新型气液逆流撞击洗涤喷嘴的优化

针对一种新型气液逆流撞击式洗涤喷嘴,通过冷模实验,采用溶氧法考察了不同结构喷嘴的气液两相传质性能。结合解析率及流型变化,考察了喷嘴出口直径、切向进液口倾角、旋流室收敛段锥角、切向进液口直径、喷口长度5个参数对传质的影响,确定了优选喷嘴的结构尺寸,分析了该优选喷嘴在不同操作条件下(气速、表观液气比和轴切比)的传质效果。结果表明,优选喷嘴在轴切比为0.4~0.6且气速较高时传质效果较好。     

Numerical simulation of flow focusing pattern and morphological changes in two-phase flow inside nozzle

The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase.The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear.The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method.The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas–liquid velocity ratio, and capillary diameter have significant effects on the flow pattern.When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas–liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form.Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate,and cone angle in order to study the morphological changes in the cone shape inside the nozzle.The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated.When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.     

Study of Hydrodynamics,Mixing and Gas‐Liquid Mass Transfer in a Split‐Rectangular Airlift Reactor

Global hydrodynamic characteristics, liquid mixing and gas‐liquid mass transfer for a 63 L split‐rectangular airlift reactor were studied. Correlations for gas holdup and overall liquid circulation velocity were derived for the air‐water system as a function of the specific power input; these were compared to data and correlations for reactor volumes between 4.7 L and 4600 L. A partial recirculation of small bubbles in the riser was observed when U_gr > 0.03 m/s, which was attributed to the use of a single‐orifice nozzle as the gas phase distributor. The dimensionless mixing time and the overall axial dispersion coefficient were nearly constant for the range of gas flow rates studied. However, values of K_L/d_B were greater than those reported in previous studies and this is caused by the partial recirculation of the gas phase in the riser. While scale effects remain slight, the use of a gas distributor favouring this partial recirculation seems adequate for mass transfer in split‐rectangular airlift reactors.     

Numerical investigation of spinneret geometric effect on spinning dynamics of dry‐jet wet‐spinning of cellulose/[BMIM]Cl solution

In this study, the effect of spinneret geometry, including the entrance angle α of the entrance channel, the length L_s, and the diameter D₀ of the exit channel, on the spinning dynamics of dry‐jet wet‐spinning of cellulose/1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) solution was simulated by using finite element method. Based on the mathematical model of dry‐jet wet‐spinning established in our previous work (Xia et al., Cellulose 2015, 22, 1963) the radial and axial profiles of velocity, pressure, and shear rate in the spinneret and the profiles of diameter, temperature, and tensile stress in the air‐gap region were obtained. From the simulated profiles, the effect of spinneret geometric parameters on the flow behavior and the pressure drop of polymer solution in the spinneret and the die‐swell ratio near the spinneret was discussed. The entrance angle α of the entrance channel mainly influences the flow behavior of polymer solution in the spinneret and the die‐swell effect near the spinneret. As the decrease of the entrance angle α of the entrance channel, the vortices in the spinneret could be removed and the die‐swell ratio decreases. The increase of the length L_s of the exit channel results in the increase of pressure drop in the spinneret and the decrease of the die‐swell ratio. It is also found that the increase of the diameter D₀ of the exit channel reduces the flow velocity of polymer solution and decreases the pressure drop in the spinneret at a constant mass flow rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43962.     

Distribution of Two‐Phase Flow across 2.7‐mm Vertically Split U‐Type Junctions

A visual observation of the two‐phase flow across vertically split U‐type junctions and its flow redistribution inside two 2.7‐mm diameter smooth tubes with curvature ratios (2R/D) of 3 and 7, respectively, are reported. The range of mass flux is between 100 and 700 kg/m²s and quality (x) ranges from 0.001 to 0.5. The ratio of liquid distribution between the upper and lower outlet legs is related to the inlet flow pattern, but its influence is reduced at higher mass flux. The difference in liquid flow rates in the lower and upper legs is significantly affected by gravity at a small inlet mass flux, but this difference becomes less profound when the inlet mass flux is increased. The difference between the liquid flux in the upper and lower leg is reduced for the smaller curvature radius due to the reduced effect of gravity between the upper and lower legs. However, there is no consistent trend of gas flow distribution across the U‐type junction as compared to liquid flow distribution. The air mass flux in the upper and lower legs always increase with an increase in both gas quality and the total mass flux.     

Gas‐Liquid Mass Transfer in Fibrous Bed Reactor with Counter‐Current Liquid Recycle

In this work, the gas‐liquid mass transfer in a lab‐scale fibrous bed reactor with liquid recycle was studied. The volumetric gas‐liquid mass transfer coefficient, k_La, is determined over a range of the superficial liquid velocity (0.0042–0.0126 m.s^–1), gas velocity (0.006–0.021 m.s^–1), surface tension (35–72 mN/m), and viscosity (1–6 mPa.s). Increasing fluid velocities and viscosity, and decreasing interfacial tension, the volumetric oxygen transfer coefficient increased. In contrast to the case of co‐current flow, the effect of gas superficial velocity was found to be more significant than the liquid superficial velocity. This behavior is explained by variation of the coalescing gas fraction and the reduction in bubble size. A correlation for k_La is proposed. The predicted values deviate within ± 15 % from the experimental values, thus, implying that the equation can be used to predict gas‐liquid mass transfer rates in fibrous bed recycle bioreactors.     

Experimental Study of Spray Drying and Atomization with a Two-Fluid Nozzle to Produce Inhalable Particles

A series of 50 experiments was performed to investigate particle size and yield from three laboratory spray dryers with two-fluid nozzles, using an aqueous solution of egg albumin as the feed. First principles theory suggests that the main parameters affecting final particle size should be atomization gas flowrate and velocity, feed solution flowrate, solution concentration, and inlet and outlet gas temperature. The experiments demonstrated that atomization gas velocity at the nozzle correlated better than volumetric gas flowrate to the final particle size obtained. Increasing atomization gas flow gave a decrease in particle size, levelling off at high nozzle gas velocities approaching sonic values. Liquid flowrate had little effect, and hybrid ratios such as the ALM (atomization gas to liquid flow ratio) did not correlate well to measured final particle size for this system. This seems likely to apply to aqueous systems with temperature limitations, where liquid flowrates will be relatively low compared to gas flowrates (both atomization and main gas flow). Particle size generally increased with solution concentration, and in some cases scaled exactly, assuming a constant initial droplet size and final particle density. All experiments were performed below the boiling point and therefore temperature had little effect. Particles of 2–3 microns were obtained at high atomization gas flows, indicating initial droplet sizes of 4–7 microns at most, while lower flowrates gave substantially larger particles and a wider size distribution.     

Studies on the hydrodynamic behavior and mass transfer in a down‐flow jet loop reactor with a coaxial draft tube

The effects of certain pertinent parameters such as gas and liquid flow rates and nozzle position on the behavior of a down‐flow jet loop reactor (DJR) have been studied. The mean residence times of gas and liquid phases and the gas holdup within the reactor have been measured. In addition, the overall volumetric mass transfer coefficient, and the influence of the gas flow rate and the position of the nozzle inside the draft tube on the latter has been determined. Correlations have been presented for the gas holdup and k_La which take into account the length of the draft tube and the nozzle immersion height. The k_La values obtained at different power per unit volume (P/V) values in the DJR used in the present study compare favorably with data presented for stirred tanks and bubble columns in the literature. The liquid residence time distribution (RTD) within the reactor has been studied by tracer analysis for various operating conditions and nozzle immersion height and the results are indicative of the high mixing intensities that can be obtained in such reactions. © 2001 Society of Chemical Industry     

重油燃烧器Y型喷嘴气液两相流动与雾化特性模拟

为改善重油雾化质量,针对沥青站重油燃烧器Y型喷嘴,运用CFD (Computational Fluid Dynamics)方法研究了喷嘴结构参数(混合室长度、入口直径比、入口夹角)与雾化参数(重油流量、空气入口压力、重油温度)对喷嘴气液两相流动与雾化特性的影响。结果表明,结构参数与雾化参数直接影响喷嘴内油膜厚度与气液两相速度差;不同参数下,喷嘴气耗率与液滴索泰尔平均直径的变化规律相反;综合考虑两个雾化性能指标,混合室的适宜长度为15~20 mm,入口夹角的合理范围为60°~75°,入口最佳直径比为1.0~1.1;为保证重油获得较好的雾化效果,空气入口压力应大于0.5 MPa,这为优化Y型雾化喷嘴的结构与运行参数提供了参考。     

Atomization of Liquids by Two‐phase Gas‐liquid Flow through a Plain‐orifice Nozzle: Flow Regimes inside the Nozzle

Liquids or suspensions are divided into sprays of small droplets by atomization of two‐phase gas‐liquid mixtures. In this way either an equal distribution of the droplets or the generation of large surface areas of the liquid phase are accomplished, leading to increased heat‐ and mass‐transfer. The spatial and time dependency of the mean droplet diameter is a function of the total pressure upstream of the nozzle, the volumetric flow rate of the liquid and the gas, as well as on the flow regime in the nozzle. Thus the radial and axial profile of the void fraction inside the nozzle are measured with an electrical measurement technique. In addition, the flow in the nozzle is imaged by a high‐speed camera. Three flow regimes are identified. These are bubbly flow, plug flow and annular flow. A continuous flow of the emitting spray is observed for bubbly flow and annular flow only. The distribution of the dispersed bubble phase is given by ratio of the isothermic compression energy needed to pressurize the gas mass flow rate from atmospheric pressure up to the total pressure in front of the nozzle, and the potential energy of the supplied liquid mass flow rate.     

Simulation and Experimental Validation of Two‐Phase Flow in an Aerosol Counter‐Flow Reactor using Computational Fluid Dynamics

A simulation of the hydrodynamic behavior of an aerosol‐counter flow reactor was conducted using an Euler‐Lagrange method. The simulation results were then verified with experiments. The process simulated was a separation process required during the production of biodiesel (fatty acid methyl ester). In this process, the liquid ester/glycerol phases are continuously injected through a hollow cone nozzle with an overpressure of 10⁶ Pa into the reactor, operated at 15000 Pa. The liquid is atomized because of the pressure drop and a liquid particle spray is generated with an inlet velocity of 44.72 m/s. Water vapor of temperature 333 K is injected tangentially through two side, gas inlets with an inlet velocity of 1.2 m/s. Excess methanol is subjected to a mass transfer from the liquid phase into the gas phase, which is withdrawn through the head of the reactor and condensed in an external condenser unit. The stripping of the methanol off the liquid leads to a sharp interface between the glycerol and the ester phase, which can then be easily separated by gravity or pumping. The gas velocity field, pressure field and the liquid particle trajectories were calculated successfully. Simulated dwell time distribution curves were derived and analyzed with the open‐open vessel dispersion model. Experimental dwell time distribution curves were measured, analyzed with the open‐open vessel dispersion model, and compared with the simulated curves. A good consistency between simulated and measured Bodenstein numbers was achieved, but 25 % of the simulated particles exited at the reactor's head, contrary to experimental observations. The difference between simulated and measured dwell times was within one order of magnitude.     

Pressure drop for single and two‐phase flow of non‐newtonian liquids in helical coils

New experimental results on pressure loss for the single and two‐phase gas‐liquid flow with non‐Newtonian liquids in helical coils are reported. For a constant value of the curvature ratio, the value of the helix angle of the coils is varied from 2.56° to 9.37°. For single phase flow, the effect of helix angle on pressure loss is found to be negligible in laminar flow regime but pressure loss increases with the increasing value of helix angle in turbulent flow conditions. On the other hand, for the two‐phase flow, the well‐known Lockhart‐Martinelli method correlates the present results for all values of helix angle (2.56‐9.37°) satisfactorily under turbulent/laminar and turbulent/turbulent conditions over the following ranges of variables as: 0.57 ≤ n′ ≤ 1; Re′ < 4000; Re_l < 4000; Re_g < 8000; 8 ≤ x ≤ 1000 and 0.2 ≤ De′ ≤ 1000.     

Volumetric Mass Transfer Coefficient in non‐Newtonian Fluids in Spout Fluid Beds

The volumetric liquid‐phase mass transfer coefficient, k_La, was determined by absorption of oxygen in air using six different carboxy‐methyl cellulose (CMC) solutions with different rheological values in three phase spout‐fluid beds operated continuously with respect to both gas and liquid. Three cylindrical columns of 7.4 cm, 11.4 cm, and 14.4 cm diameters were used. Gas velocity was varied between 0.00154–0.00563 m/s, liquid velocity between 0.0116–0.0387 m/s, surface tension between 0.00416–0.0189 N/m, static bed height between 6.0–10.8 cm, and spherical glass particles of 1.75 mm diameter were used as packing material. A single nozzle sparger of 1.0 cm diameter was used in the spouting line. The volumetric mass transfer coefficient was found to increase with gas velocity, liquid velocity, and static bed height and to decrease with the increase of the effective liquid viscosity of the CMC solution. A dimensionless correlation was developed and compared with those listed in the literature.     

Dynamic modeling and simulations of the behavior of a fixed‐bed reactor‐exchanger used for CO2 methanation

A multidimensional heterogeneous and dynamic model of a fixed‐bed heat exchanger reactor used for CO₂ methanation has been developed in this work that is based on mass, energy and momentum balances in the gas phase and mass and energy balances for the catalyst phase. The dynamic behavior of this reactor is simulated for transient variations in inlet gas temperature, cooling temperature, gas inlet flow rate, and outlet pressure. Simulation results showed that wrong‐way behaviors can occur for any abrupt temperature changes. Conversely, temperature ramp changes enable to attenuate and even fade the wrong‐way behavior. Traveling hot spots appear only when the change of an operating condition shifts the reactor from an ignited steady state to a non‐ignited one. Inlet gas flow rate variations reveal overshoots and undershoots of the reactor maximum temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 468–480, 2018     

Hydrodynamics,Mass Transfer and Gas Scrubbing in a Co‐current Droplet Column Operating at High Gas Velocities

The main objective of this work was to propose a new process for household fume incineration treatment: the droplet column. A feature of this upward gas‐liquid reactor which makes it original, is to use high superficial gas velocities (13 m s^–1) which allow acid gas scrubbing at low energy costs. Tests were conducted to characterize the hydrodynamics, mass transfer performances, and acid gas scrubbing under various conditions of superficial gas velocity (from 10.0 to 12.0 m s^–1) and superficial liquid velocity (from 9.4·10^–3 to 18.9·10^–3 m s^–1). The following parameters characterized the hydrodynamics: pressure drops, liquid hold‐ups, and liquid residence time distribution were identified and investigated with respect to flow conditions. To characterize mass transfer in the droplet column, three parameters were determined: the gas‐liquid interfacial area (a), the liquid‐phase volumetric mass transfer coefficient (k_La) and the gas‐phase volumetric mass transfer coefficient (k_Ga). Gas absorption with chemical reaction methods were applied to evaluate a and k_Ga, while a physical absorption method was used to estimate k_La. The influence of the gas and liquid velocities on a, k_La, and k_Ga were investigated. Furthermore, tests were conducted to examine the utility of the droplet column for the acid gas scrubbing, of gases like hydrogen chloride (HCl) and sulfur dioxide (SO₂). This is a process of high efficiency and the amount of pollutants in the cleaned air is always much lower than the regulatory European standards imposed on household waste incinerators.     

Numerical Study on the Effect of Cavitation on Flow and Diesel Fuel Atomization Characteristics

Computational fluid dynamics (CFD) models based on the turbulent mixture multiphase model were applied to consider the effect of cavitation on the spray of diesel fuel. The effects of injection pressure and length‐to‐width (L/W) ratio on the velocity distribution, cavitation number, discharged coefficient, and nozzle exit velocity were investigated and the performance of the model was compared with the experimental data. The results indicate that the cavitation generated in the nozzle has a strong impact on the fuel injection and spray quality, whereas the L/W ratio is a highly effective parameter for cavitation behavior. In addition, by increasing the L/W ratio, the range of cavitation number, wall friction, and flow resistance increase but in the cavitation region the velocity profile in radial and axial directions, spray cone angle, nozzle exit velocity, and the discharged coefficient decrease.     

甲醇制丙烯反应器喷嘴雾化性能的研究

雾化喷嘴系甲醇制丙烯（MTP）反应器内的关键反应物料分配构件,其雾化性能的优劣直接影响着对应催化床层覆盖区域内的传质和传热,从而影响到床层出口反应产物的分布。以反应器六级床层对应的雾化喷嘴为研究对象,分别以氮气（N₂）和水（H₂O）作为气相和液相模拟介质,通过“冷模”实验,考察了喷嘴气（液）流量与入口压力之间的关系,研究了喷嘴在不同气液比（G/L）下雾化粒径、雾化角度及雾化覆盖直径的变化规律。实验结果表明,喷嘴液相质量流量随着入口压力增大而逐渐增加,气相质量流量随着入口压力增加而迅速增加;当保持液相进料量为43.54 kg/h时,喷嘴由一次雾化变为二次雾化后,雾化角度由96.1°降至15.6°;当气液质量比G/L达到12.19时,雾化覆盖直径达到720mm,且雾滴的索泰尔平均粒径为16.3μm。     

Measurement of mass transfer coefficient in an airlift reactor with internal loop using coalescent and non‐coalescent liquid media

In this work the sulfite oxidation (SOM), dynamic pressure‐step (DPM) and gassing‐out (GOM) methods were compared for volumetric mass transfer coefficient measurement in an airlift reactor with internal loop. As a liquid phase both, non‐coalescent and coalescent media were used. Among the methods discussed here, the mass transfer coefficient (k_La) values obtained by the DPM appear as the most reliable as they were found to be independent of oxygen concentration in the inlet gas, which confirmed the physical correctness of this method. The difference between data measured using air and oxygen was not higher than 10%, which was comparable to the scatter of experimental data. It has been found that the sulfite oxidation method yielded k_La values only a little higher than those obtained by the DPM and the difference did not exceed 10%. Up to an inlet gas velocity (U_GC) of ?0.03 m s^?1 the GOM using oxygen as a gas medium gave k_La values in fact identical with those obtained by the DPM. At higher flows of the inlet gas, the GOM yielded k_La values as much as 15% lower. The enhancement in oxygen mass transfer rate determined in non‐coalescent media was estimated to be up to +15%, when compared with a coalescent batch. The experimental dependence of k_La vs the overall gas hold‐up was described by an empirical correlation. 1 Copyright © 2004 Society of Chemical Industry     

Mass transfer and hydrodynamic characteristics in a co‐current downflow contacting column

Hydrodynamic and mass transfer characteristics of water–air system in a co‐current downflow contacting column (CDCC) were studied for various nozzle diameters at different superficial gas velocities and liquid re‐circulation rates. Gas hold‐up and liquid‐side mass transfer coefficient increased with increasing superficial gas velocity and liquid flow rate but decreased with increasing nozzle diameter. It is shown that correlations developed, which are based on liquid kinetic power per liquid volume present in the column, and superficial gas velocity explains gas hold‐up and the mass transfer coefficient within an error 20% for all gas and liquid flow rates and nozzle diameters used. The constants of correlations for gas hold‐up and mass transfer coefficient were found to be considerably different from other gas–liquid contacting systems. © 2003 Society of Chemical Industry     

4,5‐Bis(5‐tetrazolyl)‐1,2,3‐triazole: Synthesis and Performance

4,5‐Bis(5‐tetrazolyl)‐1,2,3‐triazole (BTT) was synthesized by a new method. Its structure was characterized by IR and ¹³C NMR spectroscopy and elemental analysis (EA). The thermal stability of BTT was investigated by TG‐DSC technique. The kinetic parameters including activation energy and pro‐exponential factor were calculated by Kissinger equation. The combustion heat, detonation products, hygroscopicity, impact, and friction sensitivity were also measured. The formation heat, detonation pressure, and detonation velocity of BTT were calculated. BTT has high detonation pressure and detonation velocity (P=35.36 GPa, D=8.971 km s⁻¹). BTT has potential application prospect as environmentally friendly gas generant, insensitive explosive and solid propellant.