低温煤油结晶试验研究北大核心CSCD

针对煤油在低温下的结晶问题,设计了低温煤油结晶试验验证系统,运用低温氮气冷却和液氮冷却两种煤油冷却方式,模拟液氧煤油火箭发动机上的煤油降温流动过程及过冷煤油试验时煤油的降温情况。通过试验获取了两种冷却方式下的煤油温度、过滤器流量及过滤器前后压差。研究发现,低温氮气冷却后的煤油流经过滤器前后压差稳定,约为50—60 kPa,流阻与流量变化趋势基本吻合,未产生结晶;而液氮冷却后的煤油流经过滤器前后压差明显增大,最高可达250 kPa,且流阻存在突变现象,煤油中产生了结晶。     

氧气含量对超音速火焰喷涂燃烧特性的影响

超音速火焰喷涂过程中,火焰特征对涂层的形成产生重要的影响,应用β-PDF(Probability DensityFunction)湍流燃烧模型对喷枪燃烧室的燃烧过程进行了数值模拟,研究了混合状态与燃烧状态之间的关系.研究表明,随着氮气含量的增加,燃气温度下降,燃烧的最高温度点向低混合分数靠近,温度梯度增大,最高理论燃烧温度从3417K下降到2000 K;燃烧过程中存在大量中间产物,随着氮气的增加,燃烧过程中大量的单质碳析出,燃烧过程向低温燃烧转化.随着氮气含量和燃油的增加,燃烧产物中CO2的含量在最高温度点附近出现最高点,H2O次之,最后生成CO,C的含量呈现逐步递增的趋势.     

手动增压式液氮泵

介绍了获国家实用新型专利的手动增压式液氮泵。该泵用于与符合ＧＢ５４５８的液氮生物容器配套，向其它杜瓦、冷阱等输送液氮。评述了各种液氮传输方法，给出了新泵的原理、结构、使用方法。试验结果：平均流量达到４．１６Ｌ／ｍｉｎ，扬程大于２ｍ，传输效率９５％，质量１．６ｋｇ。使用结果证明新泵具有结构简单、质量轻、连接密封可靠、操作方便、省力、流量大、连续工作性能稳定、传输效率高等优点，是一种较为理想的液氮传输设备。     

冷氦直接增压排放推进剂试验系统的研制及性能调试

针对在液氧贮箱内贮存冷氦气并用于增压煤油贮箱排放的技术方案,研制了一套以液氮为冷源,借助换热器冷却常温氦气获得冷氦,继而送入煤油贮箱进行挤压排放的地面模拟试验系统。对该试验系统的主要功能进行了调试,包括流量调控测试,以及最大排液流量、制冷能力和贮箱内部温度分布测量等。结果表明,该试验系统能够安全可靠地模拟箭上冷氦增压系统的工作过程,可用于相关原理性验证试验和机理研究。     

分子筛在低温空分设备中的运用研究

比较了低温空分设备中H2O、CO2杂质的清除方法,在阐述分子筛吸附特性的基础上,重点论述了分子筛对H2O、CO2的吸附机理及吸附性能,并讨论了分子筛再生的方法选择和影响因素,得出了分子筛在低温空分设备中清除H2O、CO2可行性的结论.     

液氢温区冷氦增压系统试验研究

针对某型号火箭冷氦增压系统,建设了液氢温区冷氦增压系统试验平台,通过试验得到了冷氦气源压力和温度、冷氦加热器性能、模拟贮箱压力和温度的变化规律.结果表明:低温制冷机组配合高压低温换热贮罐可以真实模拟箭上的冷氦气源;根据对增压过程中贮箱压力的分析表明排气方式可以真实模拟箭上推进剂消耗过程中贮箱压力的变化情况;另外,试验中压力信号器、电磁阀和贮箱工作正常,验证了火箭冷氦增压系统的可靠性.     

浅谈禁油禁水工艺管道系统的压力试验

精细化工装置中禁油禁水工艺管道压力试验过程,根据系统压力及系统的大小不同,分别采用装置压缩空气对系统进行加压、装置压缩空气加高压气瓶的氮气加压、装置压缩空气加液氮增压汽化加压等不同方法,从而完成工艺管道的压力试验任务。本文详细介绍了该工艺过程。     

复合载荷作用下火箭输送管动力特性试验与数值研究

新型运载火箭多采用低温推进剂,增压输送系统作为火箭动力源头,其稳定性至关重要,因此新型增压输送管路的动力特性研究尤为关键。根据输送管路在箭上的实际安装状态,设计了大尺寸输送管路综合应力试验系统,此系统除传统的振动、控制系统之外,还包括低温液体加载系统、压力加载平衡系统、管路极限位移补偿系统、管路变形失稳防护系统。借助以上试验系统分析了管路结构在常温常压、充压、液氮充压状态下的管路结构的固有特性。依据试验分析结果建立并修正了管路有限元模型,结合试验对管路在箭上所经受的复合环境应力进行了仿真和试验研究,并对管路各部位动响应结果进行了分析。研究结果对不同类型的空间管路设计有着很强的指导意义。     

S-1型液氮输送器的设计

一、设计理由 在科研与生产中经常需要将低温液体如液氮从杜瓦瓶等低温容器中输入到低温设备 (如冷阱)中,此项工作在许多单位仍处在手工操作阶段,这样不但不经济,而且易产生危险。为了克服以上存在的问题,达到自动输送液氮的目的,我们设计TS—1型液氮输送器。 二、技术指标 1.液氮流量:0—100升/小时(可调); 2.气源压力:l—2公斤/厘米2; 3.表头压力:0.3—0.6公斤/厘米2。 三、工作原理 利用气源的气体压力作用在低温容器内液氮的液面上。在压差的作用下将液氮压入出液管,再由输液管送往冷阱或其他需用液氮的容器内。 四、结构 S—1型液氮…     

液氧贮箱增压过程中气枕空间温度场的数值模拟

液氧贮箱增压气体输送过程中,气枕空间的温度场会发生较大的变化,并且会引起相界面附近低温液体的温升.基于双膜阻理论建立热质交换模型,通过模拟贮箱内非稳态热流过程,分析气枕空间在增压气体输送过程中温度场的变化及其对于贮箱内低温液氧的影响.     

低温液体送入热管道后的升压过程

分析了低温液体输入热管道后升压过程，并对输送过程中的临界质量流进行了计算，结合有关文献的实验数据，给出输送过程中的压力计算公式。并提出了减少压力最大值的方法，对于低温液体输送参数的确定，管道的设计提供参考。     

筛网LAD通道液氮动态出流性能研究

为了研究筛网LAD通道结构在低温推进剂中的气液分离及输送性能,设计、加工了覆盖筛网的圆管通道并通过可视化实验获得了液氮中LAD通道有效工作时的极限排放高度,并分析了流动损失的组成.结果 表明,325×2300 Dutch Twill型编织筛网在自增压过程中发生泡破时的液氮极限排放高度为280 mm,所产生的水力静压损失...     

低温液体火箭发动机循环预冷模拟试验

进行了低温液体火箭发动机自然循环预冷过程的模拟实验,试验证明了回流管进入储箱液面之上和进入液面之下的两种方案均可实现自然循环预冷,但是要维持自然循环继续进行,前者必须增加引射,而后者不需引射。模拟试验结果可供进一步试验研究参考。     

Basic study on new cryogenic refrigeration using CO2 solid–gas two phase flow

In this paper, a cryogenic refrigeration method is described, which utilizes CO₂ solid–gas two phase flow and the dry ice. The CO₂ solid–gas two phase flow is achieved by expanding liquid CO₂ and thus refrigeration process less than CO₂ triple point −56.6 °C can be available. The experimental work is divided into two parts and two experimental set-ups were designed, constructed and tested. The interest of the first experiment test is the feasibility of expanding liquid CO₂ into CO₂ solid–gas flow in a horizontal circular tube by expansion valve. The second experiment focuses on the feasibility of the refrigeration of liquid CO₂ expanding into solid–gas two phase flows used in a prototype CO₂ heat pump system. The results show that solid–gas two phase flows can be achieved by expanding liquid CO₂ by expansion valve in a closed CO₂ heat pump system loop and low temperature refrigeration below −56.6 °C is achieved in the experiments, which give greater possibility to create a cryogenic refrigeration process below −56.6 °C for food industries, bio-medical engineering, etc.     

Numerical simulation of cryogenic cavitating flow by an extended transport-based cavitation model with thermal effects

Thermodynamic effects on cryogenic cavitating flow is important to the accuracy of numerical simulations mainly because cryogenic fluids are thermo-sensitive, and the vapour saturation pressure is strongly dependent on the local temperature. The present study analyses the thermal cavitating flows in liquid nitrogen around a 2D hydrofoil. Thermal effects were considered using the RNG k-ε turbulence model with a modified turbulent eddy viscosity and the mass transfer homogenous cavitation model coupled with energy equation. In the cavitation model process, the saturated vapour pressure is modified based on the Clausius-Clapron equation. The convection heat transfer approach is also considered to extend the Zwart-Gerber-Belamri model. The predicted pressure and temperature inside the cavity under cryogenic conditions show that the modified Zwart-Gerber-Belamri model is in agreement with the experimental data of Hord et al. in NASA, especially in the thermal field. The thermal effect significantly affects the cavitation dynamics during phase-change process, which could delay or suppress the occurrence and development of cavitation behaviour. Based on the modified Zwart-Gerber-Belamri model proposed in this paper, better prediction of the cryogenic cavitation is attainable.     

基于AMESim的液氮可控传输性能分析

针对超低温冷却加工液氮可控传输难题,分析了热流量、管路压降等复杂因素对液氮可控传输的影响机制,提出了基于AMESim的液氮可控传输性能分析方法,建立了受热管道液氮两相流动传热数值模型,并在此基础上,研制出一套液氮可控传输原理性系统。通过对比实验表明,提高系统的输入压力能够增大低温流体的流量,缩短系统进入热平衡状态的时间,提高输出流体的干度和流型的稳定性;研制出的液氮可控传输原理性系统在输入压力为1.3 MPa时,在一定的开口范围内,能够稳定输出流量可控的低干度流体,且符合超低温冷却加工的要求。     

Capacitance-based liquid holdup measurement of cryogenic two-phase flow in a nearly-horizontal tube

Liquid holdup measurement of cryogenic fluids is an area of considerable significance because of its inevitable occurrence in LNG transportation, rocket propellant delivery and superconducting equipment cooling, etc. To measure the liquid holdup of cryogenic two-phase flow, a capacitance sensor was carefully designed, which consists of a pair of optimized concave-electrode form with the electric circuit for the small capacitance detection. Four flow patterns were realized to evaluate the performance of the sensor in visualization experiments with liquid nitrogen and vaporous nitrogen. An image method was employed to calibrate the capacitance sensor, which led to a mathematical relationship between the capacitance and the liquid holdup. The results indicated that the obtained correlation between liquid holdup and capacitance satisfactorily coincided with the measured data.     

Free-surface flow of liquid oxygen under non-uniform magnetic field

The paramagnetic property of oxygen makes it possible to control the two-phase flow at cryogenic temperatures by non-uniform magnetic fields. The free-surface flow of vapor-liquid oxygen in a rectangular channel was numerically studied using the two-dimensional phase field method. The effects of magnetic flux density and inlet velocity on the interface deformation, flow pattern and pressure drop were systematically revealed. The liquid level near the high-magnetic channel center was lifted upward by the inhomogeneous magnetic field. The interface height difference increased almost linearly with the magnetic force. For all inlet velocities, pressure drop under 0.25 T was reduced by 7–9% due to the expanded local cross-sectional area, compared to that without magnetic field. This work demonstrates the effectiveness of employing non-uniform magnetic field to control the free-surface flow of liquid oxygen. This non-contact method may be used for promoting the interface renewal, reducing the flow resistance, and improving the flow uniformity in the cryogenic distillation column, which may provide a potential for enhancing the operating efficiency of cryogenic air separation.     

Liquid nitrogen injection into water: Pressure build-up and heat transfer

This paper is concerned about the expansion of a small amount of liquid nitrogen injected into a relatively large pool of water and the heat transfer behaviour during the process. Both the transient pressure and temperature profiles are experimentally measured and analysed. The results show that the pressure and the rate of pressure rise increase approximately linearly with increasing injection pressure and reach, respectively, to 284 kPa and 500 kPa/s at a liquid nitrogen injection velocity of ∼0.85 m/s. The temperature varies little during the injection process due to relatively small amount of liquid nitrogen injected. A comparison of the experimental results with related work on surface boiling of cryogen suggests that the heat transfer of direct mixing be much stronger than boiling on smooth surfaces and flow boiling through smooth pipes, but comparable to the boiling on very rough surfaces and flow boiling in pipes with porous inserts. A comparison with the results generated by injecting a small amount of water into liquid cryogens shows that a higher pressure increase rate could be achieved if operating conditions are optimised to induce fragmentation. Implications of the results to cryogenic engine work output and ways to improve the performance of cryogenic engines are also discussed.     

低温罩表面结霜过程数值模拟

对低温罩表面结霜过程进行了数值模拟研究。通过能量和质量平衡方程建立了低温罩结霜的物理模型,考虑了霜层厚度增加的传质和传热过程。据此分析了来流空气的温度、相对湿度、速度及冷壁面温度对霜层表面温度和霜层厚度的影响。计算结果表明,来流空气的温度及冷壁面温度对结霜的影响较大,而来流空气的速度和相对湿度对结霜的影响则较小。最后指出了对低温罩在加注低温液体时采取隔热防霜措施的必要性。