水煤膏流变性能的试验研究

水煤膏的管内输送特性是增压流化床燃烧湿法加料技术研究中的一个十分重要的问题。该文通过试验研究，分析了水份、粒度配比、煤种及石灰石的添加等诸因素对水煤膏流动特性的影响，结果表明：通过适当的配比，水煤膏在很低的水份下（２４．３％）能够有良好的流动特性；而石灰石的加入也明显降低了水煤膏在管内的流动阻力。试验得到的流变参数表明：水煤膏的流变特性在高水份时，近似为宾汉体；而在低水份时，近似为幂律流体。图１１表２参４     

增压流化床用水煤膏在管内流动特性

通过试验研究水煤膏在中小管道中的流变特性和阻力特性,分析了各影响因素对水煤膏流变特性的影响,给出了水煤膏管内流动阻力的计算方法。研究表明,适当配比的水煤膏可以在很低水份下（22.16%）顺利流动,石灰石的添加和温度的提高可以降低水煤膏在管道内的流动阻力,水煤膏的流变特性可用Herschel-Bulkley模型描述。在层流状态下,水煤膏的阻力系数可用类似于牛顿流体的广义雷诺数表征,λ=64/Reg。     

增压流化床用水煤膏管道输送的研究

通过试验研究了水煤膏在中小管道中输送的流变特性和阻力特性,分析了各影响因素对水煤膏流变特笥的影响,给出了水煤膏管内流动阻力的计算方法,研究表明,水煤膏的流变特性可用Herschel-Bulkley模型描述,适当配比的水煤膏可以很低水份下（22．16％）顺利流动,石灰石的添加可以降低水煤膏在管道内的流动阻力,层流态态下,水煤膏的阻力系数可用似于牛顿流体的广义雷诺数描述即,λ＝64／Reg.     

增压流化床用水煤膏管内流动滑移效应研究

用实验方法在自制水煤膏流动试验台上研究了水煤膏的流变特性,分析了壁面滑移现象对水煤膏管内流动特性的影响,给出了通过滑移修正后的水煤膏真实流变模型,试验结果表明,水煤膏的流变模型符合Hrschel-Bulkey流体特征,滑移对管内流量的影响随着壁面剪切应力的减小而增加,随着管径的增加而减小。     

增压流化床燃烧用的煤水混合物流变特性研究

通过试验研究,系统分析了水分、配比、添加石灰石及管径变化等对水煤膏流变特性的影响。试验结果表明,通过适当的配制,水煤膏在很低的水分下（Wt=22.16%)能够获得良好的流动性能,石灰石的添加可以明显地降低水煤膏的管内阻力,改善水煤膏的输送性能,试验得到的流变参数表明,水煤膏的流变特性近似为宾汉体。     

水煤膏压力泌水特性与可泵性分析

通过实验研究了水煤膏的压力泌水特性,分析了颗粒粒度分布、含水量等对水煤膏的泵送特性的影响,并结合水煤膏塌落度指标,提出了水煤膏可泵性的评价指标。结果表明：水煤膏的可泵性可以用塌落度和压力泌水总量两个指标表征。可泵性好的水煤膏其塌落度范围为8-24cm,相应的相对泌水率和泌水总量分别为S10≤40%,V=70-110ml。     

水煤膏冷态雾化试验装置和测量系统的研究

建立了一套垂直式水煤膏雾化试验装置,提出了通过采用PIV技术及二将开发的图像处理软件来测量水煤膏雾化颗粒的平均粒径与分布的方法,分析了水煤膏雾化颗粒测量的影响因素,为进一步研究水煤膏喷嘴雾化性能提供了保证。     

向加压流化床添加水煤膏的试验研究

本文介绍了在１ＭＷｔ加压硫化床燃烧装置上进行水煤膏燃烧试验的情况，水煤膏由约７５％煤和２５％水组成，运行稳定，燃烧效率达９９．５％左右。     

双孔射流流化床内颗粒混合特性的离散单元法数值模拟

将计算流体力学与离散单元法相结合,采用Fortran语言编程,根据牛顿第三定律实现气固耦合,从微观角度剖析了颗粒在流化床内的运动机制.利用Lacey混合指数对流化床内不同特性区域的颗粒混合程度进行了定量分析,并研究了颗粒混合特性的影响因素,得到颗粒轴向和径向混合序列图、气体和颗粒速度分布以及整床和三区的颗粒混合指数分布.结果表明:颗粒受到空气射流作用后,随着混合和偏析的不断进行,最后达到随机完全混合状态;相同表观气速下颗粒轴向混合进程快于径向混合进程;表观气速增大,喷泉区尺度增大,使颗粒径向混合能力得到改善,但对轴向混合能力的影响微弱.     

300 MW单炉膛循环流化床锅炉二次风射程的数值模拟

针对大型循环流化床中二次风射流的特性,采用Fluent数值计算软件对300 MW单炉膛大型循环流化床锅炉炉膛进行了数值模拟,研究了二次风口高度、二次风射流角度、二次风风速、一次风风速和炉内颗粒浓度对二次风穿透性和气固两相混合的影响.结果表明:二次风射流深度随着一次风风速的增大和颗粒浓度的提高而减小;当二次风射流速度增大时,射流深度增加;二次风射流角度和二次风喷口位置也会影响二次风射流深度.     

Visualization of a turbulent jet using wavelets

ho-cttonCoherent strUctUres are known to ealst and areresPOnsible for most of the momentUIn transfer inndulent jets. Many identification techniques, such asimage processing, sPeCtI'a analysis, spatial correlationfimctions, education schemes, PrOper OrthOgonaldecomposihon, stOChastic eshInation, pattem recoghhon,and wave1et tusform, are wen established to detennincoheret stI'Ucwts. Howevee the local scales with resPeCtto spacehme change continously for the turblence andthe coheren stheA…     

Mixing performance of transverse hydrogen/air multi-jet through coaxial injector arrays in supersonic crossflow

Increasing the fuel mixing performance substantially improves the overall performance of the scramjet engine for a long-distance flight. In this paper, the influence of coaxial injector arrays of hydrogen/air multi-jet on the mixing performance of the fuel in supersonic crossflow is fully investigated. Our main goal is to examine the impacts of air and fuel coaxial injector on fuel distribution and penetration downstream of injectors in different operating conditions. In this study, fuel and air are simultaneously injected through coaxial multi-jet at sonic condition while of free-stream Mach number is 4. Computational Fluid Dynamic is applied for simulation of the transverse coaxial jet at supersonic crossflow. The effect of jet diameter with the same mass flow rate of air and hydrogen on fuel mixing is also investigated. The mixing efficiency of different jet spaces and pressures is also examined to obtain an optimum jet arrangement in the combustor chamber. Our study shows that the injection of the coaxial air/hydrogen jet noticeably improves mixing downstream by augmentation of fuel interaction with an air jet. Our results also show that fuel jet space of 7 Dj offers maximum fuel mixing by the formation of multi vortices with uniform strength.     

The effect of chemical reaction on the mixing flow between aqueous solutions of acetic acid and ammonia

The basic characteristics of the reacting mixing flow of two streams were investigated. The reaction between aqueous solutions of ammonia and acetic acid, which produces ammonium acetate, was investigated in terms of the effect on the fluid–fluid interface of the mixing flow relative to fluids that did not react. The reaction between these solutions was negligibly exothermic, and there were minimal differences in density. The velocity field in the reacting mixing flow was quantitatively measured using high-speed time-resolved particle image velocimetry (PIV) and the behavior of the mixing flow was qualitatively investigated using laser-induced fluorescence (LIF). The jet width, the velocity field, the kinetic energy and the turbulent intensities are qualitatively estimated and discussed. It was found that the chemical reaction resulted in the suppression of the mixing flow.     

Numerical study of injection strategy based on cavity combustor under oblique shock wave interference

In this study, the effect of jet injection strategy on the mixing performance of ethylene jets is investigated. Numerical simulations are carried out using the SST k-ω turbulence model and steady RANS. Mesh-independence verification is performed using experimental data from the open literature. The mixing performance, penetration depth, and total pressure loss of the ethylene jets with different injection angles and injection numbers are compared and analyzed. The analysis reveals that the interaction between the ethylene jets in the double-hole jet facilitated the mixing process and has a significant mixing effect in the vicinity of the nozzle. The mixing efficiency of the two-hole jet near the injection nozzle is about 43.4% higher than that of the 90° jet. The vertical incidence still dominates in the penetration depth. The ethylene diffusion distribution of the double-hole jet is more uniform, so the penetration depth of the double-hole jet does not increase, but decays more slowly downstream. In addition, the jet injection strategy has almost no effect on the total pressure loss.     

Turbulent mixing of a passive scalar in confined multiple jet flows of a micro combustor

The turbulent mixing characteristics of multiple jet flows in a micro can type combustor are investigated by means of large eddy simulation (LES). The micro combustor can be used for a micro gas turbine which is hybridized with solid oxide fuel cell. Attention is paid for a micro combustor having a circular disk baffle plate with a fuel injection nozzle in the center and oxidant injection holes allocated annularly. Downstream the baffle plate, a complex flow is produced from the interaction of multiple jet flows and study is made for three different configurations of the baffle plates resulting in different mixing pattern. From the results, it is substantiated that the turbulent mixing is promoted by complex flow fields caused by the jet flows and large vortical flow regions in the micro combustor. This is effective to accelerate the slow mixing between fuel and oxidant suffering from low Reynolds number in such a small combustor. In particular, the vortical flow region formed downstream the fuel jet core region plays an important role for rapid mixing coupled with another flow recirculation region. Discussion is made for the instantaneous and time and space averaged flow and passive scalar quantities which show peculiar turbulent flow and mixing characteristics corresponding to the different flow structures for each baffle plate shapes, respectively.     

The influence of annular lobe-injector on the fuel mixing of hydrogen jet at supersonic combustion chamber

The performance of the engine highly depends on the fuel mixing process as a significant process to achieve efficient supersonic flight. Current article has attempted to release the effects of different annular lobe-injectors on fuel mixing when Ma>1. Three various annular jet nozzles are expansively investigated for injection of the sonic hydrogen jet at supersonic air crossflow with Mach-4. Comprehensive comparison of the jet structure of these models are performed through the evaluation of Mach and fuel concentration downstream of these lobe-injectors. Comparison of mixing efficiency also indicates that the nozzle with 3-lobe configuration has 25% more fuel mixing performance than other configurations. Our findings also show that mixing performance of annular lobe-injector is about 15% more than simple one for cases with 2-lobe and 4-lobe injectors.     

Influence of coaxial air jet on mass diffusion of hydrogen jet injected through lobe-injector at supersonic flow

The technique of fuel injection in the combustion chamber is crucial for increasing the performance of hypersonic vehicles. This study tries to investigate the mechanism of fuel injection and distribution when fuel and air are injected through coaxial lobe injectors. The main attention of this work is to present the mechanism of fuel mixing of transverse jet injected from various lobe injectors. Comparison of coaxial gets (air and fuel jet) with equivalent simple jet (fuel without air jet) is done to achieve an efficient model for the combustion chamber. In this work, finite-volume is used to simulate and study of fuel injection performance of a transverse hydrogen jet in different lobe injectors. 3-D flow visualizations are done to reveal the mechanism of the fuel penetration and streamline pattern for introduced models. Strength of circulation and fuel mixing efficiency are also investigated in the present work for 2-, 3-, and 4-lobe nozzles. Our outcomes indicate that the mixing performance of coaxial air and fuel jet injected through the 3-lobe nozzle is about 25% better than other nozzle types. Our findings confirm that injection of air jet through the core of the lobe nozzle increases fuel mixing up to 200% at the combustion chamber.     

Effect of jet schemes of the double-nozzle strut injector on mixing efficiency of air and hydrogen for a scramjet combustor

This work presents the numerical analysis of the DLR scramjet combustor for different jet schemes of the double-nozzle injector, namely the various injection directions, injection angles, and nozzle spacings. After comparing various jet schemes, it is found that the optimal jet scheme for the double-nozzle strut is to set the angle of 60° for the inward injection direction and the nozzle spacing of 3 mm. Furthermore, the mixing efficiency of the optimal jet scheme is investigated at different Mach numbers. The current research focuses on the mixing mechanism of air and hydrogen by analyzing the flow structures in the strut's wake region. It is observed that the double-nozzle configuration increases the number of vortexes behind the strut and creates a recirculation zone between the two jet streams. The mixing efficiency of the scramjet combustor improves significantly with an increase in the injection angle, but the spacing and direction of the double-nozzle have little effect on the mixing efficiency. It is found that the additional total pressure loss generated by the double-nozzle configuration can be negligible. In addition, the results show that the mixing efficiency of the optimal jet scheme for the double-nozzle is improved more significantly at low Mach numbers (e.g., Ma = 2 and 3).     

Visualization of flow and heat transfer characteristics for swirling impinging jet

Flow and heat transfer characteristics of swirling impinging jet (SIJ) were studied experimentally at constant nozzle-to-plate distance of L = 4D. The swirling jet is generated by inserting twisted tapes within a pipe nozzle. Effects of swirl on the impinged surface are investigated at twist ratios (y/W) of ∞ (straight tape), 3.64, 2.27, 1.82, and 1.52. The flow patterns of the free swirling jet and the swirling impinging jet were visualized by mixing dye with the jet flow. Distributions of temperature and convective heat transfer coefficient on the impinged surface were measured with thermochromic liquid crystal (TLC) sheet and image processing technique. Additionally, an oil film technique was performed as a complementary technique for flow visualization on the impinged surface. The experimental results reveal that there appear to be two peaks of heat transfer in the jet impingement region. The heat transfer enhancements in jet impingement region can be achieved at a low twist ratio of 3.64 which corresponds to the swirl number of 0.4.     

URANS study of pulsed hydrogen jet characteristics and mixing enhancement in supersonic crossflow

In this paper, three-dimensional pulsed hydrogen jet in supersonic crossflow (PJISC) is investigated by the unsteady Reynolds Averaged Navier-Stokes (URANS) simulations with the k-ω shear stress transport (SST) turbulence model. The numerical validation and mesh resolution have been carried out against experiment firstly. The effects of the pulsed frequency and amplitude on the jet flow field and mixing performance in supersonic cross-flow are all addressed. It significantly changes the distribution of the hydrogen jet flow by comparing with the steady jet in supersonic crossflow. The fuel jet penetration, mixing efficiency, decay rate of the maximum hydrogen mass fraction and total pressure losses are used to quantitatively analyze the mixing performance. The mixing of fuel and incoming air flow is enhanced by the pulsed jet, especially for the case of 50 kHz, which is the optimal pulsed frequency while considering the effects of jet excitation frequency in the present simulations. The decay rate of the maximum mass fraction of hydrogen in the far field downstream is related to the frequency of the pulse jet. Moreover, the pulsed frequency and amplitude have little effects on the total pressure recovery coefficient for the cases studied in the present simulations.