测湿探针加热段管壁温度及水滴汽化长度计算

建立了一维数学模型对两种加热方法加热管内流动蒸汽的加热效果进行了研究，分别计算出在均匀壁面热流密度下管壁的温度场以及恒定壁面温度条件下管壁的热流密度场，得到了不同条件下水滴的气化长度，并进行了实验验证，计算结果与实验数据相符，为测探针的设计提供了可靠的依据。     

DSG槽式聚光器吸热管壁稳态温度分布的数值研究

在DSG槽式太阳能聚光器运行过程中,吸热管外表面的热流分布不均易导致吸热管损坏,将严重影响系统的安全。文章以实际辐照为边界热流条件,对集热器吸热管两相区和干蒸汽区截面上的温度分布规律进行了二维数值研究。在稳态条件下,分析了管内不同压强、工质温度和流型对管壁温度场分布的影响。结果表明:压强和温度对干蒸汽区管壁最大周向温差无明显影响,压强较高时两相区管壁温度场分布更均匀;管内为层流时,管壁温度场分布比管内为环流时更不均匀,且整体温度更高。     

太阳能集热管内熔盐流动传热特性数值模拟

建立太阳能集热管物理模型,采用RNG κ-ε模型,基于CFD方法在不同热流边界条件下熔盐入口温度300℃,速度0.6~3.6 m/s,平均热流密度180 k W/m2参数范围内,对外径20 mm,壁厚2 mm的集热管内熔盐传热特性进行数值模拟研究。分析了集热管管壁温度分布规律和熔盐传热性能,对比了不同热流边界下管壁周向温度不均匀分布特性。研究结果表明:不同热流条件下集热管管壁温度分布规律差异较大,管内熔盐温度也存在较大差异;集热管内Nu随Re增大而升高,周向热流分布对Nu影响较大;非均匀热流边界下集热管壁温周向分布不均匀,周向热流越不均匀,壁面温差越大。     

叶片蒸汽冷却耦合换热特性的数值研究

为评估透平叶片的蒸汽冷却效果,以Mark II叶片为对象,采用热流固耦合的数值计算方法,通过与实验数据进行比较考察了不同湍流模型对计算结果的影响,对比分析了空气、过热蒸汽和湿蒸汽冷却效果的差异,研究了冷却蒸汽质量流量、进口湍动度和叶片表面粗糙度对蒸汽冷却效率的影响.结果表明:SST转捩湍流模型对于流动换热计算有较高的精度;与空气冷却相比,过热蒸汽冷却的效率更高,叶片壁面温度更低;与过热蒸汽冷却相比,湿蒸汽的冷却效率更高,叶片壁面温度更低,且随着蒸汽湿度的增加,冷却效率提高,叶片壁面温度降低;增加冷却蒸汽的质量流量可使冷却效率提高,但冷却蒸汽的温升减小;当湍流强度小于3%时,冷却效率随冷却蒸汽进口湍流强度的增大而提高;增加叶片粗糙度使得叶片冷却效率显著提高.     

蒸汽侧氧化膜对超临界机组T92钢管壁温的影响

通过建立T92钢受热管及其蒸汽侧氧化膜的数值分析模型,定量分析了不同厚度氧化膜对T92钢受热管壁温的影响,并在此基础上得出了不同受热条件下导致T92钢管超温运行的氧化膜的临界厚度值.结果表明:随着氧化膜厚度的增加,管壁平均温度和平均温度升高幅度均呈近似线性增加;且管内壁温度越高、管外热流密度越大,氧化膜的临界厚度值越小.因此,当T92钢应用于高温受热面时,需综合考虑壁面热负荷和管内壁温度对氧化膜临界厚度的影响.     

300MW循环流化床锅炉热流密度分布计算

本文采用有限元分析计算方法对宝丽华300MW循环流化床锅炉水冷壁模型的热传导分布规律进行了系列计算。分析总结出了炉外侧的管壁鳍片间的温差同管内工质与管内壁面、床侧与炉内侧金属壁面间换热系数及床内热流密度间的变化规律,为间接测量床内热流密度的分布提供了基础数据。通过测量炉外侧金属壁温并结合数值计算结果来反推无法直接测量的床内热流密度分布规律的方法具有较高的可性度和工程应用价值。     

蒙特卡洛法求二维矩形散射性介质内的辐射传递

引入辐射传递因子RDij的概念，由于该因子与温度的关系较小，因此可以将蒙特卡洛法模拟与温度场的迭代求解分开来进行。建立任意几何形状条件下蒙特卡洛法求解辐射传递因子的计算模型，并对二维矩形黑体及灰体壁面条件下的纯散射灰介质内辐射传递问题进行了模拟计算。其中，黑体壁面计算结果与文献[5,6]的结果吻合较好。另外，计算了二维矩形灰体壁面、灰体吸收散射性介质内的温度场及壁面热流分布，其结果可以供比较参考。     

太阳能烟囱强化自然通风实验研究

实验探讨了高2000mm,长1000mm的竖直集热板屋顶式太阳能烟囱模型,在改变宽度及热流密度的情况下,研究其诱导的空气量及内部空间气流温度场和速度场的变化.结果表明,在研究范围内自然通风量随烟囱宽度、热流密度的增加而增大,气流速度随热流密度的增加而增大,随烟囱宽度的增加而降低.气流温度及速度在烟囱热壁近壁面处高于其在远离壁面处,在热壁近壁处形成了温度和速度边界层.     

600MW超临界锅炉机组螺旋管圈水冷壁管壁温度

超临界锅炉水冷壁尤其是燃烧器区水冷壁的温度场计算对水冷壁的安全运行有重要意义。本文采用分区段热力计算方法计算了向火侧的热流密度。依据水冷壁入口和出口工质的实际温度和压力确定了管内工质温度及管内的对流换热系数。基于有限元法对某电厂600MW发电机组锅炉在100％BMCR工况条件下螺旋管圈水冷壁温度场进行了分析计算。     

水平螺旋槽管壁面二元混合液体升膜形成的试验研究

对二元液体混合物在蒸发状态下水平螺旋槽管管外壁面形成升膜进行了试验研究．实测了水平螺旋槽管壁面二元混合液体升膜的速度场和表面温度场,分析了水平螺旋槽管壁面热流密度和流体性质对壁面液膜特性的影响。结果表明：同一升膜工质,螺旋槽管的热流密度越大．液膜的爬升速度越大;流体性质对升膜的流动特性和温度分布特性有显著的影响,酒精溶液的浓度越高．液膜的流动性越好,表面总体温度越低,换热系数越小。     

循环流化床锅炉膜式水冷壁管与鳍片上的温度分布

研究了循环流化床锅炉膜式水冷壁管的传热，并通过采用二维传热分析方法，讨论了带有竖直鳍片和横向鳍片的水冷壁管上温度与热流分布。探讨了炉膛侧传热系数、水冷壁管水侧传热系数、水温、床温、水冷壁管材的导热率以及竖直鳍片部最高，然后逐渐下降，但在横向鳍处理的根部又会上升。为了验证传热分析的真实性，在1台6MWth循环流化床锅炉膜式水冷壁管的横裁面内安置了0.8mm的热电偶，测量子水管横截面上的一些点的温度。实际测量值符合得相当好。     

电加热倾斜管温度场分布计算

考虑自然对流对倾斜上升管内流体传热的影响,将外壁温度与外壁热负荷作为边界条件,同时将内热源作为并联网格电阻放热来进行处理,为电加热倾斜管温度场分布建立二维数学模型。根据空间节点推进的控制容积差分法求解流体换热和管壁导热耦合决定的电加热倾斜管二维温度场导热反问题,编制计算程序,针对我国第一台超临界锅炉螺旋管圈水冷壁的管型进行了管壁温度场的计算。在亚临界及超临界压力工况下,计算结果都可以很好地反映倾斜管壁温的分布规律,同时计算收敛性良好。     

Real‐time thermal states monitoring of absorber tube for parabolic trough solar collector with non‐uniform solar flux

With the world energy shortage problem becoming increasingly prominent, more and more attentions have been paid to the development of renewable energies. Among these sources, solar energy has received extensive attention with its excellent characteristics. The thermal state affects the safety of the solar heat collection system. In this paper, real‐time monitoring of the input heat flux on the inside wall and the temperature field simultaneously of an absorber tube for parabolic trough solar collector were studied. Based on the measured temperatures on the outside wall, the fuzzy adaptive Kalman filter coupled with weighted recursive least squares algorithm (WRLSA) was employed to monitor the heat states of the absorber tube inversely, in which WRLSA was used to acquire the heat flux while fuzzy adaptive Kalman filter was adopted to monitor the temperature field. The method showed strong robustness to resist the ill‐posedness. Accurate monitoring results also can be acquired when there are random disturbances of the heat transfer condition on the inner wall.     

Enhanced Boiling Heat Transfer of Water/Salt Mixtures in the Restricted Space of the Compact Tube Bundle

In desalinization devices and some heat exchangers making use of low-quality heat energy, both the wall temperature and the heat flux of the heated tubes are generally quite low, hence cannot cause boiling in flooded-type tube bundle evaporators with a large tube spacing. But when the tube spacing is quite small, incipient boiling can occur in the restricted space and results in higher heat transfer than that in a falling-film evaporator or during pool boiling at the same heat flux. This study experimentally investigates the effects of the tube spacing, the positions of tubes, and the salt-water concentration on bundle boiling heat transfer of salt water in the restricted space of the compact tube bundle evaporator under atmospheric pressure. The experimental results provide a restricted space boiling database for salt water in the compact tube bundle. Of particular importance is information concerning the influences of the tube spacing of the tube bundle and the concentration of salt water in desalination evaporators.     

Coupled Heat Transfer Simulation of the Spiral Water Wall in a Double Reheat Ultra-supercritical Boiler

This paper presented a coupled heat transfer model combining the combustion in the furnace and the ultra-supercritical(USC) heat transfer in the water wall tubes. The thermal analysis of the spiral water wall in a 1000 MW double reheat USC boiler was conducted by the coupled heat transfer simulations. The simulation results show that there are two peak heat flux regions on each wall of spiral water wall, where the primary combustion zone and burnt-out zone locate respectively. In the full load condition, the maximal heat flux of the primary combustion zone is close to 500 kW/m~2, which is higher than that in the conventional single reheat USC boilers. The heat flux along the furnace width presents a parabolic shape that the values in the furnace center are much higher than that in the corner regions. The distribution of water wall temperature has a perfect accordance with the heat flux distribution of the parabolic shape curves, which can illustrate the distribution of water wall temperature is mainly determined by heat flux on the water wall. The maximal water wall temperature occurs at the middle width of furnace wall and approaches 530°C, which can be allowed by the metal material of water wall tube 12Cr1MoVG. In the primary combustion zone, the wall temperatures in half load are almost close to the values in 75% load condition, caused by the heat transfer deterioration of the subcritical pressure fluid under the high heat flux condition. The simulation results in this study are beneficial to the better design and operational optimization for the double reheat USC boilers.     

高温太阳能吸热管在非均匀热流下的温度研究及结构优化

对腔式管状集热器在非均匀受热条件下进行温度场和热应力场的模拟.研究发现周向温差的不同造成吸热管的热变形分布不同,且吸热管后半段热变形最大;同时,太阳能辐射量随时间变化导致热流密度和吸热管壁面上的周向温差都在发生变化.鉴于此,分别从腔式集热器吸热管的结构、工作介质物性等方面入手以解决非均匀热流带来的形变问题.通过改变吸热...     

Heat Transfer Performance of an Edge-Shaped Finned Tube

The third-generation heat transfer technologies, such as three-dimensional fin and dimple, are still important means of improving energy efficiency and will continue to be challenging issues. This paper presents condensation heat transfer performance of an edge-shaped finned tube fabricated by a ploughing–extruding process. The edge-shaped finned tube integrates more than one heat transfer enhancement technology and can enhance the heat transfer capacity greatly. It is seen that the overall heat transfer coefficient and heat flux increase with inlet velocity of cold water increasing, and decrease with inlet temperature of cold water increasing, whereas the shell-side heat transfer coefficient decreases with inlet velocity of cold water increasing and increases with inlet temperature of cold water increasing. At the same inlet velocity, the shell-side heat transfer coefficient for the edge-shaped finned tube is improved by 5–7 times compared to that of a smooth tube. At the same temperature difference between wall and vapor, the shell-side heat transfer coefficient is also higher than what had been reported in the literature. The shell-side heat transfer coefficient of the edge-shaped finned tube decreases with the increase of fabrication parameter feed at the same inlet velocity or inlet temperature of cold water.     

A general analytical solution to the equation of transient forced convection with fully developed flow

A general solution to the energy equation under zero wall temperature or zero heat flux boundary condition for the decay of an inlet and initial temperature distribution of an incompressible transient turbulent flow heat transfer between two parallel plates is given. It is shown that these solutions may then be used to obtain solutions due to unit steps in wall temperature or wall heat flux which is sufficient to sort out prescribed wall temperature and prescribed wall heat flux boundary condition. The results are confirmed experimentally by the frequency method. An experimental apparatus has been designed, built and used for this purpose.     

Fouling in a Steam Cracker Convection Section Part 2: Coupled Tube Bank Simulation using an Improved Hybrid CFD-1D Model

Abstract

Performing an adequate fouling study for the heat exchangers in the convection section of a steam cracker requires reliable data on circumferential tube wall temperature profiles. A hybrid Computational Fluid Dynamics (CFD)-1D convection section model, developed to perform coupled flue gas/process gas side simulations of convection sections, is improved by the implementation of flue gas radiation modeling and extended to include typical tube banks. A complete naphtha cracker convection section is simulated with the improved hybrid CFD-1D model. All tubes show distinct maximum heat fluxes on the tube walls due to the high flue gas velocity. Based on the calculated circumferential heat flux profiles, the maximum heat flux value is calculated to be 1.8 times the average tube heat flux value. As computational costs associated with a hybrid CFD-1D simulation are high, a convective heat flux profile reconstruction scheme is developed. Using the scheme, circumferential heat flux profiles are reconstructed, based on the heat fluxes calculated when performing a fully 1D coupled convection section simulation. The heat flux reconstruction profile scheme enables fast retrieval of circumferential heat flux profiles and, thus, tube wall temperature profiles. Optimization and/or design of a steam cracker convection section becomes less computationally demanding.     

水平管降膜蒸发器传热传质实验研究

水平管降膜蒸发器因传质传热系数高而被广泛应用于淡化水处理中。搭建了水平管降膜蒸发传热实验台,通过对实验结果的归纳,得到了水平管降膜蒸发器的蒸发量随喷淋密度、蒸发温度、热通量的变化规律及热量利用率随蒸发温度的变化规律。结果表明,热通量范围不同时,蒸发量随喷淋密度的变化规律不同;蒸发量随热通量的增大而增大,随蒸发温度的增大而增大;热量利用率随蒸发温度的增大而增大。