∏形锅炉转弯烟道内的烟气流场变化及其对对流管束传热影响的分析与烟道结构改进

∏形布置的水管锅炉,后部转弯烟道内的烟气偏流会带来对流受热面的传热和温度偏差。当偏差较大时,会影响锅炉的整体运行性能。以一台70 MW热水锅炉为例,为减小转弯烟道内受热面的传热和温度偏差,结合流场数值分析调整烟道形状和尺寸,以确定合理的结构改进方案。方案实施后,经运行监测,对流管束前后部的温度偏差由17℃降低到3℃,其他相关的运行参数也都接近于设计值,取得了预期效果。     

抛物跟踪式太阳高温集热器的研究

对单轴跟踪太阳聚集系统（ＰＴＣ）进行了光学分析。对集热管内流体的混合对流（强迫对流加自然对流）和传热过程进行了探讨。理论模拟结果与实验结果吻合较好,两者间的最大偏差小于８％。     

电站锅炉对流过热器和再热器的同片热偏差

近年来,在我国400吨/时和1000吨/时锅炉的现场试验中,发现对流过热器和高、低温对流再热器均存在不同程度的同片各管间的热偏差。在有些锅炉中的高温对流过热器和再热器同屏各管间的受热长度和流量偏差虽然都很小,但仅仅由于吸热方面的偏差都使同片各管的热偏差高达1.3～1.4,造成了局部管子超温。本文综述了试验结果,对造成同片热偏差的主要原因作了理论上的分析,提出了计算方法,并提出了减小同片热偏差的设计结构方案。     

电站锅炉对流过热器和再热器壁温数值计算方法的研究

对电站锅炉对流过热器和再热器的壁温计算方法进行了改进。将各管组、管段离散化为小单元,按工质流动顺序逐次计算小单元的辐射及对流传热关系,进而求出壁温分布。采用炉膛出口二维烟温分布,从基本的热平衡关系式入手,详尽考虑了影响管子传热的结构、位置、流动等偏差因素。该计算方法符合数值计算的特点,因此便于在计算机上实现快速准确的壁温计算。图７表１参８     

大容量锅炉烟侧热力偏差和攻关研究成效

锅炉现有多种燃烧方式，都会发生燃烧产物的能量不平衡，影响工质吸热均匀性。切圆旋转燃烧在未消除残余旋转时，引起对流烟道两侧较大烟温偏差，当与工质吸热偏差迭加后增大热偏差，甚至发生再热器起温爆管。通过多年试验研究，查明了起因，找到了改善措施，经多台锅炉实炉改进后验证试验，取得较好成效，现已总结经验推广应用。     

发展大容量超临界参数锅炉的几个问题

发展大容量超临界参数锅炉已提到议事日程,本文对炉膛和燃烧系统,对流受热面汽温偏差,超临界参数等方面的问题进行分析探讨,提出了一些建议。     

用模化试验结果推算锅炉水平烟道宽度方向汽温偏差的方法

烟道内空气动力场的严重偏斜会引起对流受热面沿烟道宽度各片的出口汽温产生很大偏差,并可能导致受热面的局部超温爆管.本文提出了用炉内模化试验结果推算对流过热器和对流再热器沿烟造宽度各片出口汽温偏差的一种方法.图5参4     

对流过热器与再热器的汽温偏差对烟温偏差的敏感性研究

在大型电站锅炉中,烟道内烟温偏差是影响过热器与再热器系统汽温偏差的主要因素之一,因而在设计与运行过程中颇受关注。该文从理论上建立了对流过热器和再热器的出口汽温偏差与其进口烟温偏差之间的关系,据此分析了汽温偏差对烟温偏差的敏感性以及减小过热吕与再热器系统汽温偏差的措施。     

湿烟气在开孔翅片管外凝结换热数值模拟

为高效回收湿烟气全热并对烟气冷凝换热设备进行优化设计,以设计的紧凑式开孔翅片管换热器为对象,采用欧拉壁膜(EWF)模型与组分输运模型耦合研究低温烟气在翅片管换热器中的凝结换热规律。数值模拟得到的凝结速率及对流凝结换热系数与实验结果最大偏差分别为13.4%和10.9%。结果表明：对流凝结换热系数随入口水蒸气质量分数和烟气流速增大以及管壁温降低而增大,翅片开孔可以起到均压、破坏温度边界层、截断液膜、加快凝结液排出进而强化传热的作用,基于模拟拟合的关于改进雅各布数J的烟气对流凝结关联式与实验数据平均相对误差为13.1%,模拟关联式对于90%的实验结果预测误差在-20%～+20%以内。     

低熔点熔融盐管内强迫对流换热的实验研究

利用课题组自行配制的二元混合熔融盐(KNO3-Ca(NO3)2)开展导热油与低熔点熔融盐的管内强制对流实验研究。通过实验得到导热油与低熔点熔融盐的总换热系数,并通过最小二乘法和Wilson分离法得到了管内低熔点熔融盐侧的对流换热系数及其准则关联式。与不同的经典传热关联式对比,最大偏差为+23%。考虑高温熔融盐的变物性特征,利用黏度项对Dittus-Boelter方程关联式进行修正。经过修正后的Dittus-Boelter方程与实验测试结果最大偏差为-15%,偏差值明显减小。过渡流实验数据和Hausen方程及Gnielinski方程的最大偏差均为10%,实验结果验证了传热关系式仍适用于高温熔融盐的结论。     

1000MW超超临界锅炉水冷壁壁温计算

采用分区计算简化大容量高参数超超临界锅炉炉内辐射、对流传热模型,研究炉膛水冷壁热负荷及壁温的空间分布情况,并与试验数据进行了对比,计算结果与试验值之间的偏差较小,最大为5.72%.该模型与算法可给出不同锅炉负荷条件下,水冷壁壁面热负荷与壁温沿炉膛宽度方向的分布规律.结果表明,水冷壁热负荷与壁温均呈现出中间高两端低的弧形分布.四角切圆燃烧锅炉火焰位置对炉内传热有很大影响.模拟计算可为超超临界锅炉的运行提供参考,预测了在材料允许温度范围内,火焰中心偏斜最大不超过2 m.     

Experimental study on the heat transfer characteristics of fluoride salt in the new conceptual passive heat removal system of molten salt reactor

A new conceptual design of a passive residual heat removal system (PRHRS) has been proposed for molten salt reactor. High‐temperature heat pipes are used in this new design to improve the system inherent safety and make the PRHRS more compact. An experimental system using fluoride salt FLiNaK has been constructed to validate and support the future design of PRHRS of molten salt reactors. In this research, tests on the natural convection heat transfer of FLiNaK in the drain tank with an inclined heat pipe inserted at different heights were performed. The temperature distribution of fluoride salt in the tank was analyzed. The height of heat pipe and the bulk temperature of FLiNaK have little influence on the normalized salt temperature distribution. However, with the height of heat pipe increasing, the temperature difference of molten salt decreases and heat transfer coefficient of natural convection increases. In addition, the empirical correlations of natural convection heat transfer between liquid FLiNaK and inclined heat pipe are obtained within the range of Rayleigh numbers from 3.97 × 10⁶ to 1.16 × 10⁷. The comparisons show that a good agreement with less than 5% deviation is obtained between the proposed correlations and the test data.     

A Clothing Ventilation and Heat Loss Electric Circuit Model with Natural Convection for a Clothed Swinging Arm of a Walking Human

This work aims to develop a computationally effective electric circuit model to estimate the ventilation and heat transfer for walking human in the presence of natural convection. The ventilation circuit includes flow resistance, inductance, and electromotive force elements. It is coupled to an electric resistance circuit of heat flows to adjust the temperature difference inducing natural convection flow. The coupled ventilation and heat circuit models predicted both the segmental ventilation rate and heat loss from the arm at different walking and wind speeds. The developed model of the segmental ventilation and heat transfer from the clothed human segment was validated by performing experiments on a walking thermal manikin using tracer gas method. Good agreement was observed between the model predictions and the experiment at a maximum relative error of 10% lying within the standard deviation range. Results showed that the simplified ventilation-heat circuit models succeeded in estimating the natural convection effect at low computational cost. Moreover, it was shown that the effect of natural convection is more significant in walking at no wind than in windy condition. Accounting for natural convection effect increases the segmental ventilation and heat loss at low air permeability (0.02 m/s) by 68% and 20%, respectively.     

Natural convection heat transfer from a horizontal cylinder using holographic interferometry

The natural convection heat transfer from a horizontal cylinder with a uniform wall temperature in an infinite space was experimentally investigated. Infinite fringe interferograms of the cylinder heated from 295.15 to 355.15 K were recorded using the holographic interferometry technique. The temperature field around the cylinder was reconstructed based on phase difference recovery using a MATLAB code. The distributions of the local and average Nusselt numbers over the cylinder were then obtained. A correlation of the average Nusselt number was proposed for a Rayleigh number range of 2.7–6.0 × 10⁴. The experimental results are in good agreement with previous correlations, with a deviation of ±10%. The holographic interferometry technique was found to be satisfactory and reliable for heat transfer analyses.     

Effects of viscous dissipation on fully developed forced convection in porous media

An analytical study on fully developed forced convection in a homogeneous porous medium is presented. Closed form solutions for the temperature distributions in the transverse direction with the inclusion of frictional heating due to viscous dissipation are obtained, with variations of Darcy number and Brinkman number. The frictional heating effect on the temperature distributions is investigated and analyzed for both heating and cooling processes. Variations of Nusselt number as a function of Darcy number and Brinkman number are examined, and the deviations of the Nusselt numbers with that of the model without incorporating the effect of frictional heating are presented in a contour deviation map for a more holistic comparison.     

Analysis of distributed thermal management policy for energy-efficient processing of materials by natural convection

Natural convection is the governing phenomena in many material processing applications. The conventional method of uniform heating at the bottom wall of an enclosure may result in inadequate thermal mixing and poor temperature distribution leading energy wastage. In this work, an alternative, energy-efficient method of distributed heating of the cavity is studied and compared with the isothermal bottom wall heating case in enhancing the thermal mixing and improving the temperature distribution in the cavity. Steady laminar natural convection of various fluids of industrial importance (Pr = 0.015, 07, 10, 1000) in the range of Ra = 10³–10⁵ is studied in a differentially heated cavity and in two cases of discretely heated square cavities. Detailed analysis is carried out by visualizing the heat flow by heatlines. The thermal mixing and temperature uniformity in each case are quantified in terms of cup-mixing temperature and root-mean square deviation (RMSD), respectively. It is found that thermal management policy of distributed heating significantly influences the thermal mixing and temperature uniformity in the enclosures. In a case with multiple discrete heat sources, a remarkable uniformity in temperature across the cavity is achieved with moderate thermal mixing.     

On the intrinsic transient capability and limitations of solid oxide fuel cell systems

The intrinsic transient performance capability and limitation of integrated solid oxide fuel cell (SOFC) systems is evaluated based on the system balance-of-plant response and fuel cell operating requirements (i.e., allowable deviation from nominal operation). Specifically, non-dimensional relations are derived from conservation principles that quantify the maximum instantaneous current increase that a solid oxide fuel cell system can safely manage based on (1) the desired fuel cell operating point, (2) the maximum allowable fuel utilization, (3) the maximum average fuel cell temperature deviation, (4) the response delay and (5) the operating requirements of the system balance-of-plant components. New non-dimensional numbers representing the ratio of species or thermal convection to volumetric capacitance in the fuel cell during balance-of-plant delay have been developed.