省煤器的磨损及其防止

省煤器是锅炉的重要部件之一,主要作用为利用锅炉尾部烟气的热量加热给水并同时降低排烟温度,进入省煤器的烟气的温度已经很低,导致烟气中的飞灰的硬度大为增加,不可避免的会对管壁产生磨损,从而使省煤器管损坏。实践证明,省煤器的爆管事故多是由磨损导致的。加强省煤器的防磨具有十分重要的意义。     

某电厂后屏再热器爆管原因分析

分析了锅炉后屏再热器发生爆管的原因,管子受到高温烟气腐蚀,同时长时超温加剧腐蚀速率,使管壁减薄,减薄后的管子强度不足,从而引起爆管。     

生物质锅炉高温过热器腐蚀失效分析

针对某生物质锅炉高温过热器爆管进行失效分析,采用宏观检查、化学成分分析、金相检测、扫描电镜(SEM)和能谱(XPS)分析等方式对爆管管段损伤表面的微观组织形貌、腐蚀产物进行分析。分析表明:生物质燃料中碱金属氯化物和硫化物以灰分形式附着在管壁上,在高温条件下与管壁发生反应,生成低熔点共晶物,结构形式为易脱落的针状结构;折焰角处局部烟速较高,爆管附近受烟气气流的强烈冲刷,迎风侧管壁腐蚀产物脱落,新的腐蚀反应继续进行,管壁厚度不断减薄;磨损与腐蚀共同作用导致了爆管的发生。     

锅炉水冷壁爆管事故的分析

针对一起锅炉水冷壁爆管事故,从水冷壁的受热状态、水循环、管壁应力等方面进行了分析,指出局部水冷壁受热强,水循环流速缓慢,导致水冷壁金属超温过热;管内壁的汽水腐蚀、管外壁的高温氧化,再加上高速烟气气流对向火侧管壁金属的剧烈磨损,导致管壁金属发生严重减薄,承受的应力水平进一步提高;频繁的启、停锅炉以及压力波动、温度变化,导致水冷壁上部弯管部位金属既承受弯曲应力,又同时承受着较大的交变应力作用。由此得出造成局部水冷壁金属超温过热、高温腐蚀、磨损减薄以及交变压力等是导致爆管的主要原因。     

余热锅炉高温过热器爆管的控制

通过对一起炼焦余热锅炉过热器爆管事故的现场勘察,分析了引起爆管的原因,采用了设置管壁温度监测点的方法来控制和调整高温废气、管内介质的流量和温度,避免此类事故的再次发生。     

锅炉省煤器管件爆管原因与数值模拟分析

以某厂省煤器爆管事故为例,对省煤器失效管件断口进行宏观检查、材料化学成分分析、金相组织分析、微观形貌能谱分析和CFD数值模拟分析及最大磨损量的计算,最后提出采取必要的措施减少对管件的磨损,延长管件的使用期限。结果表明,锅炉炉内烟气飞灰颗粒长期对省煤器管束冲刷磨损使管壁不断减薄,最终导致爆管发生。建议对靠近烟气飞灰入口处的省煤器管加装防磨瓦,严格控制锅炉吹灰器的风速,烟气飞灰速度尽可能控制在9m/s,并采用错列布置方式减轻管束磨损。     

4.2 MW燃煤热风炉换热器壁温计算方法研究

推导了烟气在管内流动、均匀受热管壁的壁温计算公式,分析得出,影响壁温的主要因素是烟气温度和表面传热系数。降低管壁温度的有效方法是降低烟气温度,即在受热面前的高温烟气中混入冷烟气或冷空气,对降低壁温的两种方法进行了比较。研究了热风炉计算中过量空气系数、再循环系数的确定方法及热风炉对风温变化的适应性。     

某四角切向燃烧锅炉12Cr1MoV钢高温过热器爆管失效模式研究

针对某电厂四角切向燃烧锅炉12Cr1MoV高温过热器管近年来发生多次爆管事故,结合其锅炉结构、爆管现场检验结果与爆管失效分析结果,研究其过热器爆管失效模式及机理。研究发现：过热器爆管均为过热失效,爆口位置主要在管屏迎烟侧,其迎烟侧和背烟侧材料力学性能、组织球化和氧化皮厚度普遍存在明显的差异。研究表明：在炉内高温烟气作用下,过热器局部管屏迎烟侧管壁超温,由此引起其组织球化、材料力学性能劣化、蠕变裂纹的生成,多项因素的叠加导致最终爆管。     

关于余热炉中压蒸发器管屏爆管原因分析及对策

针对水泥余热炉中压蒸发器管屏爆管进行了分析研究,判断爆管产生的原因,并提出针对性改进措施,从而避免爆管的再次产生。     

水垢引起水冷壁爆管和锅筒鼓包爆破的原因及预防

1　前言锅炉是一种承压、受热 ,有爆炸危险的特种设备。在运行时会因为操作和管理不当而出现各种事故 ,其中由于水垢的生成而引起水冷壁爆管和锅筒鼓包爆破是低压锅炉较常见的一种事故。低压锅炉用水不纯净 ,其中含有许多杂质 ,如果这种水不经过水处理或水处理方法不当 ,直接注入锅炉内 ,再加上排污不及时 ,就会在锅筒内壁结生水垢。由于水冷壁和锅筒位于燃烧室直接受高温烟气的辐射和火焰冲刷 ,所以一旦水冷壁管和锅筒底部结生水垢 ,就很容易引起管壁 ,筒壁温度升高 ,过热变形 ,甚至发生爆管或鼓包破裂事故。2　水冷壁爆管和锅筒鼓包爆破的…     

平行流蒸发器内气液两相流分配均匀性实验研究

平行流蒸发器内气液两相(特别是液相)在各扁管间的分配对其传热性能影响较大,如果各扁管间的气液分配不均匀其传热性能将显著地下降.在不同气-液流量下实验研究了6种不同形式的平行流蒸发器的分支管液体流量分配情况,实验中观察到流型以环状流为主.研究发现,对于竖直向下流动和竖直向上流动,用通过增加管径的方法不能改善液体流量在各分支管的分配,而主管中气液入口的位置对于流量分配均匀性影响较大.     

Visualization and performance measurement of operating mesh-wicked heat pipes

This work presents visualization of the evaporation/boiling process and thermal measurements of operating horizontal transparent heat pipes. The heat pipes consisted of a two-layered copper mesh wick consisting of 100 and/or 200 mesh screens, a glass tube and water as the working fluid. Experimental results indicated that nucleate boiling was prompted for a wick having a fine 200-mesh bottom layer. When the fluid charge approximately equaled the pore volume in the wick, the water–vapor interface receded into more curved menisci with increasing heat load Q. Thus, larger capillary forces and evaporation areas were attained to meet the increasing need of liquid supply and evaporation rate at the water–vapor interface. At Q = 40 and 45 W, the water film became less than 100 μm and the nucleate boiling observed at lower heat loads disappeared. Optimal thermal characteristics with smallest thermal resistances across the evaporator and lowest overall temperature distributions were found for such a wick/charge combination. Under a smaller charge, partial dry-out was observed in the evaporator. Under a larger charge, liquid recession with increasing heat load was limited and bubbles grew and burst violently at high heat loads. The effects of different wicks and fluid charges on the evaporation/boiling characteristics were discussed.     

Experimental study on the operating characteristics of a flat bifacial evaporator loop heat pipe

There is growing demand for highly efficient heat transfer devices having excellent performance, operational stability and low power consumption. Although loop heat pipes satisfy these requirements, conventional loop heat pips have limited application to flat heat sources due to their mostly cylindrical evaporator shape. To overcome this limitation, various types of flat evaporator loop heat pipes have been developed, though their operational reliability is still uncertain. In this work, we focused on the development of a flat bifacial evaporator loop heat pipe, and its operating characteristics at transient and steady states are discussed in detail.     

Heat transfer characteristics of the evaporator section using small helical coiled pipes in a looped heat pipe

An experimental study was carried out for the heat transfer characteristics and the flow patterns of the evaporator section using small diameter coiled pipes in a looped heat pipe (LHP). Two coiled pipes: the glass pipe and the stainless steel pipes were used as evaporator section in the LHP, respectively. Flow and heat transfer characteristics in the coiled tubes of the evaporator section were investigated under the different filling ratios and heat fluxes. The experimental results show that the combined effect of the evaporation of the thin liquid film, the disturbance caused by pulsation and the secondary flow enhanced greatly the heat transfer and the critical heat flux of the evaporator section. In final, two dimensionless empirical correlations were proposed for predicting the heat transfer coefficients of the evaporator section before and after dryout occurs.     

Improvements of gravity assisted wickless heat pipes

The performance of conventional gravity assisted heat pipes and modified heat pipes with a separator in the adiabatic section is investigated experimentally. Heat pipes with a three layered wick in the evaporator section, in addition to the separator, are investigated. The performance of the modified heat pipes was compared to a reference gravity assisted heat pipe. Experiments were conducted on heat pipes of three lengths with a common diameter at constant evaporator and condenser lengths. The effect of varying the adiabatic length was, thus, investigated distinctly in normal heat pipes and in modified heat pipes with a separator. Water was employed as the working fluid in all heat pipes. The experimental program included five inclination angles and a heat flux range form 5 to 32 kW/m². The presence of the adiabatic separator caused a marked improvement in all heat pipes tested for all lengths and inclination angles. A pronounced reduction in heat pipe evaporator temperature was obtained, which is accompanied by an improvement in the heat transfer coefficient. A correlation was developed for prediction of the heat transfer coefficient for gravity assisted heat pipes with an adiabatic separator. The correlation took into consideration the effect of the varying adiabatic length. The correlation was in good agreement with the experimental data.     

An Experimental Study of Small-Diameter Wickless Heat Pipes Operating in the Temperature Range 200°C to 450°C

An experimental investigation is reported for medium-temperature, wickless, small-diameter heat pipes charged with environmentally sound and commercially available working fluids. The wickless heat pipes (thermosyphons) studied have many applications in heat recovery systems since their operational temperature range is between 200°C and 450°C. The heat pipes investigated had an internal diameter of 6 mm and a length of 209 mm. The lengths of evaporator and condenser sections were 50 mm and 100 mm, respectively. The working fluids tested were diphenyl based: Therminol VP1 and Dowtherm A. High-grade stainless steel was chosen as the shell material for the heat pipes to provide chemical compatibility between heat pipe casing material and working fluids at elevated temperatures. Thermal resistances of less than 0.4 K/W have been achieved at working temperatures of up to 420°C with an effective thermal conductivity of 20 kW/m-K, which corresponds to an axial heat flux of 2.5 MW/m². Even for such small-diameter heat pipes, the experimental data for the evaporator showed good agreement with Rohsenow's pool boiling correlation.     

System optimization and experimental research on air source heat pump water heater

This paper deals with the system optimization of air source heat pump water heater (ASHPWH), including calculating and testing. The ASHPWH system consists of a heat pump, a water tank and connecting pipes. Air energy is absorbed at the evaporator and pumped to storage tank via a Rankine cycle. The coil pipe/condenser releases condensing heat of the refrigerant to the water side. An ASHPWH using a rotary compressor heated the water from initial temperature to the set temperature (55 °C). The capillary tube length, the filling quantity of refrigerant, the condenser coil tube length and system matching are discussed accordingly. From the testing results, it could be seen that the system performance COP could be improved obviously.     

Study on a twin‐bed adsorption refrigeration system using R134a‐activated carbon pair

A low capacity twin‐bed adsorption refrigeration system has been built with R134a as a refrigerant and activated carbon as the adsorbent. Simple tube‐in‐tube heat exchangers have been fabricated and have been used as the adsorber beds. Activated carbon (granular type) has been filled in the annular space of the inner tube and outer tube. A plate heat exchanger has been used as the condenser and the temperature of cooling water has been maintained between 25°C and 30°C, also the evaporator has been custom designed as per requirements. A mathematical model has also been developed and the results obtained have been found to be comparable. While operating the system in the single‐bed mode a cooling power of 250.4 W has been obtained with a coefficient of performance (COP) of 0.38 with an average evaporator temperature of 18.4°C against a predicted value of 263.7 W with a COP of 0.41. While operating in the twin‐bed mode a cooling power of 281.3 W with a COP of 0.47 with an average evaporator temperature of 17.6°C has been obtained against a predicted value of 294.5 W with a COP of 0.52.     

Thermal performance characteristics of heat pipes

Theoretical and experimental studies are conducted to evaluate the overall thermal performance of single-component and gas-loaded heat pipes. In the analysis, the simple conduction model developed recently for the single-component heat pipes has been extended to predict the wall temperature profiles of gas-loaded heat pipes with phase change occurring in the evaporator wick. Experimental evaluation of the thermal performance is made with two working fluids (water and acetone) under two corresponding sink environments (boiling water and boiling alcohol). The heat pipe system is designed with variable-length heat input and output sections under a wide range of heat input conditions. Measured results agree well with theoretical predictions.     

The Study and Development of Roll Heat Pipe Performance

A new type of heat pipe called roll heat pipe (RHP) is considered in this study. In RHP, the evaporator and the condenser are separated in the radial direction, and the energy is moved in radial direction. RHP is composed of two concentric annular pipes of unequal diameter, wick structure, and bridge wicks, which provide the return path of the working fluid to evaporator. A heat source is inserted in the inner pipe, which works as the evaporator region. RHP can be applied as heat roll in the laser printers or copy machines where isothermal heating as well as rapid response is desired. Three RHP samples are fabricated and tested in this work. They differ in the number of bridge wicks and inner tube diameter. The length of all samples is 300 mm. In this paper, the transient thermal characteristics of RHP samples are investigated experimentally and compared with numerical analysis results. Also, the effects of fill charge on the performance of RHP samples are studied. By using infrared thermography camera, we observed that the level of temperature uniformity on the outer surface of heat roll is very good in comparison with real heat roll.