Effect of Nozzle Geometry on the Flow Characteristics of Spiral Flow Generated through an Annular Slit

In comparison with previous researches of swirling flow,spiral flow generated in the spiral nozzle has some differentflow characteristics.It does not need a forced tangential momentum to generate its velocity and has some differentmerits from the swirling flow such as long potential core and low tangential velocity.In this study,the effect of noz-zle geometry on the flow characteristics in spiral nozzle was investigated by experiment and computation.As a result,the flow characteristics obtained by experiment has a satisfactory agreement with computational results,quantita-tively and qualitatively.     

Effect of Annular Slit Geometry on Characteristics of Spiral Jet

A spiral flow using an annular slit connected to a conical cylinder does not need special device to generate a tangential velocity component of the flow and differs from swirling flows. Pressurized fluid is supplied to an annular chamber and injected into the convergent nozzle through the annular slit. The annular jet develops into the spiral flow. In the present study, a spiral jet discharged out of nozzle exit was obtained by using a convergent nozzle and an annular slit set in nozzle inlet, and the effect of annular slit geometry on characteristics of the spiral jet was investigated by using a Laser Doppler Velocimeter (LDV) experimentally. Furthermore, velocity distributions of the spiral jet were compared with those of a normal jet.     

增压富氧燃煤锅炉省煤器的设计与优化

以300MW机组煤粉炉省煤器为例,对锅炉常压空气燃烧、常压富氧燃烧和5种不同增压(6MPa)富氧燃烧方案下的锅炉对流受热面尺寸、烟气流量、烟气侧传热系数和压降等参数进行了计算和分析,根据基于经济性分析的单位换热量换热器总费用最小的原则确定省煤器的最佳设计结构.结果表明:与常压空气燃烧相比,常压富氧燃烧下烟气体积流量减小了28.5%,对流传热系数减小了11.5%;增压富氧燃烧下的烟气体积流量减小了98.82%,随着烟气流速的增大,受热面面积减小,烟气侧传热系数和压降增大;最佳方案中的烟气流速为1.54m/s时,单位换热量换热器总费用约为常压空气燃烧下的60%,烟气侧压降为582.65Pa,烟道截面积仅为常压空气燃烧下的7.8%.     

螺旋形实心锥喷嘴雾化特性试验研究

为了对氨法脱硫用螺旋形实心锥喷嘴的雾化特性进行准确预测,基于高速阴影技术和图像处理方法,对两种不同螺旋升角的螺旋形实心锥喷嘴的流量特性、喷雾场结构特征、雾化角变化规律、破碎长度、液滴空间分布及平均粒径进行分析。结合脱硫常用的空心锥离心式喷嘴,开展了两种喷嘴的稳定性对比分析。结果表明:螺旋形实心锥喷嘴的流量特性与螺旋升角无关,其喷雾场呈螺旋状同心锥面分布,雾化后液滴也呈螺旋形多层次分布,即实心锥分布;螺旋形实心锥喷嘴雾化角在喷注压降大于0.05 MPa时与螺旋形升角有关,与流量和喷注压降无关;考虑螺旋面升角对液滴平均粒径的影响,得到了新的索太尔平均直径(SMD)经验关系式,预测结果与试验结果趋势一致,且螺旋升角越大,液滴平均粒径越小;螺旋形实心锥喷嘴在喷注压降小于0.05 MPa时也能保证稳定雾化,而空心锥离心式喷嘴会出现约为9 Hz的自激振荡现象,喷雾场呈"宝塔形",且具有明显的Klystron效应。     

进口结构对方形旋风分离器性能影响的数值研究

利用CFD模拟研究了一种具有双矩形进口的方形截面的旋风分离器内部的流动特点,其中气相模型采用了雷诺应力湍流模型（Reynolds stress model,RSM）,颗粒相采用随机轨道模型。计算结果与文献实验数据的对比表明模型具有可靠性。模拟结果表明：在分离器内部的排气管和分离器壁面间的区域为强旋湍流区,靠近分离器壁面和排气管壁面的区域旋流强度较弱;排气管下的分离器内出现了回流;进口结构影响分离器内的旋流分布特点和回流开始位置及湍动能的分布,从而影响了分离效率和阻力,其中倾斜双进口的方形分离器内旋转向下的气流运动区域更大,回流开始位置更低,因此其分离效果更好;进口结构影响分离器内局部湍动能的分布特点和大小,从而决定了分离器的阻力大小;倾斜双进口的方形分离器内的局部湍动能小于对应的垂直单、双进口分离器,因此其阻力系数最小。     

Research on the Performance of Supercritical CO_2 Dry Gas Seal with Different Deep Spiral Groove

The performance of supercritical CO_2(SCO_2) dry gas seal(DGS) with different deep spiral groove is investigated with the thermal-fluid-solid coupling method. The performance parameters of DGSs with five different kinds of grooves are obtained. The influence of inlet temperature, inlet pressure, velocity and film thickness on performance is analyzed compared with air DGS. The average film pressure, open force and leakage decrease while the average face temperature and flow velocity increase as the spiral groove number increases. The average film pressure, average face temperature, open force and leakage of DGS with radial different deep groove are higher than those of DGS with circumferential different deep groove respectively under the same spiral groove number while the average flow velocity is the opposite. SCO_2 DGS can generate larger average film pressure, open force and leakage with lower average face temperature than air DGS. SCO_2 DGS could maintain better sealing performance despite larger leakage with the variations of inlet temperature, inlet pressure, velocity and film thickness. The variables hold a more remarkable influence on SCO_2 DGS compared with air DGS.     

掺混燃油在离心喷嘴内的流动与雾化特性研究

燃料性质的改变会导致雾化特性的变化,针对乙醇掺混航空煤油在离心式压力雾化喷嘴内的流动与雾化特性开展了研究。通过耦合流体体积法(VOF)和离散相模型(DPM),研究了不同乙醇掺混体积分数下掺混燃油在离心式喷嘴中的内部流动和外部雾化过程。研究结果表明：在压差不变时,喷嘴内空气芯直径随着掺混燃油内乙醇体积分数的增加而增大;而液膜厚度则与空气芯直径成反比,随着乙醇体积分数的增加而减小。喷嘴出口的速度随着乙醇体积分数的增加而增大;在油膜表面的波动及气动力的共同作用下,油膜失稳形成液滴,获得了不同比例下掺混燃油在喷雾外流场内的喷雾粒径分布特征,随着掺混乙醇体积分数的增加,液滴的平均直径逐渐减小。     

Experimental and theoretical studies on air humidification by a water spray at elevated pressure

Humidification of compressed air is important for humid air turbine cycle. In this paper, theoretical and experimental investigations are carried out to analyze and predict the humidification process in spray tower.For predicting the heat and mass transfer in the water droplet–air two-phase flow, a one-dimensional numerical model simulating the conservation of heat and mass of water and humid air was developed. The model considers the effect of droplet motion on the heat and mass transfer. Experimental data were obtained on a pressurized model spray tower at different pressures and water/air ratios, which had been adopted to validate the numerical model. Droplet diameter of the spray was measured and these data were used in the model. Predictions of outlet conditions of air and water for giving input conditions agree well with experimental data, which produces a maximal error of 7.3%. On the basis of the model, distributions of droplet velocity and volumetric heat transfer coefficient over height of the tower are predicted. The effect of droplet diameter on the characteristic performance of spray humidifier is also analyzed in the simulation.     

An investigation of the combustion of pulverized coal-air mixture in different combustor geometries

A two-dimensional theoretical study of the flow and combustion of pulverized coal by diffusion flames is presented. The model predicts gas flows, species concentrations, and temperatures in combustors having specific geometries. The conservation equations are solved utilizing the κ-ε turbulence model. Coal devolatilization is modeled by the two-competing-reactions scheme, which generates two sets of volatiles and char, each by a specific rate constant, described in Arrhenius form. Char combustion from devolatilization occurs by reaction with oxygen, carbon dioxide, water, particle dispersion, and radiative heat transfer between furnace wall and particles. The model is used to investigate the interaction between flow and combustion in flames produced by arranging the locations of the primary inlet and the secondary air inlets in a furnace. The predictions, which could be valuable for designing furnaces, indicate that a centered primary inlet and a minimum recirculation are some of the criteria that could favorable for combustion.     

管道双车在不同车间距下车间螺旋流轴向速度特性研究

为进一步研究筒装料管道水力输送技术,了解管道双车在不同车间距下车间螺旋流速度特性,得出管道双车的最优运行间距。采用模型试验、理论分析相结合的方法,研究了双车间距分别为10、30、50、70、90cm情况下管道双车间螺旋流轴向速度特性。试验采用两个相同型号的管道车模型在水平光滑的有机玻璃圆管内完成,流量恒定控制为30m~3/h。结果表明,间距为10、30cm时,水流紊动混掺强烈,圆管周围间隔120°存在三个速度极大值区域,而圆管中心为速度极小值区域;间距为50、70cm时,圆管周围已无明显的涡形区域,圆管中心区域速度梯度较小,水流相对比较稳定;间距为90cm时,水流稳定,与无管道车时满管水流断面流速分布类似。由此得出,管道双车的合理间距为50~70cm。     

燃烧器角度对W型火焰锅炉空气动力场的影响研究

对配备直流缝隙式燃烧器的法国Stein公司360MW机组的W型火焰锅炉进行了冷态模型的空气动力特性研究。利用热线风速仪测量改变燃烧器角度前后炉内的流场速度，得出了不同工况下炉内W型气流的流场图，并对不同工况下的流场气流速度分布规律、炉内气流的充满度、气流行程、炉膛出口处的气流速度偏差等进行了分析，研究了炉内空气动力场的特性和变化规律。     

Three dimensional numerical modeling of simultaneous heat and moisture transfer in a moist object subjected to convective drying

The drying behavior of a moist object subjected to convective drying is analyzed numerically by solving heat and moisture transfer equations. A 3-D numerical model is developed for the prediction of transient temperature and moisture distribution in a rectangular shaped moist object during the convective drying process. The heat transfer coefficients at the surfaces of the moist object are calculated with an in-house computational fluid dynamics (CFD) code. The mass transfer coefficients are then obtained from the analogy between the thermal and concentration boundary layer. Both these transfer coefficients are used for the convective boundary conditions while solving the simultaneous heat and mass transfer governing equations for the moist object. The finite volume method (FVM) with fully implicit scheme is used for discretization of the transient heat and moisture transfer governing equations. The coupling between the CFD and simultaneous heat and moisture transfer model is assumed to be one way. The effect of velocity and temperature of the drying air on the moist object are analyzed. The optimized drying time is predicted for different air inlet velocity, temperature and moisture content. The drying rate can be increased by increasing the air flow velocity. Approximately, 40% of drying time is saved while increasing the air temperature from 313 to 353 K. The importance of the inclusion of variable surface transfer coefficients with the heat and mass transfer model is justified.     

基于OpenFOAM的旋转管道螺旋流水力特性数值研究

为进一步深入研究旋转管道产生的螺旋流对流场水力特性的影响,基于开源软件OpenFOAM,构建了水箱-管道出流气液两相流数值计算模型,模拟了竖直管、55°和45°螺旋管三种情况下的水流运动过程,通过分析、比较选定断面处速度分布、断面平均压强、湍动能随时间及空间位置的变化,总结了螺旋流对水平管段水力特性的影响。结果表明,相较于直管道,两组螺旋管道使水平管段螺旋流湍动能明显减小,压强变化趋于平缓不易产生负压,且管道内断面流速分布更加均匀。     

考虑动态摩阻的管道内水气耦合瞬变流的数值模拟

输水管道系统中经常会发生水气耦合瞬变流,可能会引起异常压力波动,甚至造成爆管事故。目前针对水气耦合瞬变流的研究很少考虑动态摩阻的影响,往往会低估瞬变过程能量衰减。对此,引入一种高效准确的简化加权类动态摩阻模型,建立考虑动态摩阻的水气耦合瞬变流模型。同时,采用虚拟塞法避免了特征线法在水气交界面的动态追踪时数值插值和求解的复杂。对比分析该模型计算结果与不考虑动态摩阻模型计算结果、试验数据,发现考虑动态摩阻的模型能更好地预测气团压力衰减和耗散,与试验压力峰值更为接近;入口压力越大,初始气团越小,动态摩阻对压力波动衰减的影响越大。     

共轨柴油机不同喷孔形式对燃油喷雾及燃烧特性的影响

采用CFD软件,基于欧拉法和拉格朗日离散法分别模拟喷油器内部流动及喷射特性,并将喷射计算结果导入燃烧模型实现联合仿真。仿真计算不同喷孔形式的喷射特性,得到了其内部速度、压力、气相体积分数(空穴)及喷雾场。仿真结果表明:在相同轨压下,小孔径喷孔油滴速度较大、贯穿距长、喷雾锥角小;燃烧湍流动能大,且较多soot打在气缸盖上,影响柴油机的可靠性。     

Effect of operating parameters on sulphur capture in a pressurized circulating fluidized bed combustor

Experiments are conducted to investigate the effect of system pressure, Ca/S ratio and primary air velocity on sulphur capture in a pressurized circulating fluidized bed (PCFB) combustor. The pressure inside the PCFB combustor is varied from 200 to 700 kPa. The Ca/S ratio is varied from 1.6 to 3.0. The primary air velocity ranges from 3 to 7 ms^?1. The bed temperature is maintained at 750°C. The sulphur capture increases with system pressure in the present range of experimental investigations. The sulphur capture also increases with Ca/S ratio up to a certain ratio and then shows a decreasing trend for the given operating conditions. A semi‐empirical model is developed for explaining the sulphur capture mechanism in the pressurized circulating fluidized bed combustor under batch combustion conditions. The experimental data are validated with the model predictions and a reasonable agreement has been observed. Copyright © 2002 John Wiley & Sons, Ltd.     

模拟贯穿裂纹内高速气液两相流动特性研究

压力管道和容器发生贯穿泄漏会引发严重的事故,合理估算贯穿泄漏量具有重要的工程意义。本文以矩形狭缝通道模拟贯穿裂纹,开展了高压氩气-水贯穿模拟裂纹的高速流动可视化试验研究,狭缝长度为20mm,间隙宽度为0.08-0.18mm。试验进口压力大于5000kPa,液体的表观速度区间为0.05-58.62m/s,气体表观速度区间为1.71-34.27m/s,采用两侧进水中间进气的特殊入口方式,研究了非均匀混合流体通过狭缝通道的流动特性。研究表明：入口压力越大出口位置压降的加速效应越明显;气体在并行双入口下,流体入口存在明显不对称流动现象,狭缝内高速气液流两相滑速比差异较小;依据本文的试验数据对两相摩擦压降的计算模型进行了验证和评价,采用Sun-Mishima关系式时对泄漏流量的估算效果最好,均相模型也具有较好的计算精度;当狭缝宽度为0.08mm时,现有关系式估算泄漏量偏小。     

泵站压力出水箱涵隔墩开孔优化研究

堤后式排涝泵站多采用压力出水箱涵作为其出水结构,多机组泵站的压力箱涵常做成汇水结构,通道数一般少于机组数,致使箱涵内各通道和其出口流速分布不均,易形成不良流态。结合物理模型试验采用CFX软件进行数值模拟,并通过在压力出水箱涵内隔墩上开孔的措施来改善压力出水箱涵内及其出口水流流态。结果表明,在压力出水箱涵内隔墩上开孔能均匀分配各通道流量,有效减小箱涵出口处流速不均匀度,改善出口流态,防止箱涵出口河床被冲刷,提高泵站安全稳定性。如将开孔处与水流垂直接触面制作成流线型结构有利于开孔处水流的平稳流动,减小开孔处水流流动产生的水头损失。     

Analysis of unsteady reacting flows and impact of chemistry description in Large Eddy Simulations of side-dump ramjet combustors

Among all the undesired phenomena observed in ramjet combustors, combustion instabilities are of foremost importance and predicting them using Large Eddy Simulation (LES) is an active research field. While acoustics are naturally captured by compressible LES provided that the proper boundary conditions are applied, combustion/chemistry modelling remains a critical issue and its impact on numerical predictions must still be assessed for complex applications. To do so, two different ramjet LES’s are compared here. The first simulation is based on a standard one-step chemistry known to over-estimate the laminar flame speed in fuel rich conditions. The second simulation uses the same scheme but introduces a correction of reaction rates for rich flames to match a detailed mechanism provided by Peters (1993) [1]. Even though the two chemical schemes are very similar and very few points burn in rich regimes, distinct limit-cycles are obtained with LES depending on which scheme is used. Results obtained with the standard one-step chemistry exhibit high frequency self-sustained oscillations. Multiple flame fronts are stabilized in the vicinity of the shear layer developing at the exit of the air inlets. When compared to the experiment, the fitted one-step scheme yields better predictions than the standard scheme. With the fitted scheme, the flame is detached from the air inlets and stabilizes in the regions identified in the experiment (Ristori et al. (2005) [2], Heid and Ristori (2003) [3], Heid and Ristori (2005) [4], Ristori et al. (1999) [5]). LES and experiments exhibit all main low-frequency modes including the first longitudinal acoustic mode. The high frequencies excited with the standard scheme are damped with the fitted scheme. The chemical scheme is found, for this ramjet burner, to have a strong impact on the predicted stability: approximate chemical schemes even in a limited range of equivalence ratio can lead to the occurence of non-physical combustion oscillations.     

Mathematical Model for Predicting the Heat Transfer Characteristics of a Helical-Coiled,Crimped, Spiral,Finned-Tube Heat Exchanger

This paper is a continuation of the authors’ previous work. Theoretical and experimental studies of the heat transfer characteristics of a helical-coiled, crimped, spiral, finned-tube heat exchanger in dry surface conditions are presented. The test section is a helical-coiled, finned-tube heat exchanger. The coil unit is composed of four concentric helical-coiled tubes of different diameters. All tubes are constructed by bending straight copper tube into seven layers of helical coil. Aluminum crimped spiral fins, with an outer diameter of 28.25 mm and a thickness of 0.5 mm, are connected around the tube. Hot water is used as a working fluid for the tube side, while ambient air is used for the shell side. The test runs are done at air mass flow rates ranging between 0.04 and 0.13 kg/s. The water mass flow rates are between 0.2 and 0.4 kg/s. The water temperatures are between 40 and 50°C. A mathematical model is developed and the simulation results show reasonable agreement with the experimental data.