Failure analysis of the brass tubes in a lubricating oil cooler

Failure analysis was carried out on leaked brass tubes of a lubricating oil cooler. Direct evidences of dezincification and stress corrosion cracking (SCC) were observed by scanning electron microscope (SEM) and energy dispersive spectroscopic (EDS) analysis. It is found that there are many small pits distributed on the fracture surface and EDS analysis revealed the occurrence of dezincification in the small pits. SCC was observed on the cross-sectional plane of the fracture by SEM. Ammonia test has proved the existence of residual stress in the as-received tubes. It is determined that the brass tubes have been suffered from the co-action between dezincification and SCC.     

辐冷器在复合制冷系统的优化设计

针对某一选定的复合制冷系统辐冷器结构方案,通过对辐冷器制冷降温机理的进一步深入分析,采用非比例热原理和数值计算相结合的方法对其结构尺寸进行优化设计.通过优化,该辐冷器在满足复合制冷系统制冷要求的前提下,外形结构尺寸大幅度减小,实现了优化设计的目的.     

模态分析在辐射制冷器设计中的应用

辐射制冷器主要为红外探测器提供合适的低温工作条件,是星载红外遥感探测系统的重要组成部分,其可靠性的高低和制冷性能的好坏将直接影响红外成像质量和遥感卫星的成败.建立了W型辐射制冷器结构的有限元模型,应用MSC/Nastran软件完成了模态、静力、正弦振动响应计算,进行了结构强度和振动模态分析,预示和验证了辐射制冷器的结构性能,为其结构设计改进提供了可靠理论依据.     

Degradation of mechanical strength of pyrolysis furnace tubes by high-temperature carburization in a petrochemical plant

Pyrolysis furnace tubes made of HP45 heat-resistant steel casting to handle carbonaceous gases at about 850 °C in a petrochemical plant developed longitudinal cracks after less than one-third of the expected life. Detailed microstructural analysis showed that the cracks were developed by a ductile intergranular mode. This was correlated with high-temperature carburization attack leading to massive precipitation of intergranular carbides and a mixture of carbides and sigma phase within the matrix. Experimental results suggested that the highly reducing nature of the environment precluded the tube material from developing and maintaining a surface protective oxide scale, which facilitated the rapid inward diffusion of carbon.     

氧压机水冷却器换热效果不佳的处理

60000m3/h空分设备配套氧压机多次出现因三级出口氧气温度过高报警而停车的现象,由于氧压机低压缸内所有的中间冷却器均整合在壳体内,不易拆卸清洗,于是在冷却水管上加装1个DN100mm的球阀,对各级冷却器进行反向冲洗。反向冲洗后效果明显,降低了氧压机的排气温度,保证其安全运行。     

1500m~3/h空分设备主冷泄漏分析及处理

1500 m3/h空分设备在运行过程中,因为主冷板式单元的部分氧通道泄漏,产品氧气纯度下降,更换整个主冷板式单元后故障消除。介绍故障现象和原因分析过程,阐述主冷板式单元更换方案和实施效果。     

40000m~3/h空分设备空气增压机级间冷却器效率低分析

福建炼化林德气体有限责任公司2套40000 m3/h空分设备配套的空气增压机在调试过程中,级间冷却器的冷却效果不理想,冷却后的空气温度偏高。对冷却器经多次检修,仍无法达到预期效果,最后被迫更换换热管束。介绍了故障发生时级间冷却器的运行参数和故障现象,阐述故障排查和处理过程,并对该类型翅片管换热器的选型、安装和维护提出建议。     

一种新型地球同步轨道卫星辐射制冷器的研制

提出了一种新型拼接式太阳屏的三级辐射制冷器概念,可有效提高制冷器的制冷效率.完成了样机研制,地面热模拟试验制冷性能:夏至有阳光时100 K/67 mW,无阳光时85 K/47.4 mW和90 K/86.4 mW,可以满足多元探测需求.     

脉冲管制冷机中板弹簧的有限元分析

利用ANSYS有限元分析软件对外径为120 mm的板弹簧进行了应力和轴向刚度分析,得出了弹簧的厚度、涡旋角、涡旋槽个数以及涡旋槽宽度这些几何参数与其应力分布特性和轴向刚度性能的关系.首次提出了一个刚度应力比的概念,用刚度应力比值的大小来评价板弹簧性能的好坏,并将其作为板弹簧的设计依据.     

主冷碳氢化合物含量超标的分析及处理

介绍一起52000 m3/h空分设备主冷碳氢化合物超标故障。根据空分系统各个单元可能造成主冷碳氢化合物含量超标的原因进行了排查分析,得出碳氢化合物超标原因是空压机组空气吸入口位置不合适,造成煤化工装置排放的碳氢化合物被吸入空压机,进而进入空分设备。提出了安全措施。     

Comparison of two different ways of using inertance tube in a pulse tube cooler

It is well known that the pressure wave should lead the volume flow rate at the ambient end of the pulse tube for a high-efficiency operation of a pulse tube cooler. Inertance tube can provide such a phase relationship without DC flow problem. However, inertance tube is always connected with a reservoir in previous literatures. Through theoretical calculation here, inertance tube without a reservoir can also provide a rather large phase-leading effect. Thus phasor diagram is used to analyze the relationship between phase-leading requirement and the pulse tube geometry. Roughly speaking, a larger void volume of pulse tube would require a larger phase-leading effect. Comparison experiments are also done on a thermoacoustically-driven pulse tube cooler. With i.d.2 mm tube as inertance tube, the tube without reservoir yields close results in terms of lowest temperature to that of the tube with reservoir and both give much better performance than that of an orifice with reservoir. Finally, the advantages of using inertance tube without reservoir are given.     

Impact of classical assumptions in modelling a microchannel gas cooler

Most of the current air-to-refrigerant heat exchanger models use the classic ?-NTU approach, or some of its assumptions. These models do not account for longitudinal heat conduction in the tube and the fin, and the heat conduction between different tubes. This paper presents a more fundamental numerical approach to heat exchanger modelling which takes into account the 2D longitudinal heat conduction in any element, does not apply the fin theory, and captures a more detailed representation of air properties. Using the fundamental numerical approach, the paper assesses the impact of the traditional heat exchanger model assumptions when modelling a microchannel gas cooler working with CO₂. The study revealed significant differences in capacity predictions depending on the ?-NTU relationship adopted. Large errors in capacity prediction of individual tubes occurred due to the adiabatic-fin-tip assumption when the neighbouring tubes were of different temperature.     

一种高频热驱动脉冲管制冷机不稳定现象的研究

报道了一种高频驻波热声发动机驱动脉冲管制冷机的热声不稳定现象.通过实验对此种热声不稳定现象的产生原因进行了探讨,发现增加加热功率或缩短声压放大器可以抑制此种不稳定现象;理论方面主要通过快速傅立叶变换对不稳定的压力波形进行分析,对其产生原因进行了初步分析.     

混合物和纯氮工质在一种JT节流制冷机上热力性能的对比实验

报道了采用混合物工质及纯氮工质在一种开式快速ＪＴ节流制冷机上的实验对比研究。采用纯氮工质在压力为１１．０Ｍｐａ左右，该ＪＴ节流冷机可获得的最低温度为８３－８４Ｋ，启动时间是７５Ｓ左右；而采用混合物质后，在压力为５．０ＭＰａ左右，该制冷机可获得７３－７４Ｋ的最低温度；降温时间与纯氮相当。     

跨临界二氧化碳热泵热水系统气冷器的仿真分析

建立了跨临界二氧化碳热泵热水系统中的气体冷却器模型，对管内二氧化碳和水侧的流动和传热进行了数值仿真；并运用该模型分析了系统运行时各有关参数对换热器性能的影响，并结合最优排气压力，研究使系统高效运行的方法，为气冷器的优化设计提供了基础。     

90000m~3/h空分设备直接空冷器排汽管道整体应力分析方案探讨

利用CAESARⅡ应力分析软件对90000 m3/h空分设备的直接空冷器排汽管道进行了整体应力分析。根据相关标准要求及工程实践经验,考虑了管道在内压、自重、热胀、基础差异沉降、地震和风荷载等荷载作用下管道的受力情况,并通过荷载工况的组合作用,得出各个工况下管道的应力分布和各个支吊点、设备接口的受力情况,并进行了补偿器的初步选型,为90000 m3/h空分设备直接空冷器排汽管道设计提供了解决方案。     

W型辐冷器环模试验与在轨测试比较

对某型号卫星搭载的W型辐冷器的热地面热环境模拟试验情况作了详细介绍,重点对其可能产生的误差进行了深入的分析.通过对比热环境模拟试验测试数据以及在轨遥测数据,分析得出两者之间的相对误差在1%左右,证明验证辐冷器性能的热环境模拟试验方案是合理的、准确的.     

自由活塞式斯特林制冷机压缩活塞间隙密封泄漏的数值模拟

采用数值模拟的方法,基于压力波和活塞位移波的简谐变化规律,对自由活塞式斯特林制冷机压缩活塞与气缸的间隙密封内氦气建立数值模型,模拟了间隙内氦气在不同工况下的层流流动。结果显示在一个周期内,流过间隙密封的气体体积净流量为0,质量净流量不为0,净流量方向从压缩腔流向背压腔,会造成活塞在工作中向压缩腔偏移。分析结果显示压力波和间隙宽度对泄漏量的影响较大,随充气压力、压比以及间隙的增大,泄漏量增加;活塞运动对其影响较小,当活塞位移波与压力波的相位差小于90°时,相位差增大,泄漏量增加,活塞频率增大,泄漏量增加。     

Stability of localized bulging in inflated membrane tubes under volume control

We study the stability of localized bulging solutions in an inflated hyperelastic membrane tube using an energy stability criterion. We first use this criterion to confirm a previously known result obtained using a dynamic stability criterion, namely that under pressure control all such bulging solutions are unstable. It is then shown that, under volume control, the solutions in the early stages of bulging are unstable whereas those in the later stages of bulging are stable. To be more precise, it is found that the unstable solutions correspond exactly to the snap-back section of the associated pressure-volume diagram.     

Origins of tensile stress-induced circumferential cracking of waterwall tubes in boilers

Abstract

The leakage and rupture of boiler tubes in power plants is a serious problem that can lead to unscheduled and costly outages. The predominant failure location of current concern is circumferential cracking on the fireside of waterwall tubes in the furnace waterwall section of a boiler. Although there is basic agreement that cracking results from a combination of thermal fatigue and corrosion, a complete explanation of the basic phenomena needed to establish the root causes of this problem is lacking. The purpose of the present study was to analyse the sources of the tensile stress responsible for initiating circumferential cracking and to identify the key parameters controlling this tensile stress. The results of analytical modelling suggested that a combination of increasing tube wall temperature with increasing thickness of internal oxide layers, and temperature spiking due to deslagging events eventually may result in tensile stresses sufficient to crack the fireside oxide and initiate the development of circumferential cracks. This scenario also led to suggestions for reducing tensile stresses in waterwall tubes which, in turn, would be expected to delay/avoid circumferential cracking and improve the reliability of waterwall tubes.