes. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie900163t

Liquid – liquid mixing in coiled flow inverter / Monisha Mridha Mandal 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. 13230-13235 Titre : Liquid – liquid mixing in coiled flow inverter Type de document : texte imprimé Auteurs : Monisha Mridha Mandal, Auteur ; Palka Aggarwal, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2012 Article en page(s) : pp. 13230-13235 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Mixing Résumé : The mixing of liquids is a common operation in process industries such as refineries and chemical and pharmaceutical industries, etc. However, the problem of mixing of different liquids has not been rigorously characterized. Therefore, the objective of this paper is to investigate liquid―liquid mixing in a novel coiled flow inverter (CFI). The device works on the principle of flow inversion which is achieved by bending a coiled tube to 90° at equidistant length. In the present study, velocity field and scalar concentration distribution of liquids were characterized. The mixing performances and pressure drop in CFI was investigated and compared with that of a straight, coiled tube and helical element mixer (HEM) for a liquid flow range of 98 ≤ Re ≤ 1020. CFI exhibits significant mixing of two liquids with negligible change in pressure drop as compared to a coiled tube as well as a HEM. The present study reveals that CFI is an efficient device for the mixing of two liquids in process industries. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=25267478 [article] Liquid – liquid mixing in coiled flow inverter [texte imprimé] / Monisha Mridha Mandal, Auteur ; Palka Aggarwal, Auteur ; K. D. P. Nigam, Auteur . - 2012 . - pp. 13230-13235. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 23 (Décembre 2011) . - pp. 13230-13235 Mots-clés : Mixing Résumé : The mixing of liquids is a common operation in process industries such as refineries and chemical and pharmaceutical industries, etc. However, the problem of mixing of different liquids has not been rigorously characterized. Therefore, the objective of this paper is to investigate liquid―liquid mixing in a novel coiled flow inverter (CFI). The device works on the principle of flow inversion which is achieved by bending a coiled tube to 90° at equidistant length. In the present study, velocity field and scalar concentration distribution of liquids were characterized. The mixing performances and pressure drop in CFI was investigated and compared with that of a straight, coiled tube and helical element mixer (HEM) for a liquid flow range of 98 ≤ Re ≤ 1020. CFI exhibits significant mixing of two liquids with negligible change in pressure drop as compared to a coiled tube as well as a HEM. The present study reveals that CFI is an efficient device for the mixing of two liquids in process industries. DEWEY : 660 ISSN : 0888-5885 En ligne : http://cat.inist.fr/?aModele=afficheN&cpsidt=25267478

Liquid-Phase Residence Time Distribution for Two-Phase Flow in Coiled Flow Inverter / Subhashini Vashisth in Industrial & engineering chemistry research, Vol. 47 N°10 (Mai 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N°10 (Mai 2008) . - p. 3630–3638 Titre : Liquid-Phase Residence Time Distribution for Two-Phase Flow in Coiled Flow Inverter Type de document : texte imprimé Auteurs : Subhashini Vashisth, Auteur ; K. D. P. Nigam, Auteur Année de publication : 2008 Article en page(s) : p. 3630–3638 Langues : Anglais (eng) Mots-clés : The  coiled  flow  inverter  --  Liquid-phase  residence  time  distribution(RTD)  ;  Gas  -liquid  ;  newtonian  fluids Résumé : The coiled flow inverter (CFI) is an innovative device, which has potential for the intensification of processes currently carried out in conventional mixers. Step response experiments were carried out in a CFI to study liquid-phase residence time distribution (RTD) for gas−liquid flow under the conditions of both negligible and significant molecular diffusion using Newtonian fluids. A total of 16 CFIs of different curvature ratios ranging from 6.7 to 20, dimensionless pitch from 1 to 2.5, and number of bends from 1 to 15 were investigated. The range of Dean numbers for the gas and the liquid phase was varied from 235 to 1180 and 3.16 to 1075, respectively. The reduction in dispersion number is nearly 2.6 times for two-phase flow in CFI with 15 number of bends as compared to a straight helix under identical process conditions. A modified axial dispersion model is proposed to describe the RTD. The efficiency of the device is characterized by a mixing criterion. En ligne : https://pubs.acs.org/doi/abs/10.1021/ie070447h [article] Liquid-Phase Residence Time Distribution for Two-Phase Flow in Coiled Flow Inverter [texte imprimé] / Subhashini Vashisth, Auteur ; K. D. P. Nigam, Auteur . - 2008 . - p. 3630–3638. Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N°10 (Mai 2008) . - p. 3630–3638 Mots-clés : The  coiled  flow  inverter  --  Liquid-phase  residence  time  distribution(RTD)  ;  Gas  -liquid  ;  newtonian  fluids Résumé : The coiled flow inverter (CFI) is an innovative device, which has potential for the intensification of processes currently carried out in conventional mixers. Step response experiments were carried out in a CFI to study liquid-phase residence time distribution (RTD) for gas−liquid flow under the conditions of both negligible and significant molecular diffusion using Newtonian fluids. A total of 16 CFIs of different curvature ratios ranging from 6.7 to 20, dimensionless pitch from 1 to 2.5, and number of bends from 1 to 15 were investigated. The range of Dean numbers for the gas and the liquid phase was varied from 235 to 1180 and 3.16 to 1075, respectively. The reduction in dispersion number is nearly 2.6 times for two-phase flow in CFI with 15 number of bends as compared to a straight helix under identical process conditions. A modified axial dispersion model is proposed to describe the RTD. The efficiency of the device is characterized by a mixing criterion. En ligne : https://pubs.acs.org/doi/abs/10.1021/ie070447h