蒸汽管网的智能监测系统

利用正常蒸汽管网的实测数据作为神经网络学习样本,通过神经网络的学习不断调整通过传热理论建立的正常管网传热模型中的温度分布系数,由此建立一个逼近实际蒸汽管网模型的传热模型,并以此作为蒸汽管网的诊断系统的诊断标准.再结合数据采集系统和对管网实时运行状况模拟和故障报警系统,组成蒸汽管网的智能监测系统.最后,用VC编程实现了该系统.     

开孔金属泡沫的传热分析

主要从开孔金属泡沫微观组织的基本结构出发对开孔金属泡沫内的固体热传导、气体热传导和热辐射进行了分析,根据以上的分析利用能量方程和两热流法建立了开孔金属泡沫的传热模型,并利用试验对泡沫镍的有效导热系数进行了测量,泡沫镍的有效导热系数实验值验证了开孔金属泡沫传热模型的正确性.     

颗粒物料传热过程的数值模拟与实验研究

转筒干燥器的主体是略带倾斜并能回转的圆筒体,是一种既受高温加热又兼输送的设备,它的应用十分广泛.文中较为系统地进行了转筒干燥器物料传热过程的分析,并进行了试验研究.利用质量平衡方程、能量平衡方程和传热方程,建立了颗粒物料在转筒干燥器干燥过程中的传热数学模型,并使用有限元法进行了模拟研究,该模型能够较好地预测干燥过程中物料颗粒的温度变化,模拟结果与实验结果吻合良好.该模拟程序对此类问题的研究具有参考价值.     

线弹性土壤中埋设悬跨管道的屈曲分析

建立了两端埋设在线弹性土壤中的悬跨管道的屈曲方程。利用细长梁小挠度理论,建立了含有轴向压力的悬跨段和埋设段管道的弯曲控制方程。基于埋设段管道的刚度和变形特性,建立了符合悬跨段管道实际情况的边界条件。导出了悬跨段管道对称屈曲和反对称屈曲的屈曲载荷方程,通过数值求解给出了不同土壤刚度系数条件下悬跨段管道屈曲载荷。研究表明:悬跨段管道的屈曲载荷系数依赖于土壤刚度系数,简支梁模型只在特定的土壤刚度系数下适用于悬跨管道;在土壤刚度系数很大时,两端固支梁模型才能反映悬跨管道的屈曲特性。建议采用该方法进行埋设悬跨管道的屈曲分析。     

空调列车夏季行驶热舒适性分析

利用MATLAB／SIMULINK平台,建立了空调硬座列车的围护结构动态传热及PMV的计算模型;其中在PMV的计算中,考虑了人体散湿量、空气相对湿度及内壁温度和平均辐射温度对PMV-PPD值的影响。对空调硬座列车空调双位控制分别采用不同的反馈信号对热舒适性的影响,进行了理论上的分析。本文建立的模型,可用于列车空调相关问题的研究。     

基于有限元思想的无限微热源冶炼炉温度机理研究

对无限微热源法制备β-SiC粉体的冶炼炉进行温度机理研究,根据传热形式、传热模型推导出无限微热源冶炼炉的导热微分方程,采用Galerkin法对方程进行变分并得出平面非稳态导热温度场分布方程,利用有限元思想对方程进行推导,再采用有限差分方法求解温度矩阵以得到炉内各个时刻温度的变化情况.     

片冰机蒸发器的工程传热模型研究

对片冰机蒸发器的传热特点进行了分析,在一定简化基础上,建立了片冰机蒸发器的工程传热模型,得到了制冰时间、制冰厚度、蒸发温度、进水温度、结冰筒材料与壁厚等几个工程应用中的重要参数间的关联式。用该关联式预测的制冰时间与试验结果吻合良好,所建传热模型对片冰机的优化设计有指导意义。     

水平管道预冷过程研究

利用气液同速推进分层流动模型和涵盖预冷过程中主要传热工况的传热模型,采用有限差分法求解了甲烷液体预冷水平管道过程中管道温度的分布情况.     

基于Abaqus二次开发的天然气管道在役焊接热力耦合模拟

目的 研究直径、压力对天然气管道在役焊接温度场和径向变形的影响规律,并提高变参数分析的建模效率,减少大量重复操作。方法 以Abaqus软件为平台,利用Abaqus GUI Toolkit软件开发参数输入界面,利用Python语言编辑主程序,开发用于天然气管道在役焊接热力耦合有限元模拟的参数化插件,实现几何模型建立、材料与截面属性设置、网格划分、分析步建立、焊缝单元生死控制、边界条件施加的快速自动完成。利用所开发的参数化插件,对不同直径、压力条件下管道在役焊接的热力耦合场进行分析。结果 随着压力增加、管道直径减小,熔池及其正下方管道内壁的温度峰值逐渐降低。在管道在役焊接过程中,径向变形是主导、周向变形次之、轴向变形最小。随着管道直径的增加,压力对熔池正下方管道内壁径向变形的影响愈加显著,并且两者呈正相关。结论 所开发的参数化插件可用于管道在役焊接热力耦合分析,显著减少了变参数模拟的工作量,提高了建模效率。研究成果可为管道在役焊接模型的建立和工艺参数的优化提供参考。     

轴向力作用下埋设于线弹性土壤中的悬跨管道振动分析

利用细长梁的小挠度理论,建立了两端埋设在线弹性土壤中的含轴向力的悬跨管道自由振动方程。基于埋设段的刚度约束特性,建立了悬跨段管道的边界条件。解析求解得到了悬跨段管道频率方程,数值求解了不同土壤刚度和轴向力条件下悬跨段管道的固有频率。研究表明:悬跨段管道振动特性取决于轴向力系数和土壤刚度系数,工程上推荐使用的简支梁和两端固支梁模型只在几个特殊参数点上适用,建议采用该方法进行悬跨管道振动分析。     

On the admissibility of replacing the heat conduction equation of a pipe wall by the heat balance equation in investigating transients in heat exchangers

An expression is obtained to determine the fraction of the thermal resistance of a pipe wall which must be referred to the inner boundary when using the heat balance equation for the wall instead of the heat conduction equation (for a heat exchanger with independent heating). Limits of applicability of the model with temperature concentrated along the pipe radius are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 19, No. 6, pp. 1079–1087, December, 1970.     

Determination of surface heat-transfer coefficients of steel cylinder with phase transformation during gas quenching with high pressures

In numerical simulation of quenching process, the boundary conditions of temperature field and stress field are very important, in which the boundary conditions of temperature field are very complicated. In order to simulate the thermal strains, thermal stresses, residual stresses and microstructure of the steel during gas quenching by means of the numerical method, it is necessary to obtain an accurate boundary condition of temperature field. The surface heat-transfer coefficient is a key parameter. The explicit finite difference method, non-linear estimate method and the experimental relation between temperature and time during quenching have been used to solve the inverse problem of heat conduction. The relationships between surface temperature and surface heat-transfer coefficient of cylinder have been given. The non-linear surface heat-transfer coefficients include the coupled effects between phase transformation and temperature. In calculation, physical properties were treated as the function of temperature and volume fraction of constituent. The results obtained have been shown that this technique can determine effectual the surface heat-transfer coefficients during gas quenching.     

Numerical and experimental studies of heat and flow characteristics in a laminar pipe flow of nanofluid

Thermal performance of energy systems can be improved by adding metal or metal-oxide nanoparticles to a base fluid, thereby increasing heat-transfer efficiency. Laminar pipe flow of a Cu–water nanofluid was studied using discrete phase model numerical simulation and experimental methods. The forces including thermophoretic and Brownian forces were considered to solve the particles governing equation. A two-step method was employed in the preparation of the nanofluid. The influences of Reynolds number, fluid temperature, and particle volume fraction on the flow pressure drop and convective heat-transfer coefficient of the nanofluid have been studied. The results demonstrated that adding nanoparticles to a base fluid significantly enhanced convective heat transfer in a pipe and increased energy loss. The pressure drop increased with increasing Reynolds number. A critical nanoparticle volume fraction existed, beyond which the pressure drop changed from increasing to decreasing with increasing nanoparticle volume fraction. This is attributed to competition between slip of particles on the pipe wall and the effect of a drag force on the particles. The deposition efficiency of nanoparticle changing with the particle size and volume fraction also has been illustrated.     

热管及其主要应用领域的研究

热管是一种超导热体的传热元件,具有传热系数高、温度分布均匀、热响应迅速、结构紧凑、工作可靠等优点.本文介绍了热管的工作原理、结构,重点阐述了热管式散热器在一些领域里的应用,并作了性能的分析和研究,最后介绍了热管在电机领域里的有望广泛应用.     

An entry-flow problem for a non-isothermal catalytic-wall reactor

A reacting gas flows into a metal, thin-walled, tube which has a catalytic coating on its inner surface. A strong, temperature-dependent, exothermic reaction occurs giving a local hos spot. It is assumed that the surface temperature is controlled by heat conduction through the metal wall, heat transfer into the gas being negligible. A standard approximate technique is used to derive an integral equation which relates the mass transfer at the wall in the Blasius boundary layer to the wall temperature. A second integral equation is derived from the heat-conduction problem for the metal wall, and the coupled equations are solved numerically. The maximum temperature rise at the wall is found to be significantly higher than that obtained when a fully developed flow passes over a catalytic coating.     

Experimental study on cooling enhancement of crushed rock layer with perforated ventilation pipe under air-tight top surface

Under the warm and ice-rich nature of permafrost and the scenarios of climate warming on the Qinghai-Tibet Plateau, it will be necessary to use combinatorial techniques of cooling the ground temperature in the proposed Qinghai-Tibet Express Highway of construction. For the crushed rock highway embankment embedded a perforated ventilation pipe in permafrost regions of the Qinghai-Tibet Plateau, the mechanism of impact on the cooling capability enhanced by a perforated ventilation pipe in the air-tight crushed rock layer was studied using laboratory experiment. All boundary conditions at each edge of the crushed rock sample with dimensions of 100 × 60 × 100 cm except the inlet and outlet of the perforated pipe are air-tight. A ventilation steel pipe with an inner diameter of 8 cm was drilled with many small holes with a diameter of 1 cm and horizontally embedded in the length direction of the crushed rock sample with a depth of 53 cm. The laboratory experiments with a periodically fluctuating air temperature in the inner test tank regulated by program control were performed. The perforated pipe is only ventilated during the negative temperature fluctuation period in the inner test tank. The results show that the heat transfer processes in the crushed rock layer embedded a perforated ventilation pipe with an air-tight surface include pure heat conduction, forced convection that occurs in the crushed rock layer forming directly a pore air circulation in conjunction with the in-duct air by the small holes of perforated pipe wall absorbed from the inner test tank, and convective heat transport between the in-duct air and the inner surface of ventilation pipe wall. When air temperatures in the inner test tank are colder than the pore air temperatures in the crushed rock region around the perforated ventilation pipe, the perforated ventilation pipe can produce a significantly enhanced cooling of the crushed rock layer base due to the direct formation of a complete pore air circulation in the crushed rock layer in conjunction with the in-duct air via the small holes of the perforated pipe wall. When the fluctuating air temperature in the inner test tank rises from a minimum value to a warmer one than the pore air temperature in the crushed rock region around the perforated pipe during the negative temperature ventilating period, a warming process begins to occur in the crushed rock layer due to a warmer in-duct air absorbed from the inner test tank. This stronger warming process in the crushed rock region around the perforated pipe may decrease the cooling capability of the air-tight crushed rock layer. Thus, in order to avoid this warming process at this stage before ventilating end, the ventilating end time of ventilation pipe ought to be brought forward.     

导热相复合陶瓷微波烧结传热模式数值分析

根据微波加热的特点,采用二维稳态导热数值分析法,建立了导热相复合陶瓷微波烧结的传热模式. 研究了导热相的浓度、导热相弥散分布状况、基质类型以及保温方式对复合陶瓷内部二维稳态温度场分布的影响,并设计了导热相SiC晶须复合TZP陶瓷的微波烧结致密化实验,对建立的复合陶瓷的微波烧结传热模式进行了验证. 结果表明：导热相复合陶瓷设计时宜选取具有高导热系数的基体,保持导热相有较高的浓度,使导热相均匀分布于基体中,且微波烧结传热宜采用合适的保温设施.     

Investigation of transient conduction–radiation heat transfer in a square cavity using combination of LBM and FVM

In this paper, the effect of surface radiation in a square cavity containing an absorbing, emitting and scattering medium with four heated boundaries is investigated, numerically. Lattice Boltzmann method (LBM) is used to solve the energy equation of a transient conduction–radiation heat transfer problem and the radiative heat transfer equation is solved using finite-volume method (FVM). In this work, two different heat flux boundary conditions are considered for the east wall: a uniform and a sinusoidally varying heat flux profile. The results show that as the value of conduction–radiation decreases, the dimensionless temperature in the medium increases. Also, it is clarified that, for an arbitrary value of the conduction–radiation parameter, the temperature decreases with decreasing scattering albedo. It is observed that when the boundaries reflect more, a higher temperature is achieved in the medium and on boundaries.     

A numerical study on the heat-transfer characteristics of an array of alternating horizontal or vertical oval cross-section pipes placed in a cross stream

In this paper, a numerical study on the flow of an array of alternating horizontal or vertical oval cross-section pipes placed in a cross stream, resembling that encountered in a real cross-flow heat exchanger, is presented. The results include temperature contours and velocity vectors on the surface of the pipe and at several selected cross-sections, the local and sectional averaged Nusselt number distributions, and the overall Nusselt number variations versus the internal and external flow Reynolds numbers. The computation shows that the wall temperature varies dramatically along both the circumferential and the axial directions of the pipe, and is far different from a constant wall temperature distribution assumed in most previous studies. In general, the portion of the pipe with external wall facing forwards the cross-flow stream has lower temperature and higher local heat-transfer rate than the portion with wall facing backwards the cross-flow stream. At the maximum external flow Reynolds number, Re = 40, considered in this paper, the magnitude of pipe's overall Nusselt number is about one-sixth the magnitude of that calculated based on the ideal constant wall temperature assumption.     

Pressure-drop reduction and heat-transfer deterioration of slush nitrogen in horizontal pipe flow

Cryogenic slush fluids such as slush hydrogen and slush nitrogen are two-phase, single-component fluids containing solid particles in a liquid. Since their density and refrigerant capacity are greater than those of liquid-state fluid alone, there are high expectations for the use of slush fluids in various applications such as clean-energy fuels, spacecraft fuels for improved efficiency in transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental tests were performed using slush nitrogen to obtain the flow and heat-transfer characteristics in two different types of horizontal circular pipes with inner diameters of 10 and 15 mm. One of the primary objectives for the study was to investigate the effect of pipe diameter on the pressure-drop reduction and heat-transfer deterioration of slush nitrogen according to changes in the pipe flow velocity, solid fraction and heat flux. In the case of an inner diameter of 15 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 3.6 m/s. On the other hand, in the case of an inner diameter of 10 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 2.0 m/s. From these results, it can be seen that a larger pipe diameter produces a higher onset velocity for reducing pressure drop and deteriorating heat-transfer characteristics. Furthermore, based on observations using a high-speed video camera, it was confirmed that pressure drop was reduced and heat-transfer characteristics deteriorated when the solid particles migrated to the center of the pipe and the flow pattern of the solid particles inside the pipe was pseudo-homogeneous.