Large vertical pipes are key structures connecting subsea wells to offshore ***,existing studies mainly focus on small vertical *** a vertical acrylic pipe with 80 mm inner diameter and 1. m height,a high-speed camera...
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Large vertical pipes are key structures connecting subsea wells to offshore ***,existing studies mainly focus on small vertical *** a vertical acrylic pipe with 80 mm inner diameter and 1. m height,a high-speed camera was used to visually research the influences of pipe diameters,liquid properties and inlet effect on air-water co-{1. *** {1. regime maps of vertical pipes(diameters are in the range of 50e1.9 mm)were compared and the critical gas velocity of the transition boundary from bubble to slug {1. tended to increase with the increase of diameters at D≥80 ***-flux models were established in different {1. regimes and liquid properties have a significant effect on drift coefficients of bubble {1. and slug {1.(void fraction a≤0.4).The influence of inlet turbulent effect on the gas-liquid interface distribution gradually weakened and disappeared from the pipe base to 85D,where the {1. was fully *** frequency has a trend of increase first and then decrease with the gas Weber numbers increasing at low liquid superficial velocities(J_(L)≤0.31.m/s).And on the basis of this law,a new slug frequency correlation was *** was found that there was an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction.
Bubbles formed during chemical processes in fluidized beds govern the bed hydrodynamics and opera-tional efficiency, thereby having a significant impact on their design and scale-up. In this study, a two-fluid model w...
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Bubbles formed during chemical processes in fluidized beds govern the bed hydrodynamics and opera-tional efficiency, thereby having a significant impact on their design and scale-up. In this study, a two-fluid model was used to simulate the bubble behavior in a quasi-two-dimensional fluidized bed within the bubble-based energy minimization multiscale (EMMS) approach. We performed experiments to verify the model and proposed a correlation of the heterogeneous index for various parameters to calculate the coefficient of drag for the bubble-based EMMS model. Moreover, the simulation results obtained from the homogeneous drag models and EMMS bubbling model were compared with experimental data and empirical correlations. The simulation results of the EMMS approach showed good agreement with the experimental data in the distribution of the vertical bubble velocity with chord length. Compared with the results from the homogeneous models, the distributions of vertical velocity and diameter of the bubbles predicted by the EMMS-bubbling model were in better agreement with empirical correlations. Moreover, the frequency distributions of bubble properties including bubble diameter, aspect ratio, and shape factor for different gas-inlet velocities were obtained.
A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyc...
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A new concept of a supercritical water （SCW） circulating fiuidized bed reactor is proposed to produce hydrogen from coal/biomass gasification. The cyclone is a key component of the reactor system, in this paper, cyclones with a single circular inlet （SCI） or a double circular inlet （DCI） were designed to adapt to the supercritical conditions. We evaluated the separation performance of the two cyclones using numerical simulations. A three-dimensional Reynolds stress model was used to simulate the turbulent {1. of the fluid, and a stochastic Lagrangian model was used to simulate the particle motion. The {1. fields of both cyclones were three-dimensionally unsteady and similar to those of traditional gas-solid cyclones. Secondary circulation phenomena were discovered and their influence on particle separation was estimated. Analyzing the distribution of the turbulence kinetic energy revealed that the most intensive turbulence existed in the zone near the vortex finder while the {1. in the central part was relatively stable. The particle concentration distribution was non-uniform because of centrifugal forces. The distribution area can be divided into three parts according to the motion of the particles. In addition, the separation efficiency of both cyclones increased with the inlet SCaN velocity. Because of its perturbance {1., the DCI separator had higher separation efficiency than the SCI separator under comparable simulations. However, this was at the expense of a higher pressure drop across the cyclone.
As a benign energy vector,hydrogen has been discussed for a long *** water gasification was one of good ways to produce ***,supercritical water gasification system with H_(2)O transporting was energy consuming in the ...
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As a benign energy vector,hydrogen has been discussed for a long *** water gasification was one of good ways to produce ***,supercritical water gasification system with H_(2)O transporting was energy consuming in the process of heating due to the high specific heat of H_(2)O.A new supercritical water gasification system was established in this paper with supercritical CO_(2)as medium *** plastics were used as the sample transported by CO_(2).Production yields,energy flow and exergy flow of the system were collected and the influence of temperature,pressure,gasification concentration and transporting concentration was *** flow of H_(2)O input into the reactor was 1.00 kg/*** typical condition was as follow:temperature 923.1. K,pressure 23 MPa,and the mass ratio of water,sample and transporting medium was 1.0:9:*** of H_(2),CH4,CO and CO_(2)at this condition was 8.1.kg/h,39.6 kg/h,6.6 kg/h and 1.7.5 kg/h,*** system with H_(2)O transporting was used to compare with the supercritical CO_(2)transporting system and proved that system with CO_(2)transporting could reduce the loss of both energy and exergy while the reduce of each gas production yield was less than 0.1.mol/mol.
Recently,plasma-assisted combustion has become a potentially applicable technology in many combustion *** this paper,a dielectric barrier discharge（DBD） plasma generator is designed to explore the effect of plasma o...
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Recently,plasma-assisted combustion has become a potentially applicable technology in many combustion *** this paper,a dielectric barrier discharge（DBD） plasma generator is designed to explore the effect of plasma on the CH4 oxidation process,and several properties of combustion are ***,in the presence or absence of plasma discharge,physical appearance of the flame is examined and ***,the flame propagation velocity is calculated by the flame front extracted from the imaging data with the Bunsen burner ***,the main molecular components and their intensity variation in the flame and the plasma zones are identified with an emission spectrograph to analyze the effect of active species on the combustion *** also discuss the possible kinetic regime of plasma-assisted *** results imply that plasma discharge applied to the premixed CH_4/O_2/He mixture significantly raises the flame speed with equivalence ratios ranging from 0.85 to 1.1.,with the flame speed improved by 1.%to 35%.It can be seen that plasma can improve methane oxidation efficiency in the premixed fuel/oxidizer,especially at a low equivalence ratio.
A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dime...
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A computational particle fluid-dynamics model coupled with an energy-minimization multi-scale(EMMS)drag model was applied to investigate the influence of particle-size distribution on the hydrodynamics of a three-dimensional full-loop circulating fluidized *** particle systems,including one monodisperse and two polydisperse cases,were *** numerical model was validated by comparing its results with the experimental axial voidage distribution and solid mass *** EMMS drag model had a high accuracy in the computational particle fluid-dynamics simulation of the three-dimensional full-loop circulating fluidized *** total number of parcels in the system(Np)influenced the axial voidage distribution in the riser,especially at the lower part of the *** numerical simulation results showed that axial segregation by size was predicted in the two polydisperse cases and the segregation size increased with an increase in the number of size *** axial voidage distribution at the lower portion of the riser was significantly influenced by particle-size ***,radial segregation could only be correctly predicted in the upper region of the riser in the polydisperse case of three solid species.
Supercritical water(SCW)fluidized bed reactors convert biomass to fuels without pollutants *** this work,experimental studies were carried out to investigate voidage distribution in an SCW fu-idized bed by capacitance...
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Supercritical water(SCW)fluidized bed reactors convert biomass to fuels without pollutants *** this work,experimental studies were carried out to investigate voidage distribution in an SCW fu-idized bed by capacitance *** sands with different particle sizes were fluidized by SCW under system pressure of 20-27 MPa and temperature of 41.-570℃.The effect of operation conditions on voidage distributions of the emulsion phase(*** voidage and probability density)is discussed.A predicting correlation between voidage and superficial velocity in emulsion phase is *** relative error of the correlation is within+25%.These research results provide useful guidance for the optimization of supercritical water gasification technology.
Characterisations of instantaneous mixing behaviours in fluidised beds with binary mixtures has many *** studied the instantaneous mixing characteristics of binary mixtures in a 2-D quasi gas-solid fluidised bed using...
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Characterisations of instantaneous mixing behaviours in fluidised beds with binary mixtures has many *** studied the instantaneous mixing characteristics of binary mixtures in a 2-D quasi gas-solid fluidised bed using a capacitance probe *** method enabled the quantitative assessment of instantaneous mixing behaviours,including mixing index,rate,and *** kinds of binary mixtures of similar size but different density were used for the transient and steady fluidisation experiments in a bubbling fluidised *** mixing curves of initially segregated binary mixtures were acquired,and the instantaneous characteristics for the entire process were *** equation was proposed to describe the mixing process and predict the mixing degree over *** comparing experiments with different working conditions,the effects of superficial gas velocity and density ratio on the mixing in the centre and at the wall of the fluidised bed were *** the stable fluidisation stage,the axial concentration profiles of the mixtures were obtained,and the mechanisms of mixing were *** showed that the mixing level increased logarithmically with time and eventually reached a relatively stable *** the superficial gas velocity and reducing the density ratio promoted mixing and reduced mixing *** superficial gas velocities tended to mix the mixtures well and quickly,regardless of the density ratio of the two components.
Compound droplets surrounded by a gaseous phase with different temperatures widely exist in industrial applications. Previous research has focused on thermally induced non-coalescence or delayed coalescence between tw...
Compound droplets surrounded by a gaseous phase with different temperatures widely exist in industrial applications. Previous research has focused on thermally induced non-coalescence or delayed coalescence between two single-phase droplets or a droplet and a liquid bath. The primary mechanism is the levitated intervening pressure in the lubricating air layer between droplets, which is caused by the thermocapillary convection. In this study, the non-coalescence of two compound droplets in a cold ambient air environment is experimentally investigated. The thermocapillary mechanism manifests three distinct features. First, as the two compound droplets approach each other, the temperature of the contact side of each droplet increases because of reduced heat loss, a phenomenon termed as the contact-side heating effect. This creates a surface temperature gradient, inducing Marangoni stress and subsequent surface convection. Second, owing to the immiscibility of the two phases within each compound droplet, the thermocapillary convection develops independently in each phase, forming independent convection which cannot be observed in single-phase droplets . It was observed that the directions of the thermocapillary convection within the two droplets were correlated and always planar symmetric, which is different from the uncorrelated and opposite convection of two single-phase droplets. Third and most importantly, the thermocapillary convection in the oil phase entrains the air into the lubricating film between droplets, inhibiting their coalescence only when the oil/water interface is adjacent to the contact zone.
Presents a set of data for flow and heat transfer of finned-tube bundle under the condition of high air flow velocity. Air flow and heat transfer over a 4 1.; 4 （ columns 1.; rows） finned-tube heat exchanger w...
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Presents a set of data for flow and heat transfer of finned-tube bundle under the condition of high air flow velocity. Air flow and heat transfer over a 4 × 4 （ columns × rows） finned-tube heat exchanger with rectangular fins was investigated experimentally in a wind tunnel with constant wall temperatures condition. The air flow velocity based on the minimum flow cross-section area over flow channel ranged from 1..8 to 50. 2 m/s, the heal transfer rate ranged from 21.8 to47. 1.kW, and the air temperatures increase ranged from 1.. 9 to 1.. 8 ℃. The present results were compared with results calculated from correlations proposed by CSPE. For air flow velocity less than 25 m/s, these two results of heat transfer agreed well with each other, whereas for larger velocity, our test data disagreed with the CSPE correlations. For the friction factor, present data are much higher than the predicted results in the whole range. Finally, correlations for friction factors and heat transfer coefficients are DrODosed based on the experimental results.
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