计算刷式汽封泄漏流动的多孔介质模型

通过对刷式密封刷丝束中泄漏流动特点的分析,把刷丝束当作多孔介质来处理,有效简化刷丝束中复杂的泄漏流动,建立了刷丝束中多孔介质的泄漏流动模型。刷式密封内泄漏流动的特性采用的是基于多孔介质模型Reynolds-averaged Navier-Stokes方程的数值计算方法进行研究的。计算和分析了不同转速、不同压差和不同孔隙率下的泄漏流量。计算结果表明:在相同的孔隙率下,压差越大泄漏量越大;在相同的压差下,孔隙率越小,泄漏量越小;刷式密封的泄漏量与轴的转速无关。通过数值计算和实验结果的对比,两者数据吻合较好,验证了采用多孔介质模型模拟刷式密封刷丝束的可行性。     

相变微胶囊功能流体相变区间的影响因素和变化趋势分析

相变微胶囊功能流体所具有的相变区间是影响其强化传热效应和工程应用价值的主要因素。采用双流体数学模型通过数值模拟发现:在层流条件下,双流体模型能够很好地模拟颗粒相体积分数、管径和R e对相变区间的影响。功能流体的相变段长度和总吸热量都随着这三个因素的增大而显著增大。同时相变段长度还取决于入口温度和边界条件等因素。以直链烷烃为相变材料的功能流体在相变段的蓄热能力相近。但在同R e下,功能流体的相变段长度和总吸热量都随着囊芯材料相变温度的升高而减小。入口温度是影响相变材料熔化速度的重要因素。相变段的长度、总温升和总吸热量与流体入口过冷度都呈线性关系。在第一类边界条件下,相变段长度与壁面过热度呈指数为负的幂指数关系,而相变段总温升和总吸热量都随壁面过热度的增大而增大。     

LPG站集合管内空化现象分析

液化石油气(LPG)从集合管流入各个支管时由于局部压力的变化会产生空化现象,生成大量气泡。当气泡溃灭时将引发强烈的冲击波和高速微射流,形成气蚀极易对管线造成损害。针对液化石油气通过各个支管空化的影响因素进行数值计算,结果表明:入口压力越高,空化数越小,气含率越高,湍动能越大。当改变出口压力时发现,出口压力越高,空化数越大,气含率越低,湍动能就越小。随着管径的增大,空化强度越高,空化数越小,气含率越高,湍动能越大。     

Counter-Rotating Type Tidal Stream Power Unit Boarded on Pillar （Perform- ances and Flow Conditions of Tandem Propellers）

The authors have invented the unique counter-rotating type tidal stream power unit composed of the tandem pro- peUers and the double rotational armature type peculiar generator without the traditional stator. The front and the rear propellers counter-drive the inner and the outer armatures of the peculiar generator, respectively. The unit has the fixftful advantages that not only the output is sufficiently higher without supplementary equipment such as a gearbox, but also the rotational moment hardly act on the pillar because the rotational torque of both propel- lers/armatures are counter-balanced in the unit. This paper discusses experimentally the performances of the power unit and the effects of the propeller rotation on the sea surface. The axial force acting on the pillar in- creases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Be- sides, the force vertical to the stream also acts on the pillar, which is induced from the Karman vortex street and the dominant frequencies appear owing to the front and the rear propeller rotations. The propeller rotating in close to the sea surface brings the abnormal wave and the amplitude increases as the stream velocity is faster and/or the drag is stronger.     

工业燃气轮机进气室设计参数对压气机进气均匀性影响的数值研究

为了降低径向进气室对压气机通流性能的影响,通过三维数值仿真对进气室的设计参数进行了研究。首先,量化评价了不同的进气室平直段子午型线对压气机进气均匀性的影响,然后对进气室支板与平直段支撑筋之间的相对角度进行了研究。研究结果表明：压气机的通流裕度对进气室平直段的型线较为敏感,需要谨慎修型以确保通流性能不会衰减;进气室平直段型线的改型主要诱发压气机进口径向叶尖的旋流畸变;而进气室支板与平直段支撑筋之间相对角度的改变对压气机进口的周向叶根畸变略有影响,支板与支撑筋重合会导致进气室的压损增加,压气机的喘振裕度略有下降,建议支板与支撑筋错开一定角度。     

管道末端水击压力计算及误区分析

引水系统的管道参数不同会导致管道末端水击压力波动形态差异较大,在工程仿真计算时得到的管道末端压力变化曲线难以校验。为得到管道末端压力波动曲线,首先结合经典的水击分类图,分析了引用传统水击计算方法时存在的误区。其次,从水击经典理论中的阀门端压力升高方程组出发,推导出各相水击压力升高值的通用形式,得到管道末端水压的简化计算公式,公式表明管道末端阀门开度是影响管道末端水压变化形态的重要因素。最后,利用数值仿真验证所提计算方法的可行性。结果表明,提出的管道末端水压简化计算方法与特征线法得到的压力变化曲线相似度较高,且表现出水压波动形态在管道末端阀门不同初始开度下的变化规律,方法简单实用。     

Power and efficiency optimization for combined Brayton and inverse Brayton cycles

A thermodynamic model for open combined Brayton and inverse Brayton cycles is established considering the pressure drops of the working fluid along the flow processes and the size constraints of the real power plant using finite time thermodynamics in this paper. There are 11 flow resistances encountered by the gas stream for the combined Brayton and inverse Brayton cycles. Four of these, the friction through the blades and vanes of the compressors and the turbines, are related to the isentropic efficiencies. The remaining flow resistances are always present because of the changes in flow cross-section at the compressor inlet of the top cycle, combustion inlet and outlet, turbine outlet of the top cycle, turbine outlet of the bottom cycle, heat exchanger inlet, and compressor inlet of the bottom cycle. These resistances control the air flow rate and the net power output. The relative pressure drops associated with the flow through various cross-sectional areas are derived as functions of the compressor inlet relative pressure drop of the top cycle. The analytical formulae about the relations between power output, thermal conversion efficiency, and the compressor pressure ratio of the top cycle are derived with the 11 pressure drop losses in the intake, compression, combustion, expansion, and flow process in the piping, the heat transfer loss to the ambient, the irreversible compression and expansion losses in the compressors and the turbines, and the irreversible combustion loss in the combustion chamber. The performance of the model cycle is optimized by adjusting the compressor inlet pressure of the bottom cycle, the air mass flow rate and the distribution of pressure losses along the flow path. It is shown that the power output has a maximum with respect to the compressor inlet pressure of the bottom cycle, the air mass flow rate or any of the overall pressure drops, and the maximized power output has an additional maximum with respect to the compressor pressure ratio of the top cycle. When the optimization is performed with the constraints of a fixed fuel flow rate and the power plant size, the power output and efficiency can be maximized again by properly allocating the fixed overall flow area among the compressor inlet of the top cycle and the turbine outlet of the bottom cycle.     

飞灰复燃对炉内颗粒沉积状况的影响分析

实际工程表明,采用飞灰复燃技术对锅炉进行改造,可以减少飞灰所带走的燃料损失,提高锅炉效率,但飞灰回收复燃给壁面颗粒沉积状况也带来了影响.采用FLUENT模拟了SZL15-1.25-AⅡ型双筒链条蒸汽锅炉炉内燃烧,对比分析了采用飞灰复燃技术前后炉内壁面颗粒沉积状况.模拟结果表明,飞灰复燃对锅炉顶墙、前墙及后墙的颗粒沉积速率影响较大,其中飞灰复燃提高了顶墙和前墙的颗粒沉积速率,降低了后墙颗粒沉积速率,而对锅炉前后拱的影响很小可以忽略.减小飞灰入射质量流量或调整飞灰入射角度为水平偏下,均可以降低颗粒在水冷壁的沉积速率,有利于炉膛与水冷壁间的传热.     

多孔介质太阳能吸热器性能分析

采用4种多孔骨架中辐射传输模型,包括:忽略多孔骨架内部辐射模型(模型A)、Rosseland模型(模型B)、均匀内热源模型(模型C)与吸热器中辐射传输满足Beer定律的模型(模型D),推导得到了局部非热平衡条件下4种模型所对应的吸热器中多孔骨架温度、空气温度和吸热器热效率的解析解,分析了多孔骨架孔隙率、导热系数和孔隙直径对吸热器性能的影响。结果表明,对模型A和模型B,吸热器中最高温度位于吸热器进口处;对模型C,吸热器中最高温度位于吸热器出口处;而在模型D中,吸热器中吸热器内部或吸热器的出口处温度最高。吸热器效率取决于多孔骨架导热系数、孔隙率和孔隙直径等参数,当吸热器中内热源均匀分布时,吸热器效率是最高的。     

基于仿生学的风力机塔架结构设计及其力学性能分析

风力机塔架力学结构属典型的柔性细长弹性体,考虑到沿海一带棕榈树与近海风力机结构(同为细长柱体)所处环境的相似性,以传统筒型和仿生风力机塔架为研究对象,通过棕榈树样本参数拟合出树干外形函数,并考虑棕榈树内部维管束结构及其材料特性,分别建立了刚性、柔性和布置类维管束结构的仿生塔架3种塔架模型,进一步采用有限元方法对3种塔架进行静力学分析、模态分析与谐响应分析,并对比3种塔架的力学性能,分析仿生结构对塔架力学性能的影响。结果表明:风载荷作用下,原始塔架的最大应力主要集中在塔架底部,仿生塔架则集中在塔架底部以上;与柔性塔架相比,仿生塔架顶端位移增加了282.0%,而最大应力仅增加了18.0%,在满足塔架应力允许范围内,仿生塔架柔性更好;仿生塔架达到共振时塔顶位移响应幅值降低了22.2%,且共振频率点均偏大;与刚性塔架相比,柔性与仿生塔架的固有频率均较低,而仿生塔架的固有频率略高于柔性塔架。     

Y型喷嘴内部气液两相流动及液膜雾化的数学模型

根据前人实验观察结果所得的流动结构,从气液两相各的质量,动量、能量平衡及其相互作用方程的构造入手,包括混合孔内油流端部界上的正应力传递,两相平行界面上的剪应力作功传热等,建立了Ｙ型喷嘴内部流动过程的数学模型,进而,依据不稳定表面波理论及空气动力破碎理论,分别对Ｙ型喷嘴出口油膜的初级破碎及二次雾化过程作了进一步的模化,建立了一套较为完整的Ｙ型喷嘴性能预测及设计优化的数学方法,经检验,实际使用效果良好     

不同环状缝隙宽度下管道车车后断面轴向流速特性研究

管道车车后流场作为柱系绕流流场的一部分,尾迹绕流可能会对管道车柱系结构产生影响,进而影响管道车柱系结构稳定性。为此分析了4个不同缝隙宽度下管道车车后断面的轴向流速特性。结果表明,车后断面轴向流速受管道车结构影响呈区域性分布;距离管道车一定时,环状缝隙越小,相同断面轴向速度变化幅度越剧烈;管道车车后轴向流速变化幅度沿程减小,管道车对水流的影响沿程衰减,速度大小沿程向断面平均流速靠拢。     

Operation analysis of a photovoltaic lighting system with battery and heater

An operation analysis is presented for a photovoltaic system consisting of the photovoltaic generator, the battery, the light, and the heater. An optimal resistive load for lighting is determined according to the characteristics of the battery. The working domain of the battery is marked out to display the range of the battery charge supplied by the photovoltaic generator. Before sunrise and after sunset, the battery supplies power to the light with an optimal resistive load. When the sun is above the horizon but sunset or not sunrise for the tilled photovoltaic module, the system is at rest. If the beam radiation is really incident on the surface of the module and induces a characteristic inside the working domain, all power will charge the battery. Once the characteristic is outside of the working domain, the resistive load is chosen to balance the currents of photovoltaic generator, battery charge, and heater. It is the only situation of concurrence. If the open-circuit voltage of the photovoltaic array under insolation is less than the zero-current voltage of the battery at the fractional state of charge, or if the battery is at full charge, the battery is disconnected from the photovoltaic system and the power output of the photovoltaic array to the heater is found by the method of maximum power point tracking.     

不同相对厚度前缘缝翼对S809翼型气动性能的影响

文章通过数值模拟方法研究了不同相对厚度的前缘缝翼对S809翼型气动性能的影响,并揭示了前缘缝翼相对厚度对流动控制产生影响的机理。研究结果表明:在大攻角下,空气流经过前缘缝翼会在其尾部产生涡旋,尾缘涡旋的形成有助于抑制S809翼型流动分离,进而改善翼型绕流场;不同相对厚度的前缘缝翼产生尾缘涡旋不同的流动轨迹,对翼型的流动控制作用效果不同;相同条件下,前缘安装最大相对厚度为35%的前缘缝翼能够将S809翼型最大升力系数提升至1.25,失速攻角推迟至17.21°;安装最大相对厚度为14%的前缘缝翼,能够使S809翼型最大升力系数提升至1.53,并使翼型在攻角为20.16°时仍未发生失速。     

颗粒组合角度对近壁颗粒传热特性的影响

为了探究颗粒堆积结构变化对近壁面颗粒传热过程的影响,构建了近壁面两颗粒的非稳态传热模型,研究了不同初始温度条件下颗粒组合角度变化对近壁面颗粒传热特性的影响规律。结果表明：初始温度越高,所需换热时间越长,颗粒组合角度增加,使得换热时间明显减少。初始温度为1073K时,换热面平均热流密度值呈先迅速下降后缓慢下降的趋势。同一时刻,组合角度越大,颗粒平均温度越低。不同组合角度颗粒的固相传热率均达到0.8以上。颗粒组合角度越大,固相传热占比越小,辐射传热占比越大。在换热前期,辐射传热率最高可达0.57,对传热过程的影响不可忽略。     

Effect of the cathode gas diffusion layer on the water transport behavior and the performance of passive direct methanol fuel cells operating with neat methanol

The passive operation of a direct methanol fuel cell with neat methanol requires the water that is produced at the cathode to diffuse through the membrane to the anode to compensate the methanol oxidation reaction (MOR). Hence, the anode performance of this type of fuel cell can be limited by the water transport rate from the cathode to the anode. In this work we theoretically show that the water transport from the cathode to the anode depends primarily on the design of the cathode gas diffusion layer (GDL). We investigate experimentally the effects of the design parameters of the cathode GDL, including the PTFE (polytetrafluoroethylene) content in the backing layer (BL), and the carbon loading and the PTFE content in the microporous layer (MPL) on the water transport and the performance of the passive DMFC with the help of a reference electrode. The results indicate that on one hand, these parameters can be adjusted to decrease the water concentration loss of the anode performance, but on the other hand, they can also cause an increase in the oxygen concentration loss of the cathode performance. Hence, an optimal balance in minimizing the both concentration losses is the key to maximize the cell performance.     

背压微增条件下汽轮机出力的简化计算

为获得准确的背压微增条件下汽轮机出力特性,分析背压变化时机组热力系统变工况实际运行特性,基于对热力系统的合理假设和相关经验公式的应用,在忽略汽轮机本体结构和内部级组热力参数变化的前提下,提出了汽轮机背压微增出力特性的简化计算方法。以某300 MW湿冷机组和660 MW间冷机组的变背压工况性能试验数据为例进行验证,结果表明,简化计算获得的微增出力特性曲线的斜率和试验结果偏差在3%以内,是一种行之有效的背压微增出力特性高精度计算方法。     

Thermodynamic analysis of waste heat power generation system

In the present work, a waste heat power generation system is analyzed based on the criteria with and without considering the heat/exergy loss to the environment. For the criteria without considering the heat/exergy loss to the environment, the first- and second-law efficiencies display different tendencies with the variations of some system parameters. When the heat/exergy loss to the environment is taken into consideration, the first and second law efficiencies display the same tendency. Thus, choosing the appropriate expressions for the performance criteria is crucial for the optimization design of the waste heat power generation system. It is found that there are two approaches to improving the system performance: one is to improve the heat/exergy input; the other is to enhance the heat-work conversion ability of the system. The former would deteriorate the environment if the heat-work conversion ability of the system remains unchanged; the latter could reduce the environmental impact but it’s restricted by the heat/exergy input. Therefore, the optimal operation condition should be achieved at the trade-off between the heat/exergy input and the heat-work conversion ability of the system.     

热网管道保温与热化发电之间的相互关系分析

热网管道的保温设计，尤其是长距离热风管道的保温设计，对热网管道设计成功与否显得十分重要。而热电厂供热参数的高低不仅与经济发电相关，更主要的是跟热网的保温、散热损失有关。一般热能工程设计手册中，仅有经济厚度等计算方法介绍，而没有考虑保温散热损失对热化发电的影响。这对集中供热来说是合理的，但对于热电联产来说，似乎有点欠缺。本文试图通过实例分析计算，来说明保温厚度、散热损失、热化发电的相互关系。以期重视热网管道的保温设计、施工，正确处理经济厚度与热化发电的联系，进一步降低消耗，节约能源。     

平面形状不规则对高桩码头地震效应的影响

为了进一步明确平面形状不规则对高桩码头地震效应的影响,以L型平面不规则高桩码头为例,基于美国Northridge地震波,采用ABAQUS有限元软件对比分析了平面形状不规则与规则高桩码头的地震反应,研究了平面形状不规则对高桩码头各桩桩顶水平力、弯矩及结构整体扭转角的影响。结果表明,高桩码头平面形状不规则会导致桩顶水平力和结构整体扭转角的增大,桩基地震破坏数目增加;平面形状不规则高桩码头转角部位桩群水平力峰值普遍较大,且应力复杂,设计中需重点考虑。