Rotating packed bed(RPB) is one of the most effective gas–liquid mass transfer enhancement reactors, its effective specific mass transfer area(ae) is critical to understand the mass transfer process. By using the NaO...Rotating packed bed(RPB) is one of the most effective gas–liquid mass transfer enhancement reactors, its effective specific mass transfer area(ae) is critical to understand the mass transfer process. By using the NaOH–CO_(2) chemical absorption method, the aevalues of three RPB reactors with different rotor sizes were measured under different operation conditions. The results showed that the high gravity factor and liquid flow rate were major affecting factors, while the gas flow rate exhibited minor influence.The radius of packing is the dominant equipment factor to affect aevalue. The results indicated that the contact area depends on the dispersion of the liquid phase, thus the centrifugal force of rotating packed bed greatly influenced the aevalue. Moreover, the measured ae/ap(effective specific mass transfer area/specific surface area of packing) values were fitted with dimensionless correlation formulas. The unified correlation formula with dimensionless bed size parameter can well predict the experimental data and the prediction errors were within 15%.展开更多
Thermal Energy Storage is becoming a necessary component of sustainable energy production systems as it helps alleviate intrinsic limitations of Renewable Energy Sources, such as intermittent use and mismatch between ...Thermal Energy Storage is becoming a necessary component of sustainable energy production systems as it helps alleviate intrinsic limitations of Renewable Energy Sources, such as intermittent use and mismatch between power demand and supply. This paper discusses a packed bed thermocline tank as a thermal energy storage solution. Firstly, this paper presents the development of a numerical model calculating heat transfers within the tank, based on a discretization over several nodes and the nodal formulation of the heat balance equation. The model considers a filler material and a heat transferring fluid and uses the finite difference method to calculate the temperature evolution of the two media across the tank. The model was validated with two different packed bed systems from the literature during a discharging process, presenting a good fit with the experimental results. Secondly, the experimental packed bed is presented and characterized for a charging cycle from ambient temperature to approximately 180?C. The charging experiment was accurately reproduced with the numerical model requiring minimal computational time. Two additional charging modes were simulated with different inlet HTF conditions: constant temperature and varying temperature following the profile produced by a thermal solar collector field. The temperature profiles obtained from the three charging modes were analysed and compared to each other. The proposed numerical and experimental tools will be used in future studies for a better understanding of the design and operating conditions of packed bed thermal energy storage systems.展开更多
The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios(N = D/d b 8) where the local phenomena of channeling near the wall and backflow in the bed are dominant. Th...The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios(N = D/d b 8) where the local phenomena of channeling near the wall and backflow in the bed are dominant. The recent"solid particle" meshing method is too complicated for mesh generation, especially for non-spherical particles in large random packed beds, which seriously hinders its development. In this work, a novel high-fidelity mesh model is proposed for simulation of fixed bed reactors by combining the immersed boundary and adaptive meshing methods. This method is suitable for different shapes of particles, which ingeniously avoids handling the complex "contact point" problem. Several packed beds with two different shapes of particles are investigated with this model, and the local flow in the bed is simulated without geometrical simplification. The predicted pressure drop across the fixed bed and heat transfer of the single particle are in good agreement with the corresponding empirical relations. Compared with spherical particles, the packed bed packing with pentaphyllous particles has lower pressure drop and better heat/mass transfer performance, and it shows that this method can be used for the screening of particle shapes in a fixed bed.展开更多
Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly throug...Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.展开更多
Owing to its high heat storage capacity and fast heat transfer rate,packed bed latent heat storage(LHS)is considered as a promising method to store thermal energy.In a packed bed,the wall effect can impact the packing...Owing to its high heat storage capacity and fast heat transfer rate,packed bed latent heat storage(LHS)is considered as a promising method to store thermal energy.In a packed bed,the wall effect can impact the packing arrangement of phase change material(PCM)capsules,inducing radial porosity oscillation.In this study,an actual-arrangement-based three-dimensional packed bed LHS model was built to consider the radial porosity oscillation.Its fluid flow and heat transfer were analyzed.With different cylindrical sub-surfaces intercepted along the radial direction in the packed bed,the corresponding relationships between the arrangement of capsules and porosity oscillation were identified.The oscillating distribution of radial porosity led to a non-uniform distribution of heat transfer fluid(HTF)velocity.As a result,radial temperature distributions and liquid fraction distributions of PCMs were further affected.The effects of different dimensionless parameters(e.g.,tube-to-capsule diameter ratio,Reynolds number,and Stefan number)on the radial characteristics of HTF and PCMs were discussed.The results showed that different diameter ratios correspond to different radial porosity distributions.Further,with an increase in diameter ratio,HTF velocity varies significantly in the near wall region while the non-uniformity of HTF velocity in the center region will decrease.The Reynolds and Stefan numbers slightly impact the relative velocity distribution of the HTF-while higher Reynolds numbers can lead to a proportional improvement of velocity,an increase in Stefan number can promote heat storage of the packed bed LHS system.展开更多
Phase change absorbents for CO_(2)are of great interest because they are expected to greatly reduce the heat energy consumption during the regeneration process.Compared with other phase change absorbents,monoethanolam...Phase change absorbents for CO_(2)are of great interest because they are expected to greatly reduce the heat energy consumption during the regeneration process.Compared with other phase change absorbents,monoethanolamine(MEA)-sulfolane-water is inexpensive and has a fast absorption rate.It is one of the most promising solvents for large-scale industrial applications.Therefore,this study investigates the mass transfer performance of this phase change system in the process of CO_(2)absorption in a packed tower.By comparing the phase change absorbent and the ordinary absorbent,it is concluded that the use of MEA/sulfolane phase change absorbent has significantly improved mass transfer efficiency compared to a single MEA absorbent at the same concentration.In the 4 mol·L^(-1)MEA/5 mol·L^(-1)sulfolane system,the CO_(2)loading of the upper liquid phase after phase separation is almost zero,while the volume of the lower liquid phase sent to the desorption operation is about half of the total volume of the absorbent,which greatly reduces the energy consumption.This study also investigates the influence of operating parameters such as lean CO_(2)loading,gas and liquid flow rates,CO_(2)partial pressure,and temperature on the volumetric mass transfer coefficient(K_(G)α_(V)).The research shows that K_(G)α_(V) increases with increasing liquid flow rate and decreases with the increase of lean CO_(2)loading and CO_(2)partial pressure,while the inert gas flow rate and temperature have little effect on K_(G)α_(V).In addition,based on the principle of phase change absorption,a predictive equation for the K_(G)α_(V) of MEA-sulfolane in the packed tower was established.The K_(G)α_(V) obtained from the experiment is consistent with the model prediction,and the absolute average deviation(AAD)is 7.8%.展开更多
This study investigated catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-MnCu/γ-Al_(2)O_(3)(Cat)in a rotating packed bed(RPB)for the first time.The results showed that the value of the overal...This study investigated catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-MnCu/γ-Al_(2)O_(3)(Cat)in a rotating packed bed(RPB)for the first time.The results showed that the value of the overall decomposition rate constant of ozone(K_(c))and overall volumetric mass transfer coefficient(K_(L)a)are 4.28×10^(-3) s^(-1) and 11.60×10^(-3) s^(-1) respectively at an initial pH of 6,βof 40,Co3(g)of 60 mg·L^(-1)and Q_(L) of 85 L·h^(-1) in deionized water,respectively.Meanwhile,the K_(c) and K_(L)a values of Fenhe water are0.88×10^(-3) s^(-1) and 2.51×10^(-3) s^(-1) lower than deionized water,respectively.In addition,the K_(c) and K_(L)a values in deionized water for the Cat/O_(3)-RPB system are 44.86%and 47.41%higher than that for the Cat/O_(3)-BR(bubbling reactor)system,respectively,indicating that the high gravity technology can facilitate the decomposition and mass transfer of ozone in heterogeneous catalytic ozonation and provide some insights into the industrial wastewater.展开更多
We analyse the porous structure of the packed beds in the heat transfer test facility built for high temperature gas cooled reactors from several aspects,such as oscillatory porosity,average porosity,thickness effect,...We analyse the porous structure of the packed beds in the heat transfer test facility built for high temperature gas cooled reactors from several aspects,such as oscillatory porosity,average porosity,thickness effect,coordination number and contact angle.An understanding and comparison of the porous structure of the facility bed and the real reactor core are developed to make recommendations for the design and analysis of the heat transfer test facility.The results show that there is very little difference between the porous characteristics of the two packed beds of spheres.展开更多
A new mathematical model,designated as stochastic state pool model,is proposed for simulating the liquid flow andmass transfer behaviour,including the concentration profiles of liquid and gas phascs in a packed column...A new mathematical model,designated as stochastic state pool model,is proposed for simulating the liquid flow andmass transfer behaviour,including the concentration profiles of liquid and gas phascs in a packed column.Application ofthe new model is demonstrated by an example of the desorption of CO<sub>2</sub> in a packed column.展开更多
1 INTRODUCTIONA major problem in the design of packed columns is dimensioning the liquid distributor.Thenumber of outlets is an important factor,because it governs the quality of the liquiddistribution at the inlet cr...1 INTRODUCTIONA major problem in the design of packed columns is dimensioning the liquid distributor.Thenumber of outlets is an important factor,because it governs the quality of the liquiddistribution at the inlet cross-section and thus the extent to which the packing is Wetted.Thehigher the degree of wetting and thus the greater the area of phase contact,the more efficientthe mass and heat transfer within the bed of packing.展开更多
The rotating packed bed(RPB)has been widely used in gas-liquid flow systems as a process intensification device,exhibiting excellent mass transfer enhancement characteristics.However,the complex internal structure and...The rotating packed bed(RPB)has been widely used in gas-liquid flow systems as a process intensification device,exhibiting excellent mass transfer enhancement characteristics.However,the complex internal structure and the high-speed rotation of the rotor in RPB bring significant challenges to study the intensification mechanism by experiment methods.In the past two decades,Computational fluid dynamics(CFD)has been gradually applied to simulate the hydrodynamics and mass transfer characteristics in RPB and instruct the reactor design.This article covers the development of the CFD simulation of gasliquid flow in RPB.Firstly,the improvement of the simulation method in the aspect of mathematical models,geometric models,and solving methods is introduced.Secondly,new progress of CFD simulation about hydrodynamic and mass transfer characteristics in RPB is reviewed,including pressure drop,velocity distribution,flow pattern,and concentration distribution,etc.Some new phenomena such as the end effect area with the maximum turbulent have been revealed by this works.In addition,the exploration of developing new reactor structures by CFD simulation is introduced and it is proved that such new structures are competitive to different applications.The defects of current research and future development directions are also discussed at last.展开更多
Rotating packed bed has high efficiency of gas-liquid mass transfer.So it is significant to investigate fluid motion in rotating packed bed.Numerical simulations of the effects of packing feature size on liquid flow c...Rotating packed bed has high efficiency of gas-liquid mass transfer.So it is significant to investigate fluid motion in rotating packed bed.Numerical simulations of the effects of packing feature size on liquid flow characteristics in a rotating packed bed are reported in this paper.The particle image velocimetry is compared with the numerical simulations to validate the turbulent model.Results show that the liquid exists in the packing zone in the form of droplet and liquid line,and the cavity is droplet.When the radial thickness of the packing is less than 0.101 m,liquid line and droplets appear in the cavity.When rotational speed and radial thickness of the packing increase,the average diameter of the droplets becomes smaller,and the droplet size distribution becomes uniform.As the initial velocity of the liquid increases,the average droplet diameter increases and the uniformity of particle size distribution become worse.The droplet velocity increases with the radial thickness of the packing increasing,and gradually decreases when it reaches the cavity region.The effect of packing thickness is most substantial through linear fitting.The predicted and simulated values are within±15%.The cumulative volume distribution curves of the experimental and simulated droplets are consistent with the R-R distribution.展开更多
A rotating packed bed(RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor ...A rotating packed bed(RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient(kLS) have been investigated. The correlation for predicting kLSwas proposed, and the deviation between the experimental and predicted values was within±12%. The liquid–solid volumetric mass transfer coefficient(kLSaLS) ranged from 0.04–0.14 1^-1, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.展开更多
The rotating packed bed(RPB), mainly including the countercurrent-flow RPB(Counter-RPB) and the crosscurrentflow RPB(Cross-RPB) that are classified from the perspective of gas-liquid contact style, is a novel process ...The rotating packed bed(RPB), mainly including the countercurrent-flow RPB(Counter-RPB) and the crosscurrentflow RPB(Cross-RPB) that are classified from the perspective of gas-liquid contact style, is a novel process intensification device. A significant measurement standard for evaluating the performance of RPB is the mass transfer effect. In order to compare the mass transfer characteristics of Counter-RPB and Cross-RPB with the same size, the liquid volumetric mass transfer coefficient(k_La_e) and effective interfacial area(a_e) were measured under identical operating conditions. Meanwhile, the comparison of comprehensive mass transfer performance was conducted using the ratio of ΔP(pressure drop) to kLae as the standard. Experimental results indicated that kLae and ae increased with the increase in liquid spray density q, gas velocity u, and high gravity factor β. Furthermore, compared with the Cross-RPB, the Counter-RPB has higher liquid volumetric mass transfer coefficient and slightly larger effective interfacial area. The experimental results of comprehensive mass transfer performance showed that the Counter-RPB had higher ΔP/k_La_e than the Cross-RPB with changes in liquid spray density and high gravity factor, and there exists a turning point at 0.71 m/s accompanied by a variation with gas velocity. Moreover, the relative error of experimental value to calculated value, which was computed by the correlative expressions of kLae, was less than 5 %. In conclusion, the mass transfer characteristics of RPB are deeply impacted by the manner in which the flows are established and the Cross-RPB would have a great potential for industrial scale-up applications.展开更多
AIM To determine if packed red blood cell transfusions contribute to the development of parenteral nutrition associated liver disease. METHODS A retrospective chart review of 49 premature infants on parenteral nutriti...AIM To determine if packed red blood cell transfusions contribute to the development of parenteral nutrition associated liver disease. METHODS A retrospective chart review of 49 premature infants on parenteral nutrition for > 30 d who received packed red blood cell(PRBC) transfusions was performed. Parenteral nutrition associated liver disease was primarily defined by direct bilirubin(db) > 2.0 mg/dL. A high transfusion cohort was defined as receiving > 75 mL packed red blood cells(the median value). KaplanMeier plots estimated the median volume of packedred blood cells received in order to develop parenteral nutrition associated liver disease.RESULTS Parenteral nutritional associated liver disease(PNALD) was noted in 21(43%) infants based on db. Among the 27 high transfusion infants, PNALD was present in 17(64%) based on elevated direct bilirubin which was significantly greater than the low transfusion recipients. About 50% of the infants, who were transfused 101-125 mL packed red blood cells, developed PNALD based on elevation of direct bilirubin. All infants who were transfused more than 200 mL of packed red blood cells developed PNALD. Similar results were seen when using elevation of aspartate transaminase or alanine transaminase to define PNALD.CONCLUSION In this retrospective, pilot study there was a statistically significant correlation between the volume of PRBC transfusions received by premature infants and the development of PNALD.展开更多
<strong>Introduction:</strong> <span style="font-family:Verdana;">Packed cell transfusion is a lifesaving procedure in premature babies as they have more complications as compared to babies...<strong>Introduction:</strong> <span style="font-family:Verdana;">Packed cell transfusion is a lifesaving procedure in premature babies as they have more complications as compared to babies who are born at term. Complications related to prematurity increase as gestational age decreases and anemia is one of the complications of prematurity which needs packed cell transfusions. To date, when to transfuse preterm babies and what would be the threshold for hemoglobin and hematocrit is still a point of argument as well as liberal versus restrictive transfusion protocols have been developed but what should be followed still needs more data. In our study, we have observed frequencies of different indications of packed cell transfusion in the neonatal intensive care unit of a tertiary care hospital. This endeavor will help in the establishment of guidelines regarding transfusion and the threshold on which any intervention should be done also it would be a step towards the identification of preventable causes that lead to transfusion and transfusion-related risks and hazards.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Objective:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">To determine the indication of packed cell transfusion and their frequencies in preterm neonates.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Study Design:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">This was a cross-sectional study.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Setting:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">The study was carried out in the neonatal intensive care unit (NICU).</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Study Duration:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">The duration of the study was 1 year.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Material and Methods:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">A total of 246 preterm neonates admitted to Aga Khan University Hospital (AKUH) neonatal intensive care unit in the tenure of 1 year, fulfilling the inclusion criteria and requiring packed cell transfusion were included. After the approval from ethical review committee, charts were reviewed for gestational age, birth weight, mode of delivery (normal vaginal or Cesarean-section) were recorded. Indications of packed cell transfusion (intraventricular hemorrhage, infection or sepsis, anemia of prematurity, phlebotomy losses, increase oxygen requirement, hematological causes, other causes of hemorrhage and other causes) were observed and recorded. Pre-transfusion hemoglobin levels (g/dL) and hematocrit levels were also recorded. Other information like number and volume of transfusion and day of life on which transfusion was administered was also documented.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Results:</span></b><b><span style="font-family:""> </span></b><span style="font-family:""><span style="font-family:Verdana;">A total of 246 critically ill children were enrolled in this study. Of t</span><span style="font-family:Verdana;">he total, 52.8% were baby boys and 47.2% were baby girls. 57% of babies were born via cesarean section and 43% were born via vaginal delivery. Out of total preterm newborns admitted in NICU, 22.8% were extremely preterm, 35.4% were very preterm and 41.9% were late preterm. Mean gestational age was observed to be 31 (±4) weeks and the mean birth weight of newborns was 1500 (±600) grams.</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">Indications of packed cell transfusion observed in our study are intraventricular hemorrhage 10%, 26% sepsis/infection</span><span style="font-family:Verdana;">, 4% hematological disorders, 12.8% anemia of prematurity, 25.2% was related to increase in oxygen requirement, 13% other hematological causes and 9.3% other causes.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Conclusion:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">An increase in oxygen requirement and anemia of prematurity were the indications that were observed in the extremely preterm and very preterm groups. Sepsis and increase oxygen requirement are some of the major causes of transfusions observed in the late preterm group. Preventable indications can be one of the areas that can be worked on and will reduce the need for transfusion in preterm babies with subsequent prevention of transfusion-associated risks.</span>展开更多
Correlations will be presented to describe liquid hold up, loading and flooding capacity, volumetric mass transfer coefficients on liquid and gas or vapour phase and the pressure drop as a basis for computing packed c...Correlations will be presented to describe liquid hold up, loading and flooding capacity, volumetric mass transfer coefficients on liquid and gas or vapour phase and the pressure drop as a basis for computing packed columns, dumped and regular as well, including the influence of end effects on scaling. The relationships are found on a sound physical and mathematical basis and their validity were confirmed by experimental investigations of many packings; some of them were selected to be considered in this work.展开更多
Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhes...Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhesion solid bodies. The packed volume and the void ratio of a large number of randomly packed RBCs are clari?ed,and the effects of the RBC shape, the mesh size, the cell number, and the container size are investigated. The results show that the packed human RBCs with normal shape have a void ratio of 28.45%, which is slightly higher than that of the ?at or thick cells used in this study. Such information is bene?cial to the further understanding on the geometric features of human RBCs and the research on RBC simulations.展开更多
基金the support from the National Natural Science Foundation of China (22008157,21978178)。
文摘Rotating packed bed(RPB) is one of the most effective gas–liquid mass transfer enhancement reactors, its effective specific mass transfer area(ae) is critical to understand the mass transfer process. By using the NaOH–CO_(2) chemical absorption method, the aevalues of three RPB reactors with different rotor sizes were measured under different operation conditions. The results showed that the high gravity factor and liquid flow rate were major affecting factors, while the gas flow rate exhibited minor influence.The radius of packing is the dominant equipment factor to affect aevalue. The results indicated that the contact area depends on the dispersion of the liquid phase, thus the centrifugal force of rotating packed bed greatly influenced the aevalue. Moreover, the measured ae/ap(effective specific mass transfer area/specific surface area of packing) values were fitted with dimensionless correlation formulas. The unified correlation formula with dimensionless bed size parameter can well predict the experimental data and the prediction errors were within 15%.
文摘Thermal Energy Storage is becoming a necessary component of sustainable energy production systems as it helps alleviate intrinsic limitations of Renewable Energy Sources, such as intermittent use and mismatch between power demand and supply. This paper discusses a packed bed thermocline tank as a thermal energy storage solution. Firstly, this paper presents the development of a numerical model calculating heat transfers within the tank, based on a discretization over several nodes and the nodal formulation of the heat balance equation. The model considers a filler material and a heat transferring fluid and uses the finite difference method to calculate the temperature evolution of the two media across the tank. The model was validated with two different packed bed systems from the literature during a discharging process, presenting a good fit with the experimental results. Secondly, the experimental packed bed is presented and characterized for a charging cycle from ambient temperature to approximately 180?C. The charging experiment was accurately reproduced with the numerical model requiring minimal computational time. Two additional charging modes were simulated with different inlet HTF conditions: constant temperature and varying temperature following the profile produced by a thermal solar collector field. The temperature profiles obtained from the three charging modes were analysed and compared to each other. The proposed numerical and experimental tools will be used in future studies for a better understanding of the design and operating conditions of packed bed thermal energy storage systems.
基金Supported by the National Key Research and Development Program(2016YFB0301702)National Natural Science Foundation of China(21490584,21878298,91534105)+2 种基金Major National Scientific Instrument and Equipment Development Project(21427814)Key Research Program of Frontier Sciences of CAS(QYZDJ-SSW-JSC030)Jiangsu National Synergetic Innovation Center for Advanced Materials.
文摘The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios(N = D/d b 8) where the local phenomena of channeling near the wall and backflow in the bed are dominant. The recent"solid particle" meshing method is too complicated for mesh generation, especially for non-spherical particles in large random packed beds, which seriously hinders its development. In this work, a novel high-fidelity mesh model is proposed for simulation of fixed bed reactors by combining the immersed boundary and adaptive meshing methods. This method is suitable for different shapes of particles, which ingeniously avoids handling the complex "contact point" problem. Several packed beds with two different shapes of particles are investigated with this model, and the local flow in the bed is simulated without geometrical simplification. The predicted pressure drop across the fixed bed and heat transfer of the single particle are in good agreement with the corresponding empirical relations. Compared with spherical particles, the packed bed packing with pentaphyllous particles has lower pressure drop and better heat/mass transfer performance, and it shows that this method can be used for the screening of particle shapes in a fixed bed.
基金financially supported by the Natural Science Foundations of China(No.21206153,21376229)the Excellent Youth Science and Technology Foundation of Province Shanxi of China(No.2014021007)+1 种基金the Natural Science Foundation of Shanxi Province(Grant No.2011021012,2012011008-2)the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi(201316)
文摘Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.
基金This work is supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(51521004)the National Natural Science Foundation of China(51906150).
文摘Owing to its high heat storage capacity and fast heat transfer rate,packed bed latent heat storage(LHS)is considered as a promising method to store thermal energy.In a packed bed,the wall effect can impact the packing arrangement of phase change material(PCM)capsules,inducing radial porosity oscillation.In this study,an actual-arrangement-based three-dimensional packed bed LHS model was built to consider the radial porosity oscillation.Its fluid flow and heat transfer were analyzed.With different cylindrical sub-surfaces intercepted along the radial direction in the packed bed,the corresponding relationships between the arrangement of capsules and porosity oscillation were identified.The oscillating distribution of radial porosity led to a non-uniform distribution of heat transfer fluid(HTF)velocity.As a result,radial temperature distributions and liquid fraction distributions of PCMs were further affected.The effects of different dimensionless parameters(e.g.,tube-to-capsule diameter ratio,Reynolds number,and Stefan number)on the radial characteristics of HTF and PCMs were discussed.The results showed that different diameter ratios correspond to different radial porosity distributions.Further,with an increase in diameter ratio,HTF velocity varies significantly in the near wall region while the non-uniformity of HTF velocity in the center region will decrease.The Reynolds and Stefan numbers slightly impact the relative velocity distribution of the HTF-while higher Reynolds numbers can lead to a proportional improvement of velocity,an increase in Stefan number can promote heat storage of the packed bed LHS system.
基金The National Natural Science Foundation of China(NSFC-Nos.22138002,22078083,and 21978075)the Hunan Key R&D Program Project(2020NK2015)+2 种基金National Key R&D Projects in Changsha(kh2005018)National Key Research&Development Program-Intergovernmental International Science and Technology Innovation Cooperation Project(2021YFE0112800)the science and technology innovation Program of Hunan Province(2020RC5032)。
文摘Phase change absorbents for CO_(2)are of great interest because they are expected to greatly reduce the heat energy consumption during the regeneration process.Compared with other phase change absorbents,monoethanolamine(MEA)-sulfolane-water is inexpensive and has a fast absorption rate.It is one of the most promising solvents for large-scale industrial applications.Therefore,this study investigates the mass transfer performance of this phase change system in the process of CO_(2)absorption in a packed tower.By comparing the phase change absorbent and the ordinary absorbent,it is concluded that the use of MEA/sulfolane phase change absorbent has significantly improved mass transfer efficiency compared to a single MEA absorbent at the same concentration.In the 4 mol·L^(-1)MEA/5 mol·L^(-1)sulfolane system,the CO_(2)loading of the upper liquid phase after phase separation is almost zero,while the volume of the lower liquid phase sent to the desorption operation is about half of the total volume of the absorbent,which greatly reduces the energy consumption.This study also investigates the influence of operating parameters such as lean CO_(2)loading,gas and liquid flow rates,CO_(2)partial pressure,and temperature on the volumetric mass transfer coefficient(K_(G)α_(V)).The research shows that K_(G)α_(V) increases with increasing liquid flow rate and decreases with the increase of lean CO_(2)loading and CO_(2)partial pressure,while the inert gas flow rate and temperature have little effect on K_(G)α_(V).In addition,based on the principle of phase change absorption,a predictive equation for the K_(G)α_(V) of MEA-sulfolane in the packed tower was established.The K_(G)α_(V) obtained from the experiment is consistent with the model prediction,and the absolute average deviation(AAD)is 7.8%.
基金supported by the Specialized Research Fund for Sanjin Scholars Program of Shanxi Province(201707)Key Research&Development Plan of Shanxi Province(201903D321059)+2 种基金Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province(20200004)Transformation and Cultivation Projects of Scientific and Technological Achievements in Universities of Shanxi Province Institutions(2020CG040)the China National Key Project of Science and Technology “Major Science and Technology Program for Water Pollution Control and Treatment”(2018ZX07601001)。
文摘This study investigated catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-MnCu/γ-Al_(2)O_(3)(Cat)in a rotating packed bed(RPB)for the first time.The results showed that the value of the overall decomposition rate constant of ozone(K_(c))and overall volumetric mass transfer coefficient(K_(L)a)are 4.28×10^(-3) s^(-1) and 11.60×10^(-3) s^(-1) respectively at an initial pH of 6,βof 40,Co3(g)of 60 mg·L^(-1)and Q_(L) of 85 L·h^(-1) in deionized water,respectively.Meanwhile,the K_(c) and K_(L)a values of Fenhe water are0.88×10^(-3) s^(-1) and 2.51×10^(-3) s^(-1) lower than deionized water,respectively.In addition,the K_(c) and K_(L)a values in deionized water for the Cat/O_(3)-RPB system are 44.86%and 47.41%higher than that for the Cat/O_(3)-BR(bubbling reactor)system,respectively,indicating that the high gravity technology can facilitate the decomposition and mass transfer of ozone in heterogeneous catalytic ozonation and provide some insights into the industrial wastewater.
基金Supported by the National Science and Technology Major Project under Grant No ZX06901the National Natural Science Foundation of China under Grant No 11072131.
文摘We analyse the porous structure of the packed beds in the heat transfer test facility built for high temperature gas cooled reactors from several aspects,such as oscillatory porosity,average porosity,thickness effect,coordination number and contact angle.An understanding and comparison of the porous structure of the facility bed and the real reactor core are developed to make recommendations for the design and analysis of the heat transfer test facility.The results show that there is very little difference between the porous characteristics of the two packed beds of spheres.
文摘A new mathematical model,designated as stochastic state pool model,is proposed for simulating the liquid flow andmass transfer behaviour,including the concentration profiles of liquid and gas phascs in a packed column.Application ofthe new model is demonstrated by an example of the desorption of CO<sub>2</sub> in a packed column.
文摘1 INTRODUCTIONA major problem in the design of packed columns is dimensioning the liquid distributor.Thenumber of outlets is an important factor,because it governs the quality of the liquiddistribution at the inlet cross-section and thus the extent to which the packing is Wetted.Thehigher the degree of wetting and thus the greater the area of phase contact,the more efficientthe mass and heat transfer within the bed of packing.
基金supported by the National Natural Science Foundation of China(21978011 and 21725601).
文摘The rotating packed bed(RPB)has been widely used in gas-liquid flow systems as a process intensification device,exhibiting excellent mass transfer enhancement characteristics.However,the complex internal structure and the high-speed rotation of the rotor in RPB bring significant challenges to study the intensification mechanism by experiment methods.In the past two decades,Computational fluid dynamics(CFD)has been gradually applied to simulate the hydrodynamics and mass transfer characteristics in RPB and instruct the reactor design.This article covers the development of the CFD simulation of gasliquid flow in RPB.Firstly,the improvement of the simulation method in the aspect of mathematical models,geometric models,and solving methods is introduced.Secondly,new progress of CFD simulation about hydrodynamic and mass transfer characteristics in RPB is reviewed,including pressure drop,velocity distribution,flow pattern,and concentration distribution,etc.Some new phenomena such as the end effect area with the maximum turbulent have been revealed by this works.In addition,the exploration of developing new reactor structures by CFD simulation is introduced and it is proved that such new structures are competitive to different applications.The defects of current research and future development directions are also discussed at last.
基金supported by the Key Research&Development Plan of Shanxi Province(201903D321059)Shanxi Scholarship Council of China(HGKY2019071)。
文摘Rotating packed bed has high efficiency of gas-liquid mass transfer.So it is significant to investigate fluid motion in rotating packed bed.Numerical simulations of the effects of packing feature size on liquid flow characteristics in a rotating packed bed are reported in this paper.The particle image velocimetry is compared with the numerical simulations to validate the turbulent model.Results show that the liquid exists in the packing zone in the form of droplet and liquid line,and the cavity is droplet.When the radial thickness of the packing is less than 0.101 m,liquid line and droplets appear in the cavity.When rotational speed and radial thickness of the packing increase,the average diameter of the droplets becomes smaller,and the droplet size distribution becomes uniform.As the initial velocity of the liquid increases,the average droplet diameter increases and the uniformity of particle size distribution become worse.The droplet velocity increases with the radial thickness of the packing increasing,and gradually decreases when it reaches the cavity region.The effect of packing thickness is most substantial through linear fitting.The predicted and simulated values are within±15%.The cumulative volume distribution curves of the experimental and simulated droplets are consistent with the R-R distribution.
基金supported by the National Natural Science Foundation of China(Nos.21676009 and 21725601)。
文摘A rotating packed bed(RPB) reactor has substantially potential for the process intensification of heterogeneous catalytic reactions. However, the scarce knowledge of the liquid–solid mass transfer in the RPB reactor is a barrier for its design and scale-up. In this work, the liquid–solid mass transfer in a RPB reactor installed with structured foam packing was experimentally studied using copper dissolution by potassium dichromate. Effects of rotational speed, liquid and gas volumetric flow rate on the liquid–solid mass transfer coefficient(kLS) have been investigated. The correlation for predicting kLSwas proposed, and the deviation between the experimental and predicted values was within±12%. The liquid–solid volumetric mass transfer coefficient(kLSaLS) ranged from 0.04–0.14 1^-1, which was approximately 5 times larger than that in the packed bed reactor. This work lays the foundation for modeling of the RPB reactor packed with structured foam packing for heterogeneous catalytic reaction.
基金supported by the National Key R&D Program of China:The ultra-low emission control technology for coal-fired industrial boilers(2016YFC0204103)the Provincial Key R&D Program of Shanxi:R&D of the coal-fired industrial boiler smoke ultra-low emission technology and equipment(201703D111018)
文摘The rotating packed bed(RPB), mainly including the countercurrent-flow RPB(Counter-RPB) and the crosscurrentflow RPB(Cross-RPB) that are classified from the perspective of gas-liquid contact style, is a novel process intensification device. A significant measurement standard for evaluating the performance of RPB is the mass transfer effect. In order to compare the mass transfer characteristics of Counter-RPB and Cross-RPB with the same size, the liquid volumetric mass transfer coefficient(k_La_e) and effective interfacial area(a_e) were measured under identical operating conditions. Meanwhile, the comparison of comprehensive mass transfer performance was conducted using the ratio of ΔP(pressure drop) to kLae as the standard. Experimental results indicated that kLae and ae increased with the increase in liquid spray density q, gas velocity u, and high gravity factor β. Furthermore, compared with the Cross-RPB, the Counter-RPB has higher liquid volumetric mass transfer coefficient and slightly larger effective interfacial area. The experimental results of comprehensive mass transfer performance showed that the Counter-RPB had higher ΔP/k_La_e than the Cross-RPB with changes in liquid spray density and high gravity factor, and there exists a turning point at 0.71 m/s accompanied by a variation with gas velocity. Moreover, the relative error of experimental value to calculated value, which was computed by the correlative expressions of kLae, was less than 5 %. In conclusion, the mass transfer characteristics of RPB are deeply impacted by the manner in which the flows are established and the Cross-RPB would have a great potential for industrial scale-up applications.
文摘AIM To determine if packed red blood cell transfusions contribute to the development of parenteral nutrition associated liver disease. METHODS A retrospective chart review of 49 premature infants on parenteral nutrition for > 30 d who received packed red blood cell(PRBC) transfusions was performed. Parenteral nutrition associated liver disease was primarily defined by direct bilirubin(db) > 2.0 mg/dL. A high transfusion cohort was defined as receiving > 75 mL packed red blood cells(the median value). KaplanMeier plots estimated the median volume of packedred blood cells received in order to develop parenteral nutrition associated liver disease.RESULTS Parenteral nutritional associated liver disease(PNALD) was noted in 21(43%) infants based on db. Among the 27 high transfusion infants, PNALD was present in 17(64%) based on elevated direct bilirubin which was significantly greater than the low transfusion recipients. About 50% of the infants, who were transfused 101-125 mL packed red blood cells, developed PNALD based on elevation of direct bilirubin. All infants who were transfused more than 200 mL of packed red blood cells developed PNALD. Similar results were seen when using elevation of aspartate transaminase or alanine transaminase to define PNALD.CONCLUSION In this retrospective, pilot study there was a statistically significant correlation between the volume of PRBC transfusions received by premature infants and the development of PNALD.
文摘<strong>Introduction:</strong> <span style="font-family:Verdana;">Packed cell transfusion is a lifesaving procedure in premature babies as they have more complications as compared to babies who are born at term. Complications related to prematurity increase as gestational age decreases and anemia is one of the complications of prematurity which needs packed cell transfusions. To date, when to transfuse preterm babies and what would be the threshold for hemoglobin and hematocrit is still a point of argument as well as liberal versus restrictive transfusion protocols have been developed but what should be followed still needs more data. In our study, we have observed frequencies of different indications of packed cell transfusion in the neonatal intensive care unit of a tertiary care hospital. This endeavor will help in the establishment of guidelines regarding transfusion and the threshold on which any intervention should be done also it would be a step towards the identification of preventable causes that lead to transfusion and transfusion-related risks and hazards.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Objective:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">To determine the indication of packed cell transfusion and their frequencies in preterm neonates.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Study Design:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">This was a cross-sectional study.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Setting:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">The study was carried out in the neonatal intensive care unit (NICU).</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Study Duration:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">The duration of the study was 1 year.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Material and Methods:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">A total of 246 preterm neonates admitted to Aga Khan University Hospital (AKUH) neonatal intensive care unit in the tenure of 1 year, fulfilling the inclusion criteria and requiring packed cell transfusion were included. After the approval from ethical review committee, charts were reviewed for gestational age, birth weight, mode of delivery (normal vaginal or Cesarean-section) were recorded. Indications of packed cell transfusion (intraventricular hemorrhage, infection or sepsis, anemia of prematurity, phlebotomy losses, increase oxygen requirement, hematological causes, other causes of hemorrhage and other causes) were observed and recorded. Pre-transfusion hemoglobin levels (g/dL) and hematocrit levels were also recorded. Other information like number and volume of transfusion and day of life on which transfusion was administered was also documented.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Results:</span></b><b><span style="font-family:""> </span></b><span style="font-family:""><span style="font-family:Verdana;">A total of 246 critically ill children were enrolled in this study. Of t</span><span style="font-family:Verdana;">he total, 52.8% were baby boys and 47.2% were baby girls. 57% of babies were born via cesarean section and 43% were born via vaginal delivery. Out of total preterm newborns admitted in NICU, 22.8% were extremely preterm, 35.4% were very preterm and 41.9% were late preterm. Mean gestational age was observed to be 31 (±4) weeks and the mean birth weight of newborns was 1500 (±600) grams.</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">Indications of packed cell transfusion observed in our study are intraventricular hemorrhage 10%, 26% sepsis/infection</span><span style="font-family:Verdana;">, 4% hematological disorders, 12.8% anemia of prematurity, 25.2% was related to increase in oxygen requirement, 13% other hematological causes and 9.3% other causes.</span><span style="font-family:""> </span><b><span style="font-family:Verdana;">Conclusion:</span></b><b><span style="font-family:""> </span></b><span style="font-family:Verdana;">An increase in oxygen requirement and anemia of prematurity were the indications that were observed in the extremely preterm and very preterm groups. Sepsis and increase oxygen requirement are some of the major causes of transfusions observed in the late preterm group. Preventable indications can be one of the areas that can be worked on and will reduce the need for transfusion in preterm babies with subsequent prevention of transfusion-associated risks.</span>
文摘Correlations will be presented to describe liquid hold up, loading and flooding capacity, volumetric mass transfer coefficients on liquid and gas or vapour phase and the pressure drop as a basis for computing packed columns, dumped and regular as well, including the influence of end effects on scaling. The relationships are found on a sound physical and mathematical basis and their validity were confirmed by experimental investigations of many packings; some of them were selected to be considered in this work.
基金Project supported by the Engineering and Physical Sciences Research Council(EPSRC)Turbulence Consortium Grant(No.EP/G069581/1)the Marie Curie International Incoming Fellowship(No.PIIF-GA-253453)
文摘Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhesion solid bodies. The packed volume and the void ratio of a large number of randomly packed RBCs are clari?ed,and the effects of the RBC shape, the mesh size, the cell number, and the container size are investigated. The results show that the packed human RBCs with normal shape have a void ratio of 28.45%, which is slightly higher than that of the ?at or thick cells used in this study. Such information is bene?cial to the further understanding on the geometric features of human RBCs and the research on RBC simulations.
