Modeling and experimental validation on pressure drop in a reverse-flow cyclone separator at high inlet solid loading

High inlet solid loading is one of the most important features of cyclone separators in high density circulating fluidized beds (CFB). In this work, the effect of high solid loading on pressure drop in a reverse-flow cyclone was experimentally studied. The particles used were sand and γ-Al₂O₃. An extended range of inlet solid loadings (M), up to 30 kg of solids/ kg of air was tested at different inlet air velocities (V _in=16∼24 m/s), well beyond the solid loading range reported before. The experiments showed that, in the tested range of solid loadings, the cyclone pressure drop decreased dramatically with increasing solid loading when M<7.5 kg/kg and then almost remained constant. A new semi-empirical model for predicting cyclone pressure drop was also developed. The calculated and experimental results showed good agreement for particle free flow and particle laden flow.     

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.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20 mm,间隙宽度为80～180 μm.狭缝进口压力大于5 MPa,液体的表观速度为0.05～58.62 m/s,气体表观速度为1.71～34...     

进口压力对涡流管冷却特性影响的实验研究

为了解决燃气轮机高温部件热防护问题,采用实验研究涡流管在不同进口压力（0.20~0.65 MPa）和冷气流率（0.17~0.89）下的冷却特性。实验结果表明：实际温降,在不同进口压力下随着冷气流率的增加先增大后减小,在相同冷气流率下随着进口压力的增大而增大;温度〖JP2〗效率,在不同进口压力下随着冷气流率的增大先增大后减小,在冷气流率等于0.5时达到最大值;绝热效率,在进口压力等于0.20 MPa时最小,在大于0.30 MPa时随着进口压力的增加变化不大;制冷效率,随冷气流率的增加会先增加后减小,进口压力等于0.30和0.40 MPa时制冷效率最高。     

氦气透平压气机组合弹性环密封试验研究

氦气透平压气机采用间冷回热方式的闭式循环,因此高低压压气机以及涡轮进排气口处的密封与外层压力壳间就形成了不同压力的腔室,针对其各不同温度和压力的腔室采用组合弹性环密封.为验证组合弹性环的密封效果,设计了密封试验器和与机组上的组合弹性环完全一致的密封试验件,并在密封试验台上分别采用氦气工质和空气工质进行了试验对比.试验结果表明,组合弹性环具有良好的密封效果,在低压压气机出口进口、高压压气机出口进口以及高压压气机出口涡轮出口3处密封的泄漏分别占设计流量的0.0322‰、0.1035‰、0.1282‰,与空气介质相比,当封前压力为0.6～1.0 MPa时,氦气的泄漏约为空气泄漏的2倍,当封前压力较低时(0.1～0.2 MPa),氦气与空气的泄漏比较接近.     

煤基化学链燃烧串行流化床的冷态试验研究

采用“湍动床＋快速床”作为煤基化学链燃烧（CLC）系统的空气反应器（AR）,鼓泡床作为燃料反应器（FR）,设计了流动密封阀和旋风分离器,分别用于隔绝2个反应器之间的气氛和进行气固分离,在冷态试验装置上分析研究了CLC系统的压力分布、固体循环流量、气体泄漏率及煤灰与循环载体的分离效果．结果表明：该串行流化床反应器之间气氛隔绝性良好,气体泄漏率较低,固体循环流量达到甚至超过设计标准,FR二级旋风分离器的分离效率接近100％,FR中煤灰进入AR的质量分数小于1．55％,煤灰分离效果良好;装置可以长时间连续稳定运行,且操作气速范围较广,自行设计建造的循环流化床作为煤基化学链燃烧试验装置是可行的．     

低气压下平直翅片管换热器空气侧刘易斯因子的实验研究

在高空低气压环境模拟舱内对平直翅片管换热器的传热传质特性进行了实验,研究了不同环境压力下刘易斯因子的变化规律和影响因素,并引入了压力修正因子用来预测不同环境压力下的刘易斯因子。实验结果表明:当环境压力从101.3 kPa下降到40 kPa,刘易斯因子变化显著,最大降幅为22.2%,最大增幅为53.7%;当换热器翅片表面为部分湿工况时,入口空气含湿量对刘易斯因子影响较大,全湿工况下入口空气含湿量影响不明显;随环境压力的下降,翅片表面发生部分湿工况到全湿工况的转变,转变前刘易斯因子随环境压力下降而减小,转变后刘易斯因子随环境压力的下降而增大;引入压力修正因子后关联式能较好地预测不同环境压力下刘易斯因子,关联式和99%实验数据点的相对误差在±20%以内。     

Experimental Investigation of Heat Transfer and Resistance Characteristics of a Finned Oval-Tube Heat Exchanger With Different Air Inlet Angles

The air inlet flow direction is not orthogonal to the heat exchanger surface in many cases. To study the performance of the heat transfer and pressure drop of a heat exchanger with different air inlet angles, this paper shows the experimental system about a finned oval-tube heat exchanger inclined toward the air incoming flow direction. The heat transfer and pressure drop characteristics of four air inlet angles (90°, 60°, 45°, and 30°) are studied separately for the Reynolds number ranging from 1300 to 13000 in this study. The experimental correlations of Nusselt number and resistance coefficient of the air side are acquired. The results show that the overall heat transfer coefficients become smaller and smaller with the decrease of the air inlet angles, while the pressure drops have significant changes. The heat transfer performances of the heat exchanger under the three inclined air inlet angles are worse than that at 90°. Among the three inclined angles, the performance at 45° is the best under identical mass flow rate criterion and at low Reynolds number under identical pressure drop criterion; that at 60° is the best at large Reynolds under identical pressure drop criterion. Finally, some conclusions are attained about the effects of the air inlet angles on the heat transfer and pressure drop performance of the finned oval-tube heat exchanger.     

Pressure drop and collection efficiency of cyclone and impact separators in a CFB

Experimental results of pressure drop and gas–solid separation of impact separators with three rows of impact blades with included angles (60°, 90° or 120°) in a cold CFB set‐up of 102 mm×102 mm cross section are presented for two different samples of sand and they are compared with the same of a conventional reverse flow cyclone. The pressure drop increases with higher superficial velocity for all the solid separators including cyclone at a constant solid circulation rate. ‘Overall collection efficiency’ (η_oc) remains practically unaltered for the cyclone within the range of superficial velocity of the experiment while it decreases with higher superficial velocity for the impact separators. ‘Fractional collection efficiency’ (η_fc) of cyclone increases monotonically with grain size while that of the impact separator becomes minimum for an intermediate grain size. The collection efficiency of impact separator is comparable to that of cyclone for either very small or very large particles. Copyright © 1999 John Wiley & Sons, Ltd.     

基于火积耗散热阻的新型板式省煤器传热分析

建立了新型板式省煤器的传热模型,计算了新型板式省煤器的火积耗散热阻以及空气侧压降,分析了新型板式省煤器结构参数及空气流速变化时,火积耗散热阻及空气侧压降的变化情况。研究结果表明:增大长轴可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,并且空气侧压降变化幅度不大;增大短轴可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,但空气侧压降增大;减小板束间距可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,但空气侧压降增大,尤其是在板束间距小于20 mm时,继续减小板束间距会造成空气侧压降急剧增大;增大空气进口流速可以减小火积耗散热阻,有利于提高板式省煤器的传热性能,但空气侧压降增大,对换热器的磨损也会增加。     

Fuel cell cathode air filters: Methodologies for design and optimization

Proton exchange membrane (PEM) fuel cells experience performance degradation, such as reduction in efficiency and life, as a result of poisoning of platinum catalysts by airborne contaminants. Research on these contaminant effects suggests that the best possible solution to allowing fuel cells to operate in contaminated environments is by filtration of the harmful contaminants from the cathode air. A cathode air filter design methodology was created that connects properties of cathode air stream, filter design options, and filter footprint, to a set of adsorptive filter parameters that must be optimized to efficiently operate the fuel cell. Filter optimization requires a study of the trade off between two causal factors of power loss: first, a reduction in power production due to poisoning of the platinum catalyst by chemical contaminants and second, an increase in power requirements to operate the air compressor with a larger pressure drop from additional contaminant filtration. The design methodology was successfully applied to a 1.2 kW fuel cell using a programmable algorithm and predictions were made about the relationships between inlet concentration, breakthrough time, filter design, pressure drop, and compressor power requirements.     

1000 MW机组超超临界锅炉燃用高硫煤性能试验研究

对陕西能源赵石畔煤电有限公司的一台1000 MW超超临界机组锅炉进行了性能试验研究,分析了燃用高硫煤时锅炉在高、低负荷运行下,对锅炉效率、锅炉最大连续出力、空气预热器漏风率、汽水系统压降、空气预热器进出口烟风压降、NOx排放的质量浓度的影响.结果表明:在100％额定负荷、75％额定负荷和50％额定负荷下,锅炉效率均达到...     

径向热管换热器壳程压降数值模拟及参数优化

通过对径向热管换热器壳程压力场的数值模拟,分析入口烟气速度对换热器压降的影响规律,并对换热器结构参数进行优化。结果表明:换热器迎风侧压力高于背风侧压力,沿烟气流动方向压力逐渐降低且呈线性分布;换热器压降随入口烟气速度的增加而增加,且其增加速率也相应增大。通过改变换热器结构参数,对换热器壳程压降进行分析研究,得到其结构优化参数:翅片高度小于26.5mm,翅片间距大于6.5mm,热管横向间距108～111mm,纵向间距120～125mm。     

Frosting of heat pump with heat recovery facility

This paper aims to prolong the heat pump frost time and reduce its growth with heat recovery facility, which should mix the exhausted indoor and outdoor air before entering the evaporator. An ideal mathematic model is developed for heat transfer, frost generation and airside pressure drop. The properties of the mixture would be obtained by solving the mass and energy conservation equations. A parametric analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass flow rate on total heat transfer coefficient, frost thickness and airside pressure drop, respectively. The results show that rationalizing the ratio of indoor and outdoor air could prolong frosting time and reduce the frost thickness greatly. The total heat transfer coefficient, frost thickness and airside pressure drop increase monotonically with time going, but are not proportional. Decreasing the mixture inlet air temperature and relative humidity could essentially reduce frost growth on the tube surfaces. This can also be observed when increasing the air mass flow rate.     

Numerical investigation of pressure drop characteristics of gas channels and U and Z type manifolds of a PEM fuel cell stack

Fluid flow manifold plays a significant role in the performance of a fuel cell stack because it affects the pressure drop, reactants distribution uniformity and flow losses, significantly. In this study, the flow distribution and the pressure drop in the gas channels including the inlet and outlet manifolds, with U- and Z-type arrangements, of a 10-cell PEM fuel cell stack are analyzed at anode and cathode sides and the effects of inlet reactant stoichiometry and manifold hydraulic diameter on the pressure drop are investigated. Furthermore, the effect of relative humidity of oxidants on the pressure drop of cathode are investigated. The results indicate that increase of the manifold hydraulic diameter leads to decrease of the pressure drop and a more uniform flow distribution at the cathode side when air is used as oxidant while utilization of humidified oxidant results in increase of pressure drop. It is demonstrated that for the inlet stoichiometry of 2 and U type manifold arrangement when the relative humidity increases from 25% to 75%, the pressure drop increases by 60.12% and 116.14% for oxygen and air, respectively. It is concluded that there is not a significant difference in pressure drop of U- and Z-type arrangements when oxygen is used as oxidant. When air is used as oxidant, the effect of manifold type arrangement is more significant than other cases, and increase of the stoichiometry ratio from 1.25 to 2.5 leads to increase of pressure drop by 527.3%.     

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。     

填料式饱和器稳态和动态特性的试验研究

对填料式饱和器进行了稳态及动态特性试验研究,分析了进水流量、进气流量、进水温度对空气加热加湿过程的影响,主要考察了出水温度、出气温度、进出口空气含湿量差、填料段压降和持液量等性能参数的变化规律.结果表明：在相同进水流量下,提高水气比和进水温度,可显著提高加热加湿性能;当气相速度升高时,进出口空气含湿量差减小,填料段压降及持液量升高;在动态工况下,当进口参数发生扰动时,持液量及出水温度比压降需要更长的时间才能达到新的稳定点.     

The effect of elevated inlet air temperature and relative humidity on cogeneration system

The effect of elevated inlet air temperature and relative humidity on a gas turbine (GT) cogeneration system performance was investigated. The analysis was carried out on a GT of a capacity 171 MW at ISO condition, which is integrated with a dual pressure heat recovery steam generator (HRSG), the cogeneration system had been tested under Kuwait summer climate conditions. A computational model was developed and solved using engineering equation solver professional package to investigate the performance of a dual pressure GT‐HRSG system. The suggested HRSG is capable of producing high‐pressure superheated steam at 150 bar and 510°C to operate a power generation steam turbine cycle, and a medium pressure saturated steam at 15 bar to run a thermal vapor compression (TVC) desalination system. In this research, the influence of elevated inlet air temperature and relative humidity on the energy assessment of the suggested cogeneration system was thoroughly investigated. Results indicated that operating GT under elevated values of inlet air temperatures is characterized by low values of net power and thermal efficiency. At elevated inlet air temperatures, increasing relative humidity has a small positive impact on GT cycle net power and thermal efficiency. Integrating the GT with HRSG to generate steam for power generation and process heat tends to increase energy utilization factor of the system at elevated inlet air temperatures. Increasing inlet air temperature plays a negative impact on power to heat ratio (PHR), while relative humidity has no effect on PHR. Copyright © 2009 John Wiley & Sons, Ltd.     

Estimation of the radial distribution of the tangential velocity in a vortex chamber

The estimation of maximum tangential velocity becomes a very important factor for the estimation of performances of the vortex chamber. In this paper, a proposed flow model of how to estimate the maximum tangential velocity in the special form of the vortex chamber is described in detail. The pressure drop basing upon the rapid expansion by flowing from the inlet pipe into the cyclone body is estimated as half of the dynamic pressure in the inlet pipe.     

Thermal cycle stability of Al2O3-based compressive seals for planar intermediate temperature solid oxide fuel cells

Al₂O₃-based compressive seals were fabricated by tape casting with Al₂O₃ and 0-30 wt% aluminum powders, and their sealing effectiveness, thermal cycle stability between 200 and 750 °C and applicability in planar intermediate temperature solid oxide fuel cells were evaluated. The results indicate that increasing the aluminum content from 0 to 30 wt% in the seals decreases the leakage rate and increases the thermal cycle stability under various inlet gas (N₂) pressures of 3.5, 7.0 and 10.5 kPa. Especially, with the seal containing 30 wt% of aluminum (ACS3), the initial leakage rate was below 0.03 sccm cm⁻¹ under an inlet pressure of 10.5 kPa, and the leakage rates during 96 thermal cycles were below 0.04 sccm cm⁻¹ under the same inlet gas pressure. The interfaces in the interconnect/seal/cell assembly with the ACS3 seal retained integrity after 50 thermal cycles, demonstrating the applicability of the Al₂O₃-based compressive seals in the planar intermediate temperature SOFCs.     

Prediction of local heat transfer characteristics of dilute gas‐solid flows through an adiabatic,horizontal pipe

The local heat transfer characteristics of gas‐solid flows through an adiabatic, horizontal pipe are numerically studied using the two‐fluid model of Ansys Fluent 15. First, the model is validated with the experimental results available in the literature for the air temperature and average Nusselt number. Then, the local heat transfer characteristics of gas‐solid flows, such as temperature profiles of gas and solid, gas‐solid Nusselt number, logarithmic mean temperature difference, and effectiveness of gas and solid, are studied by changing different parameters (gas velocities 15‐24 m/s; inlet solid loading ratios 0.1‐1; particle diameters 100‐400 µm). It is observed that increasing the particle diameter and inlet gas velocity increases the gas temperature and decreases the solid temperature, increases the logarithmic mean temperature difference, and decreases the thermal effectiveness of gas and solid. However, increasing the solid loading ratio decreases the gas and solid temperatures, decreases the logarithmic mean temperature difference, and increases the thermal effectiveness of gas and decreases the thermal effectiveness of solid. Moreover, increasing the particle diameter decreases the gas‐solid Nusselt number, whereas increasing the solid loading ratio and inlet gas velocity increase the gas‐solid Nusselt number.