自然循环在冲击热负荷作用下的流动特性实验研究

冲击热负荷条件下的自然循环是工程中常见的汽液两相流动与传热过程 ,同时也是一个复杂的非稳态过程。转炉余热锅炉是一种典型的运行于冲击热负荷下的大型换热设备 ,冲击热负荷严重地影响着其水循环流动特性 ,从而影响它的寿命。在实验模拟氧气顶吹炼钢转炉余热锅炉的实际工作过程的基础上 ,研究了冲击热负荷、压力和初始速度等因素对不稳定传热和流动的影响。实验结果表明 ,自然循环在受到冲击热负荷后 ,水循环流量迅速达到最大值 ,呈现较快的响应速度 ,随后在最大流量附近脉动。循环流量的主要影响因素是冲击热负荷的强度 ,而压力和初始速度对循环流量的影响则较小。     

亚临界300～350MW自然循环水动力特性的计算分析综述

结合国内外锅炉生产厂家的亚临界自然循环锅炉水动力计算数据和已经运行的亚临界自然循环锅炉的运行测试数据,分析了锅筒压力和循环回路的结构特性如水冷壁管内径、循环回路的高度、下降管和引出管与上升管的截面比等对亚临界自然循环锅炉水循环特性的影响,管子内壁粗糙度、局部阻力系数、锅内旋风分离器阻力、锅筒水室凝汽率等参数在水循环计算时如何选取,水循环可靠性的评定等。     

亚临界自然循环水动力特性的分析

结合国内外锅炉生产厂家的亚临界自然循环锅炉水动力计算数据和已经运行的亚临界自然循环锅炉的运行测试数据,对锅筒压力和循环回路的结构特性如水冷壁管内径、循环回路高度、下降管和引出管与上升管的截面比等对亚临界自然循环锅炉水循环特性的影响,管子内壁粗糙度、局部阻力系数、锅内旋风分离器阻力、锅筒凝汽率等参数在水循环计算时的选取,...     

变压运行直流锅炉水冷壁中间集箱汽液分配特性的试验研究

利用空气-水试验回路,模拟了超临界变压运行直流锅炉在35%、50%和75%额定负荷(ECR)下汽-液两相流在中间集箱中的分配特性.采用快关阀门法和摩擦阻力法分别测量了各支管内的体积含气率和流量分布.试验结果表明:在入口干度x=0.7~0.95的范围内,35?R下并联支管的含气率分布最均匀,随着负荷的增加,各支管间的相分配偏差增加;锅炉负荷增加时,并联支管内流量分配的均匀性增加.     

余热锅炉自然水循环计算及快速设计方法

介绍余热锅炉基本结构及自然水循环的原理,并以压差解法为例阐述了余热锅炉自然水循环安全校核计算的目的和方法。通过分析衡量自然水循环安全性的循环倍率K,提出快速计算余热锅炉有关自然水循环结构参数的方法。     

超临界循环流化床锅炉垂直并联内螺纹管内两相流不稳定性的研究

针对600 MW超临界循环流化床(CFB)锅炉水冷壁管在低质量流速条件下的水动力特性,进行了垂直并联内螺纹管内两相流不稳定性的试验研究,得到了不同条件下的水动力特性曲线和压力降、密度波2种脉动的典型脉动曲线.在试验参数范围内,分析了系统压力、质量流速、进1:2过冷度和上游可压缩容积对两相流不稳定性的影响.根据试验结果,采用均相流模型得到了不稳定发生的界限关系式,为超临界CFB锅炉垂直并联内螺纹管水冷壁的设计与安全运行提供了依据.     

自然循环高温热水锅炉的水循环试验

文章介绍了自然循环高温热水锅炉的水循环试验结果,通过水循环试验测得了角隅水冷壁管的循环流速及锅炉的循环流量,从而求得了锅炉的循环比率。通过水循环试验及计算,求得了炉膛各面墙的墙间热负荷不均匀系数,此系数与《水动力计算方法》中所推荐之值有较大的差异。文章最后介绍了锅炉突然停电试验的情况,说明了自然循环热水锅炉对于突然停电有很好的适应能力。     

超临界压力下水冷壁中间集箱分配特性的研究

研究了国产600 MW直流锅炉分配集箱水冷壁管在超临界压力下的流量分配特性。试验参数为:压力p=23~25MPa,质量流速G=400~1 200 kg/(m2.s),工质温度t=10~400℃。试验研究了工质压力、质量流速和工质温度对分配集箱垂直水冷壁管流量分配特性的影响。试验结果表明:随着质量流速的增加,垂直水冷壁管间流量分配的均匀性增加;在拟临界点附近,流量分配不均匀性有一阶跃增加,而且随着压力的增加,流量分配不均匀性在拟临界点的阶跃增加现象变弱。利用分配集箱并联支管的离散模型计算了分配集箱垂直水冷壁管内的流量分配,计算结果与试验数据吻合。     

高压自然循环干熄焦余热锅炉热力特性研究

根据干熄焦的工艺特点,参考干熄焦余热锅炉运行经验,在保证自然循环安全可靠的基础上,设计研究干熄焦余热锅炉在高压下实现自然水循环的结构布置和热量分配情况,分析研究设计所得热力特性参数,为高压自然水循环干熄焦余热锅炉的进一步设计及研发提供了设计依据.     

用引射配水管锅炉的水动力计算及现代化设计

一、研究意义由于在自然循环热水锅炉中,循环力是冷热水的密度差形成的,而这一密度差值与自然循环蒸气锅炉相比较要小的多,因而在热水锅炉自然循环水冷壁系统中介质的流速往往偏小,很容易发生过冷沸腾(表面沸腾),以致引起管内积垢不断增长为使自然循环热水锅炉的水循环情况得到进一步改善,我校在热水锅炉水动力特性实验研究的基础上,于1982年提出将回水管设置在下降管进口(如图1所示)。采用这种进水方式能够从两个方面对自然循环水冷壁管组的安全运行带来好处:     

一种用于铬盐生产中余热回收新型锅炉的设计开发

根据铬盐生产的工艺流程以及其烟气特性,设计开发出一种用于铬盐生产余热回收的新型锅炉。该型锅炉的主要特点是:受热面U型结构布置,自然循环、蒸发器三级并联布置,蒸发器采用加肋片结构,省煤器采用H型翅片管布置,蒸发器和省煤器管束呈交叉布置等。实践表明,该型锅炉对窑炉烟气温度、粉尘具有很好的适应性。     

Simple and Clear Approach to Industrial Boiler Circulation Analysis

Circulation in the industrial boiler is the continuous supply of water to the boiler heated tubes in order to sustain steady steam output without overheating tubes. Adequate circulation occurs when there is sufficient flow of water into tubes for adequate cooling. In the natural circulation industrial boiler system the rate of flow in the circulation system is governed by flow resistances and differences in density between downcomer tube circuits and heated riser circuits. Control of these resistances allows adequate flow of water to parallel circuits. Adequate water flow through the boiler's heat-absorbing circuits is necessary to cool the tubes. To insure proper boiler circulation, a simple, clear, and comprehensive approach is described in this article covering all aspects in boiler circulation analysis. The analysis details all boiler circulation circuits, explaining all forces imposed on them, including thermosyphon as well as friction forces.     

Measurement and simulation of flow rate in a water-in-glass evacuated tube solar water heater

This paper evaluates the characteristics of water-in-glass evacuated tube solar water heaters including assessment of the circulation rate through single ended tubes. A numerical model of the heat transfer and fluid flow inside a single-ended evacuated tube has been developed assuming no interaction between adjacent tubes in the collector array. Flow measurement using Particle Image Velocimetry (PIV) has been undertaken to validate the numerical model. The experimental rig consists of a single full-scale tube coupled to a storage tank. A non-dimensional correlation has been developed of the circulation rate through a single evacuated tube mounted at 45° inclination over a diffuse reflector. Simulation results show that the natural convection flow rate in the tube is high enough to disturb the tank’s stratification and that the tank temperature strongly affects the circulation flow rate through the tubes. Circumferential heat distribution was found to be an important parameter influencing the flow structure and circulation rate through the tube, hence a separate correlation needs to be developed if a concentrating reflector is incorporated into the collector.     

Effect of Two-Phase Natural Circulation Distortion on Tube Failure in Steam Boilers

Two different cases of evaporator tube ruptures in power station boilers due to natural circulation distortion are presented. The first case discussed concerns a 110-MW, unit boiler with bottom evaporation tubing inclined at 15° to the horizontal. At the high heat fluxes present in the furnace, subcooled boiling occurs in inclined tubes. For these inclinations an insufficient flow rate causes local heat transfer deficiencies due to vapor-water separation. The introduction of internally finned tubes eliminates local heat transfer deficiencies and prevents further tube failures. The second case is that of circulation interruption due to blowdown during start-up. The water level in the drum of this second 110-MW, unit boiler was controlled by inlet header blowdown during start-up. Thus, natural circulation was interrupted, causing local overheating of evaporator tubing. The event was identified by an increase of the tube rupture frequency. After changing the blowdown procedure, the interruptions of natural circulation were avoided and the tube failure frequency decreased substantially.     

Self-compensating characteristic of steam–water mixture at low mass velocity in vertical upward parallel internally ribbed tubes

This paper presents an experimental investigation on Self-Compensating Characteristic (SCC) in vertical upward parallel tubes with low mass velocity of steam–water two-phase mixture. A physical model was built up using parallel internally ribbed tubes. A method called Differential Pressure Substitute was used to measure two-phase flow parameters. The results indicated that the SCC of vertical upward parallel tubes is caused by combined action of frictional pressure drop and gravitational pressure drop. The mass velocity in the tube with lower heat flux decreases first, and then increases with an increase in quality. The uneven heat fluxes among tubes are the main reasons that cause mass velocity differentials. Greater uneven heating ratio enhances the SCC in low quality region and weakens it in high quality region. The SCC has different variation rules in different pressure region. In the sub-critical pressure region, rising pressure weakens the SCC when quality is low and enhances it when quality is high. In near-critical pressure region, the mass velocity varies monotonically and slowly with the increase in quality because the difference between water and steam is minor in this pressure region. The results provide some instructive advices to improve the design and operation safety of once-through boiler.     

The latent heat recovery from boiler exhaust flue gas using shell and corrugated tube heat exchanger: A numerical study

The excessively increasing environmental concerns along with reducing fossil fuel resources introduce the trend of increasing the efficiency of boiler via implementing waste heat recovery. In the present study, the potential of latent heat recovery is investigated in the middle‐size boiler exhaust flue gas using the shell and corrugated tube heat exchanger. The main purpose of the present study is efficiency growth in flue gases using latent heat recovery of the steam energy. The heat recovery analysis is evaluated by a validated computational fluid dynamics model by a commercial software. For this study, the effect of different tube arrangements, number of tubes, and flow direction in the shell on heat transfer and pressure drop were investigated. The results showed that in‐line arrangement of the tubes in the shell presents better thermal performance and also high pressure drop among the other arrangements. As a result, by considering the thermal performance and pressure drop, radial arrangement shows higher performance. According to the obtained results from Section 2 of the present study, by considering the radial arrangement of tubes in the shell, as the number of tube rises, the thermal performance declines.     

热敏感性对直流锅炉水冷壁安全运行的影响

根据汽液两相流动阻力的计算式,推导了流量敏感系数、出口焓值敏感系数的表达式。对直流锅炉内螺纹管、螺旋管圈水冷壁的热敏感系数进行了定量计算,分析了各种因素对热敏感性的影响,并对两种水冷壁管屏在热负荷不均时的温度偏差,焓值偏差进行了讨论,对直流锅炉安全运行具有一定的指导意义。     

管壳式废热锅炉整体强度的有限元分析

管壳式废热锅炉整体强度计算具有相当的复杂性,其中管板强度和管板与管子连接强度显得尤为关键。通过建立锅炉整体结构的有限元分析模型,更加全面且贴切地表征了管板、管子分布以及管板与管子连接的真实结构,从而更加详尽而准确地反映了废热锅炉整体的应力应变分布,为科学合理地设计及优化废热锅炉提供了理论指导。     

200MW机组电站锅炉调峰低负荷水循环安全可靠性

论述了在 2 0 0MW机组电站锅炉所作的调峰低负荷水循环安全在线监测试验。试验目的主要是检验该炉在调峰低负荷运行时水循环的可靠性。试验结果表明 :在 70 %以上电负荷运行时不会出现水循环问题 ;在 5 0 %电负荷滑压运行时水循环流速有些波动 ,但波动的最低值远大于水循环可靠性较差的循环流速界限值 ,仍有足够的流量冷却水冷壁管 ,不致于引起管壁超温 ;在 5 0 %电负荷滑压运行时不宜投水力吹灰器 ;在40 %电负荷下不宜长期运行 ;在 3 0 %电负荷下不宜运行。     

Thermal–hydraulic analysis of a steam boiler with rifled evaporating tubes

Rifled evaporating tubes are applied in the steam boilers with the aim to increase the steam–water mixture turbulization and to prevent the burnout of tubes walls. The rifled evaporating tubes and the working fluid forced circulation are applied in the steam boiler at the Thermal Power Plant “Kolubara B” that is being built by the Electric Power Utility of Serbia. In order to investigate operating characteristics of the steam boiler of such an advanced design, a simulation and analysis of complex coupled thermal processes on the furnace gas side and thermal–hydraulics inside the evaporating tubes were performed for the whole range of plant operating loads. In this paper a methodology for hydraulic calculations of both forced and natural circulation loops is presented. The increased thermal safety margin of rifled tubes is predicted and compared with the safety margin of smooth tubes for uniform and variable heat loads among walls of the boiler furnace. The rifled tube provides an acceptable temperature of its wall even under a high void fraction of the coolant and prevents the occurrence of critical heat transfer conditions. The influence of the rifled tubes on an increase of the hydraulic resistance in the circulation loop is analyzed. Also, a range of operating conditions under which there is no need for the circulation pumps operation is determined.