The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Mingyao Zhang - One of the best experts on this subject based on the ideXlab platform.
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Experimental and Model Investigations on Gas Mixing Behaviors of Spout-fluid Beds
International Journal of Chemical Reactor Engineering, 2007Co-Authors: Wenqi Zhong, Mingyao Zhang, Baosheng Jin, Rui XiaoAbstract:Steady-state tracer Gas measurements were carried out to study the Gas Mixing behaviors in a spout-fluid bed with a cross section of 0.3 m x 0.03 m and height of 2 m. Two different tracer Gases were simultaneously injected, one was injected into the spouting Gas flow and the other was injected into the fluidizing Gas flow. Radial tracer Gas concentrations at various bed elevations under different flow patterns were measured. The mechanism of Gas Mixing was discussed based on the racer Gas concentrations and the flow patterns recorded by a high-resolution digital CCD camera. It was found that Gas Mixing in spout-fluid beds was due to both convection and dispersion. A three-region Mixing model was developed to describe the Gas Mixing in the spout-fluid bed. The spout jet region and the boundary region were modeled with a mass transfer model; the annular region was modeled with a dispersion model. Effects of spouting Gas and fluidizing Gas flow rate on the Gas exchange between the spout jet and the annular dense region, and the Gas dispersion in the annular dense region were examined with flow patterns. The results showed that increase in spouting Gas velocity and fluidizing Gas flow rate could both promote the Gas Mixing in spout-fluid beds. The Gas-solid flow pattern transited from internal jet to spouting to spout-fluidizing, and the Gases were better mixed. But the Gases became poorly mixed when the flow pattern transited from stable flow to instable flow.
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Experimental study of Gas Mixing in a spout‐fluid bed
AIChE Journal, 2006Co-Authors: Wenqi Zhong, Rui Xiao, Mingyao ZhangAbstract:Gas Mixing in a spout-fluid bed with a cross section of 0.3 × 0.03 m and height of 2 m was investigated by simultaneously injecting two different tracer Gases. One was injected into the spouting Gas flow and the other was injected into the fluidizing Gas flow. Steady-state tracer Gas measurements were carried out to obtained radial tracer Gas concentrations at various bed elevations. Effects of two important operating parameters—spouting Gas velocity and fluidizing Gas flow rate—on the Gas Mixing were discussed with flow patterns recorded by a high-resolution digital CCD camera. The results show that increasing spouting Gas velocity and fluidizing Gas flow rate can both promote the Gas Mixing in spout-fluid beds. Increasing fluidizing Gas flow rate is the more effective way, given that a satisfactory Mixing condition at a relatively low bed height can be obtained by increasing the fluidizing Gas flow rate. For both cases, it is difficult to obtain a good Mixing condition in the wall layers. Besides, the mechanism of Gas Mixing was preliminarily discussed. Results indicate that Gas Mixing in the spout-fluid bed is caused by both convection and diffusion. Diffusion other than molecular diffusion should not be neglected, especially at high spouting Gas velocity or fluidizing Gas flow rate. © 2005 American Institute of Chemical Engineers AIChE J, 2006
Ola Hjalmarson - One of the best experts on this subject based on the ideXlab platform.
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Gas Mixing Efficiency in Preterm Infants: Which Multibreath Nitrogen Washout Index is Best? 1740
Pediatric Research, 1998Co-Authors: Hongqian Shao, Kenneth Sandberg, Ola HjalmarsonAbstract:Aims: We have recently shown that moment ratios (MR) and lung clearence index (LCI) of multibreath nitrogen washouts (MBNW) are sensitive indicators of Gas Mixing inefficiency in infants with mild chronic lung disease (CLD). The aim of the present study was to improve the calculation of MR and compare the improved index with the original and with other measures of Gas Mixing efficiency based on MBNW in preterm infants.
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Impaired Gas Mixing and low lung volume in preterm infants with mild chronic lung disease.
Pediatric Research, 1998Co-Authors: Hongqian Shao, Kenneth Sandberg, Ola HjalmarsonAbstract:The aim of this study was to assess the possible role of Gas Mixing inefficiency in spontaneously breathing infants with mild chronic lung disease (CLD) of prematurity in relation to changes in other functional parameters. A simple bedside technique for recording and analysis of multiple breath nitrogen washout curves was applied together with occlusion mechanics. Fifteen preterm infants with mild or moderately severe CLD were studied at a mean postconceptional age of 35 wk, together with 15 healthy preterm infants at the same maturity. All infants breathed spontaneously, and the test was performed by a continuous bypass flow system, connected to a face mask, a pneumotachograph, and a nitrogen meter. The results showed impaired Gas Mixing with moment ratios above the 95th percentile of the normal group in 11/15 infants with CLD. Functional residual capacity (FRC) was low in 13/15 infants, but specific compliance and resistance of the respiratory system did not differ between the groups. As FRC and moment ratios were not correlated, it is suggested that they may reflect different aspects of the pathophysiology in CLD. It is concluded that low FRC and disturbed Gas Mixing are characteristic disturbances in CLD at different degrees of severity. The multiple breath nitrogen washout test, followed by moment analysis of end-tidal nitrogen concentrations, is a simple and sensitive method for detection of these disturbances and for monitoring purposes.
Kenneth Sandberg - One of the best experts on this subject based on the ideXlab platform.
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Gas Mixing Efficiency in Preterm Infants: Which Multibreath Nitrogen Washout Index is Best? 1740
Pediatric Research, 1998Co-Authors: Hongqian Shao, Kenneth Sandberg, Ola HjalmarsonAbstract:Aims: We have recently shown that moment ratios (MR) and lung clearence index (LCI) of multibreath nitrogen washouts (MBNW) are sensitive indicators of Gas Mixing inefficiency in infants with mild chronic lung disease (CLD). The aim of the present study was to improve the calculation of MR and compare the improved index with the original and with other measures of Gas Mixing efficiency based on MBNW in preterm infants.
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Impaired Gas Mixing and low lung volume in preterm infants with mild chronic lung disease.
Pediatric Research, 1998Co-Authors: Hongqian Shao, Kenneth Sandberg, Ola HjalmarsonAbstract:The aim of this study was to assess the possible role of Gas Mixing inefficiency in spontaneously breathing infants with mild chronic lung disease (CLD) of prematurity in relation to changes in other functional parameters. A simple bedside technique for recording and analysis of multiple breath nitrogen washout curves was applied together with occlusion mechanics. Fifteen preterm infants with mild or moderately severe CLD were studied at a mean postconceptional age of 35 wk, together with 15 healthy preterm infants at the same maturity. All infants breathed spontaneously, and the test was performed by a continuous bypass flow system, connected to a face mask, a pneumotachograph, and a nitrogen meter. The results showed impaired Gas Mixing with moment ratios above the 95th percentile of the normal group in 11/15 infants with CLD. Functional residual capacity (FRC) was low in 13/15 infants, but specific compliance and resistance of the respiratory system did not differ between the groups. As FRC and moment ratios were not correlated, it is suggested that they may reflect different aspects of the pathophysiology in CLD. It is concluded that low FRC and disturbed Gas Mixing are characteristic disturbances in CLD at different degrees of severity. The multiple breath nitrogen washout test, followed by moment analysis of end-tidal nitrogen concentrations, is a simple and sensitive method for detection of these disturbances and for monitoring purposes.
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Surfactant improves Gas Mixing and alveolar ventilation in preterm lambs.
Pediatric research, 1991Co-Authors: Kenneth Sandberg, Karl-erik Edberg, William Benton, Ants R. Silberberg, Malgorzata Sladek, Hakan SundellAbstract:ABSTRACT: Prophylactic treatment with ovine surfactant was evaluated in preterm lambs at risk for development of hyaline membrane disease. Eight mechanically ventilated newborn lambs were treated before delivery and 10 served as controls (gestational age 129–131 d). Lung mechanics, functional residual capacity, alveolar ventilation, efficiency of ventilation, and distribution of ventilation were tested using pressure, flow, and nitrogen elimination (nitrogen washout during 100% oxygen breathing) measurements in the endotracheal tube. The surfactant-treated animals showed significantly improved Gas Mixing efficiency in the lung with improved alveolar ventilation. Single exponential washout pattern dominated in both groups. Adequate functional residual capacity was established earlier after birth in the treated lambs than in the control animals. Lung mechanics in the treated group showed significant improvement in dynamic lung compliance. Surfactant treatment also improved Gas exchange and reduced respirator pressure requirement. We speculate that the main functional effect of surfactant treatment in preterm lambs at risk to develop hyaline membrane disease is to maintain the patency of the peripheral airways in the lung, which improves diffusive Gas Mixing, alveolar ventilation, and Gas exchange. The techniques used in this study should also be useful to evaluate lung function in preterm human infants after specific adaptation of the equipment size.
Wenqi Zhong - One of the best experts on this subject based on the ideXlab platform.
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Experimental and Model Investigations on Gas Mixing Behaviors of Spout-fluid Beds
International Journal of Chemical Reactor Engineering, 2007Co-Authors: Wenqi Zhong, Mingyao Zhang, Baosheng Jin, Rui XiaoAbstract:Steady-state tracer Gas measurements were carried out to study the Gas Mixing behaviors in a spout-fluid bed with a cross section of 0.3 m x 0.03 m and height of 2 m. Two different tracer Gases were simultaneously injected, one was injected into the spouting Gas flow and the other was injected into the fluidizing Gas flow. Radial tracer Gas concentrations at various bed elevations under different flow patterns were measured. The mechanism of Gas Mixing was discussed based on the racer Gas concentrations and the flow patterns recorded by a high-resolution digital CCD camera. It was found that Gas Mixing in spout-fluid beds was due to both convection and dispersion. A three-region Mixing model was developed to describe the Gas Mixing in the spout-fluid bed. The spout jet region and the boundary region were modeled with a mass transfer model; the annular region was modeled with a dispersion model. Effects of spouting Gas and fluidizing Gas flow rate on the Gas exchange between the spout jet and the annular dense region, and the Gas dispersion in the annular dense region were examined with flow patterns. The results showed that increase in spouting Gas velocity and fluidizing Gas flow rate could both promote the Gas Mixing in spout-fluid beds. The Gas-solid flow pattern transited from internal jet to spouting to spout-fluidizing, and the Gases were better mixed. But the Gases became poorly mixed when the flow pattern transited from stable flow to instable flow.
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Experimental study of Gas Mixing in a spout‐fluid bed
AIChE Journal, 2006Co-Authors: Wenqi Zhong, Rui Xiao, Mingyao ZhangAbstract:Gas Mixing in a spout-fluid bed with a cross section of 0.3 × 0.03 m and height of 2 m was investigated by simultaneously injecting two different tracer Gases. One was injected into the spouting Gas flow and the other was injected into the fluidizing Gas flow. Steady-state tracer Gas measurements were carried out to obtained radial tracer Gas concentrations at various bed elevations. Effects of two important operating parameters—spouting Gas velocity and fluidizing Gas flow rate—on the Gas Mixing were discussed with flow patterns recorded by a high-resolution digital CCD camera. The results show that increasing spouting Gas velocity and fluidizing Gas flow rate can both promote the Gas Mixing in spout-fluid beds. Increasing fluidizing Gas flow rate is the more effective way, given that a satisfactory Mixing condition at a relatively low bed height can be obtained by increasing the fluidizing Gas flow rate. For both cases, it is difficult to obtain a good Mixing condition in the wall layers. Besides, the mechanism of Gas Mixing was preliminarily discussed. Results indicate that Gas Mixing in the spout-fluid bed is caused by both convection and diffusion. Diffusion other than molecular diffusion should not be neglected, especially at high spouting Gas velocity or fluidizing Gas flow rate. © 2005 American Institute of Chemical Engineers AIChE J, 2006
Piero Salatino - One of the best experts on this subject based on the ideXlab platform.
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Laser diagnostics of hydrodynamics and Gas-Mixing induced by bubble bursting at the surface of Gas-fluidized beds
Chemical Engineering Science, 2007Co-Authors: Roberto Solimene, Antonio Marzocchella, Raffaele Ragucci, Piero SalatinoAbstract:Gas Mixing in the splash zone of Gas-fluidized bed reactors plays an important role in fluidized bed processes where fast homogeneous Gasphase reactions take place. An example is represented by the fluidized bed combustion of high-volatile solid fuels, where the large contribution to overall heat release due to homogeneous combustion of volatile matter and the “stratified” combustion pattern emphasize the importance of Mixing/segregation phenomena in the splash zone. Gas Mixing and hydrodynamics in the splash zone are determined by the complex interaction between bursting bubbles, the mainstream Gas and the bed solids. As a first step toward comprehensive characterization of hydrodynamics and Gas Mixing in the splash zone of a Gas fluidized bed, the present paper addresses the flow structures and the Gas Mixing patterns associated with the eruption of isolated bubbles at the surface of an incipiently fluidized bed. These are investigated by a combination of non-intrusive optical diagnostic techniques, namely planar laser light scattering (PLLS) and planar laser induced fluorescence (PLIF). The first is based on the use of a non-diffusive tracer (fine solid particles). The second is based on the use of a diffusive Gaseous tracer (acetone). The two techniques provide complementary tools to assess the detailed structure of the Gas and particle flow fields and the macro- and microMixing patterns associated with bubble bursting. The application of the two techniques to the analysis of events associated with the eruption of isolated bubbles proved to be successful. Results highlighted that the basic flow structure generated by bubble bursting is a toroidal vortex ring. The uprise velocity of the vortex and the Gas entrainment rate from the mainstream have been determined from results obtained with both the PLLS and PLIF measurements as a function of the size of the bursting bubble. MacroMixing, determined by Gas entrainment, and microMixing, related to molecular diffusion, have been quantitatively assessed by the combined analysis of tracer concentration maps obtained with the PLLS and PLIF techniques. The relevance of the observed hydrodynamics and Gas Mixing patterns to the kinetics of fast Gas-phase chemical reactions and to the performance of the splash zone of a fluidized bed as a homogeneous reactor is discussed, with a focus on volatile matter burn-out in fluidized bed combustors
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Flow Structures and Gas-Mixing Induced by Bubble Bursting at the Surface of an Incipiently Gas-Fluidized Bed
Industrial & Engineering Chemistry Research, 2004Co-Authors: Roberto Solimene, Antonio Marzocchella, Raffaele Ragucci, Piero SalatinoAbstract:Flow structures and Gas-Mixing induced in the splash zone of a fluidized bed reactor by bubble bursting at the bed surface were investigated. A planar laser light scattering technique based on a no...
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Gas-Mixing in Bubbling Fluidized Bed Combustors: Hydrodynamics and MacroMixing Associated With Bubble Bursting at the Bed Surface
17th International Conference on Fluidized Bed Combustion, 2003Co-Authors: Roberto Solimene, Antonio Marzocchella, Piero Salatino, Raffaele RagucciAbstract:Gas-Mixing phenomena may play a significant role in fluidized bed combustion of solid fuels. Issues associated with Gas Mixing include: a) effectiveness of mass transfer between the bubble and the emulsion phases in the bed; b) degree of Mixing between segregated Gaseous streams in plume-like or bubbly flow in the bottom bed; c) extent of Mixing between segregated Gaseous pockets/streams in the splashing zone or in the upper freeboard. Among the others, issues b) and c) turn out to be relevant to fluidized bed combustion of high-volatile solid fuels (biomass, RDF, etc.). In this case, the rate of Gas Mixing often overcomes intrinsic kinetics as the rate-controlling step in volatile matter burn-out, especially under “stratified” combustion conditions. Despite several and significant contributions to the subject, understanding of Gas-Mixing in bubbling fluidized beds is still poor and calls for additional investigation. The present work aims at investigating Gas-Mixing in bubbling fluidized bed with specific reference to the above issue c). A laser assisted imaging technique has been used to characterize the hydrodynamic patterns associated with the bursting of either isolated bubbles or couples of closely time-delayed bubbles at the surface of a fluidized bed. Quantitative image analysis procedures were exploited in order to assess parameters defining the general fluid-dynamic behaviour and macroMixing of the bubble-generated Gas pockets with the mainstream Gas. The formation of toroidal flow structures upon bubble bursting is highlighted in the case of isolated bubbles. The toroidal pockets entrain mainstream Gas and grow accordingly while rising along the splash zone. Toroidal flow structures are observed also in the case of couples of closely time-delayed bubbles, but interference between leading and trailing pockets leads to more complex structures characterized by multiple incoherent eddies. The relevance of macroMixing to volatile matter burning under conditions of stratified fluidized bed combustion is assessed and discussed.Copyright © 2003 by ASME
