基于脉动能的微管道中气液两相流流型的识别

基于小波分析流型的识别方法一般是采用各尺度能量作为特征值,但它易受外界条件的影响.作者在微管道中两相流的研究中,重新定义了一个脉动能并以此作为特征值,结合改进的BP神经网络对流型进行识别.实验表明,采用脉动能作为特征值不易受压力绝对值的影响,在微管道中气液两相流流型的识别过程中取得了比较好的结果.     

高质量含气率垂直下降两相绕流的研究

通过热敏电阻式和压力晶体式两种实验方法对高质量含气率垂直下降气液两相流进行研究,分析了绕过梯形柱体所形成的绕流尾流流态,在高质量含气率垂直下降气液两相流中,不易形成稳定的涡街,且热敏电阻式检测器不适用来测试高质量含气率垂直下降气液两相流中的涡街。     

高质量含气率垂直下降两相绕流的研究

通过热敏电阻式和压力晶体式两种实验方法对高质量含气率垂直下降气液两相流进行研究 ,分析了绕过梯形柱体所形成的绕流尾流流态 ,研究表明 ,在高质量含气率垂直下降气液两相流中 ,不易形成稳定的涡街 ,且热敏电阻式检测器不适用来测试高质量含气率垂直下降气液两相流中的涡街 .     

一种适用于稠密液固两相湍流的新模型

为了较准确描述稠密液固两相湍流流动,在全面考虑了流体相和颗粒相的湍流脉动及单颗粒随机脉动的基础上,建立了一种新模型。利用作发展的ＤＩＰＳＡＲ算法对竖直上升管道中稠密液固两相湍流进行了数值模拟,所得结果与实验值吻合较好。     

小型制冷系统两相流致噪声研究进展

系统地回顾了制冷剂两相流致噪声研究的主要进展. 两相流理论研究表明,流致噪声的根本原因是压力降随时间的变化,流型对压力降的变化有显著影响,压力降的波动会引起管道的振动和噪声. 空泡动力学理论指出流型会影响气泡尺寸和形状,表现出声学特性的变化. 从热力学效应、管系和节流元件结构等方面出发,阐述各因素对流致噪声的影响,综合比较两相流致噪声抑制手段的效果. 从实验和数值模拟2个方面,概述了两相流致噪声研究方法的发展. 展望了两相流致噪声研究的发展方向,可以通过评价噪声特性的关键指标参数,系统地考察特征参数对流致噪声的影响,提出噪声抑制措施,未来指导制冷系统的优化设计.     

筒口气团作用下航行体垂直出筒数值研究

潜射航行体出筒过程是水下发射的基础与前提,具有受力剧烈、时间短和非线性等特点。基于CFD方法,利用VOF多相流模型追踪气液界面,结合高分辨率交界面捕捉(HRIC)与重叠网格(零间隙)技术,建立了完整描述航行体水下垂直出筒的数学模型,系统研究了筒口气团与发射参数对流场与航行体载荷特性的影响规律。结果表明：随着筒口气团初始压强的增加,航行体受力变化周期增长,筒口气团演化过程减慢;发射深度的增加有助于缩短出筒过程中筒口气团脉动周期,肩部压强增加,有利于抑制航行体自然空化;横向来流会显著增加航行体横向受力与偏转力矩;横向流作用下,筒口气团脉动过程对航行体偏转力矩与横向受力影响较大。     

非饱和带轻非水相液体污染研究进展

通过对近年来轻非水相液体在非饱和带的污染机理、毛细压力-饱和度-相对渗透系数关系以及数学模 拟的分析,总结了在三相流模拟过程中主要参数及物理过程的研究方法以及近年来研究非饱和带轻非水相液体 污染的各种数学模型,论述了各种方法的优点和不足,提出需进一步研究解决滞后现象对油分布的影响;三相同 时流动时气相对其他两相的影响;非等温条件下轻非水相液体进入包气带的污染迁移机理;开展原位实验研究 复杂条件下的轻非水相液体污染迁移问题。     

垂直井筒两相流温度场的模拟计算

井筒多相流体的物性参数和流变特性参数等均是温度的敏感函数,因此,精确计算井筒多相流体的温度分布是准确预测其压力分布、进行油井生产参数优化设计和工况分析等的重要基础。文中基于两相流动力学和传热学理论,建立了垂直井筒及其周围地层温度场的数学模型。依据建立的模型,编制了不同开采工艺下的井筒温度场计算程序,并对单相和两相流体流动下的井简温度场进行了计算与对比分析。     

管内油气两相流流量变化瞬态过程研究

为了给油气两相流管线的设计和运行的安全性提供参考依据,并为油气两相流瞬态模型研究提供检验数据,对流量改变引起的油气两相流瞬态过程进行了详细实验研究。实验系统的管路采用管径为２９ｍｍ,总长为１８ｍ的有机玻璃管道,由水平段、垂直上升段和垂直下降段三种管道布置组成;实验工质为３０＾＃机油和空气。在垂直下降段、水平段和垂直上升段设置测量段,测量压力、压降、含液率和流型;用微机数据采集系统实现自动连续采集,     

层流脉动流动对流换热数值分析

为了改进换热器设计方法及提高设备换热效率,通过建立恒定热流密度加热的圆管内层流脉动流动数学模型,对流量脉动条件下的流动与传热特性进行了数值分析.研究结果表明,脉动流动时速度与压降发生同周期的变化,但两者之间存在相位差,随着脉动频率增加,相位差逐步趋近于π/2;脉动速度的径向分布在一定频率范围内出现环状效应,频率越大速度脉动幅值越小,但环状效应越明显;温度脉动幅度随脉动频率、普朗特数增加而减小,随速度脉动幅度增加而增加.     

层流管流耦合换热对流体热边界条件的影响

通过对管外壁非均匀加热/冷却条件下层流管内受迫流动热入口段内流体与管壁间耦合传热的分析计算,研究了试件几何尺寸、试件与流体物性参数及流体流动状态对管内流体内管壁处热边界条件均匀性的影响,并就如何选择试验管段材料和尺寸以提高实验精度给出了原则性建议. 结果表明,管壁导热与管内流体间的耦合作用对内管壁处流体的热边界条件有着重要的影响. 影响流体热边界条件均匀性的主要量纲一的量是数、管壁材料的相对导热系数、实验段相对加热长度和管壁相对厚度.     

Characteristics of Convection Heat Transfer in Power-Law Fluid Saturated Porous Media Channel

幂律流体饱和多孔介质通道内对流换热特性

田兴旺¹,张琨¹,刘峰¹,王平²,徐士鸣²

（1.大连海洋大学 海洋与土木工程学院,辽宁 大连 116023;2.大连理工大学 能源与动力工程学院,辽宁 大连 116024）

摘 要：

基于Darcy-Brinkman-Forchheimer流动模型和局部非热平衡模型,考虑黏性耗散效应的影响,建立了幂律流体在多孔介质通道内流动传热的一般模型。推导出无量纲速度分布和流、固温度分布的计算表达式,并在恒热流边界条件下,利用经典的四阶Runge-Kutta法进行了自编程序的数值求解。模拟结果表明,无量纲的相间传热系数Bi、有效导热系数比k、达西数Da,布林克曼数Br、综合惯性参数F等表征参数对无量纲流、固温度分布有着较大的影响,同时发现不同幂律指数的流体对流动传热特性也有着重要的影响。

关键词：粘性耗散;幂律流体;多孔介质;局部非热平衡;数值模拟

     

海上摇晃条件下油轮货油温降规律数值模拟研究

油轮在海上运输过程中会发生旋转运动和平移运动,货油温降过程为伴随着自由液面运动的非稳态混合对流过程,水热力规律较静止情况更为复杂。基于FLUENT动网格的VOF模型对摇摆(旋转运动)条件下的原油自由液面运动规律及舱内货油温降规律进行系统研究。结果表明,摇摆一方面不断改变浮升力相对于船舱的方向,使得自然对流不断被扰动;另一方面导致自由液面与船舱内壁及舱内顶部空气间的相对运动,使静止条件下的自然对流变成强制对流。以上两方面的影响均对舱内原油与舱外海水间的传热产生了显著的强化作用,使得温降速率与旋转角速度呈正相关。     

Thermal design of a novel heat sink cooled by natural convection with phase transition in the series loop

In this paper, a novel heat sink, cooled by natural convection, with phase transition in the circulation loop was designed, and the heat sink was applied on averaging temperature and cooling the electronic equipment. The working fluid in the heat sink was driven by the capillary pump. Numerical simulations were performed, to study the heat transfer performance of two systems with various heating power, filling ratios and refrigerants. The influences of above elements on temperature uniformity of two systems were also studied and the thermal performances of two systems were compared. The volume of fluid (VOF) model was utilized to simulate fluid motion in ANSYS FLUENT. The simulation results indicate that the temperature differences of the system comprising two substrates (system 1) are very small under suitable filling ratio conditions, and the thermal performance of system 1 is preferable to the system comprising one substrate (system 2) at the same volume. Besides, the simulation results also show that the system using R245fa possesses excellent temperature uniformity for the same filling ratio and heating power. Finally, the experiments were investigated and the experimental results proved the correctness of the theoretical model.     

多孔平板复合换热的理论与实验研究

在高温流动系统中,垂直放入多孔平板可增强辐射换热效应,提高能量的利用率。本文建立了这一对流辐射复合换热系统的理论模型;对不同情况进行了数值计算,并做了实验研究;分析了入口气流温度、风速、板数和板厚等因素的影响;从而确立了这一类问题的计算模型,精确地预测了实验结果。     

New friction factor and Nusselt number equations for laminar forced convection of liquid with variable properties

Friction factor and heat transfer coefficient of liquid flow with variable properties can significantly differ from that with constant properties. Existing equations obtained by regression analysis of experimental data use correction factors to account for variable property effect. They are limited to specific kind of fluid and low or medium temperature differences. The correction factors of the equations for heating and cooling conditions are different. New explicit friction factor and Nusselt number equations for laminar forced convection of liquid with variable properties are derived with a first order approximation of dynamic viscosity-temperature variation. The new equations are applicable to all kinds of liquids and can be used for large temperature differences. Governing equations of laminar forced convection of water and ethanol are numerically solved using computational fluid dynamics(CFD)method and the results are used to verify the derived equations. The derived equations show good predictions of friction factors and Nusselt numbers for both heating and cooling conditions and show more accurate predictions than the existing equations. A dimensionless number is also introduced based on theoretical analysis to evaluate property variation effects on friction factors and heat transfer coefficients.     

Theoretical investigations on heat transfer to H_2O/CO_2 mixtures in supercritical region

The supercritical H_2O/CO_2 mixture is the working fluid to drive a turbine in a novel power generation system with coal gasified in supercritical water. This system is promising because of zero pollution emission in contrast to the conventional coal-fired power plant. Heat transfer coefficients of the supercritical H_2O/CO_2 mixtures are important to design heat transfer devices in this system, which is similar to the role of heat transfer to supercritical water in conventional systems. However, heat transfer to supercritical mixtures has received less attention. Here, we show that the supercritical mixtures with H_2O being one of the components, have similar convection heat transfer behavior to supercritical pure fluids for temperatures and pressures above the critical point of H_2O. This phenomenon was demonstrated from two aspects. Firstly, the forced convection heat transfer coefficients of supercritical mixtures were numerically calculated using the simulation model for supercritical pure fluids and using the thermophysical properties(density, heat capacity, thermal conductivity and viscosity) of supercritical mixtures as input.The calculated results agree well with experimental data in the supercritical region. Secondly, the calculated results also agree well with the correlations for supercritical pure fluids. The mechanisms were investigated by molecular dynamics simulations on the diffusion of supercritical mixtures. These results lay the foundation for predicting convection heat transfer coefficients of supercritical mixtures and for designing heat transfer devices with supercritical mixtures as heat transfer fluids.     

空冷型光伏光热一体化系统的实验研究

对空冷型单晶硅光伏光热一体化系统进行了实验研究,充分肯定了光伏光热一体化系统对于提高电效率和利用热能的作用.通过对带有风机的空冷型强制对流单晶硅电池板与空冷型自然对流单晶硅电池板两者的电效率、净电效率和热效率的比较,探讨风机对于电池板散热的效果以及对其各项效率的影响.     

新型管状相变材料热管理系统的数值仿真与实验研究

设计了一种新型的管状复合相变材料(tubular Composite PCM,t-CPCM)结构,用以替代传统的块状复合相变材料(block-shaped Composite PCM,b-CPCM)结构,将其耦合强制对流换热后应用于电池热管理。仿真结果表明,相比于b-CPCM电池仿真模型,t-CPCM电池仿真模型不仅流道分布更加均匀,而且对流换热面积更大,理论计算得出的对流换热热阻仅为0.8 K·W⁻¹,是b-CPCM电池仿真模型的1/20。实验结果表明,t-CPCM电池模组优异的散热性能可以有效地控制电池温度,t-CPCM电池模组的最高温度仅为46.9 ℃,温差为0.8 ℃;而b-CPCM电池模组的最高温度高达51 ℃,温差均为5 ℃。所设计的管状复合相变材料在电池热管理方面具有良好的应用价值。     

Modeling of dendritic growth in the presence of convection

In materials science, dendritic growth is the ubiquitous form of crystal growth ob-served in casting and welding of many metals and alloys. The solidified dendritic mor-phology will generally play a key role in the determination of mechanical properties of solid materials. Thus, understanding and control of dendritic growth are crucial in order to predict and achieve desired microstructures and hence, mechanical properties of cast-ing metals and alloys[1]. Dendritic growth is a complicated phy…