液氧液甲烷同温共底贮存瞬态热力特性仿真研究

针对大面积冷屏保护下的液氧/液甲烷同温共底贮箱,建立了耦合真空多层绝热与主动制冷系统的瞬态传热模型,研究了液氧/液甲烷共底自增压与零蒸发贮存过程中贮箱外部绝热结构与内部气液相的热力参数变化规律,讨论了共底夹层采用不具有绝热能力的材料对液氧/液甲烷共底零蒸发贮存特性的影响。研究结果表明,在适当的冷量输入条件下,大面积冷屏方案可以实现外界漏热的有效阻挡;采用铝合金共底夹层有利于稳定液氧和液甲烷的共底贮存状态,使液氧/液甲烷在20 h内快速达到热平衡;在零蒸发贮存周期内,液氧/液甲烷共底贮存温度波动小于0.2 K,压力波动小于2.46 kPa且具有抗热扰动的能力。     

低温推进剂贮箱绝热性能实验研究

针对低温推进剂长时间在轨贮存的要求,搭建了绝热系统地面验证测试装置。本测试装置通过维持高真空及恒壁面温度条件,可以较好地模拟在轨条件;通过贮箱颈管处设置的温度补偿器,有效的屏蔽掉颈管导热漏热。测试装置可实时监测系统中的真空度及壁面温度变化,可对贮箱蒸发排出气体流量和绝热系统不同位置的温度分布进行测量。针对10 mm硬质聚氨酯泡沫和30层多层绝热的复合绝热系统,在真空度2×10-3Pa,冷热壁面温度分别为96 K和313 K条件下,测得液氮日蒸发率为0.210%,折算液氧日蒸发率为0.156%。     

低温推进剂长时间在轨的蒸发量控制关键技术分析

介绍了国外低温推进剂应用需求,从被动防护和主动制冷等方面对低温推进剂长时间在轨蒸发量控制关键技术进行了归纳分析,对国外低温推进剂长时间在轨蒸发量控制系统技术方案进行了研究,对低温推进剂蒸发量控制技术进行了总结和展望.     

低温推进剂无损贮存技术试验研究进展

液氢/液氧等低温推进剂,由于其高性能优势被作为深空探索使用推进剂,但低温推进剂长时间在轨应用,主要受限于低沸点的推进剂受热蒸发所带来的贮箱压力控制和蒸发损失等一系列问题,需要发展低温推进剂无损贮存技术来解决。文章介绍了应用低温制冷机结合换热技术实现贮箱内低温推进剂无损贮存的试验情况,总结其发展趋势和展望。     

低温推进剂在轨压力控制方法及效能对比分析

针对液氢、液氧低温推进剂在轨贮存时长及排气量,建立了直接排气和热力排气数学模型。在0.13—0.14 MPa和0.2—0.3 MPa两种控压区间分析了40 W和100 W漏热环境下的贮箱排气量的对比分析,结果表明液氧易于实现长期无损贮存,而液氢在轨无损贮存时间相对较短,若要实现10天或更长时间的空间任务,有必要对液氢贮箱采用热力学排气技术进行压力控制,降低液氢蒸发量。对基于热力学排气技术的液氢在不同工况下的排气量进行了计算,根据液氢在轨任务时长的要求给出了合适的控压方式选择方向。     

低温推进剂贮箱气冷屏复合绝热结构综合优化设计

气冷屏复合绝热(VSC)结构可以有效减少低温推进剂蒸发损耗。目前尚缺乏对气冷屏复合绝热结构的综合优化设计,现有的研究方法不能准确反映出漏热量与多层变密度材料导热性能及冷屏屏位之间的关系。为此,考虑多层变密度材料导热系数随冷屏位置的变化,对复合绝热结构进行综合优化设计,研究冷屏位置和多层变密度结构的相互影响规律,分析了最佳层密度与最佳屏位。结果表明,加入气冷屏后,降低中密度区层密度,增加高密度区层密度可以进一步减少漏热量。对于不同的层密度组合,存在一个最佳屏温,当冷屏处于该温度时漏热量最小。     

基于二氧化硅气凝胶制备的多层隔热材料微观结构及热性能研究

成功制备了一种新型多层隔热材料, 其间隔层基于氧化铝纤维制备, 并由溶胶-凝胶法植入二氧化硅气凝胶颗粒。在高真空环境下(10^-3 Pa), 新型多层隔热材料当量热导率比传统材料低21.8%, 同时重量比传统材料降低了67.2%。此外, 这种新型多层隔热材料在1200 K的高温以及低真空条件下(100 Pa)也表现出良好的隔热性能。     

卧式高真空多层绝热低温容器无损贮存规律

介绍了卧式低温容器的传热特点,以及低温液体无损贮存的传热模型.通过2m3卧式高真空多层绝热低温容器在90%、85%和80%初始充满率下的静态无损贮存试验,拟合现有的传热模型,对升压过程中不同规律的3个阶段进行了分析,得到了第一、第三阶段升压的初步规律.     

充注率及压力控制带对热力排气系统性能的影响

热力排气系统是通过流体混合与节流换热排气双重作用实现低温推进剂在轨长期贮存的一种有效的压力控制技术。本研究搭建了以R141b为气液相变存储介质的室温温区热力排气系统模拟装置,进行了介质充注率分别为35%、50%、65%和压力控制带分别为(80~85)kPa、(80~90)kPa、(80~95)kPa的贮箱压力控制实验研究,获得了充注率及压力带对热力排气系统作用下贮箱增压特性和排气损失的影响规律。研究结果表明,充注率越大,排气损失越大;随着压力控制带宽度的增加,排气损失先减小后增大。上述结果对今后液氮、液氧等低温工质的热力排气研究具有指导作用。     

在轨低温推进剂储存地面试验研究

拟采用薄膜电加热片模拟太阳照射空间热环境、采用以液氮液氢为低温介质的冷屏模拟深空低温环境,以热缩比模型代替全尺寸的试验研究。该技术可同时实现对高温热流、低温热流及瞬态热流变化的模拟,为低温推进剂蒸发量抑制地面验证试验提供不同高度的空间热试验环境。另外文章还对数据测量在真空热试验中的应用情况作了简要介绍。     

Wrapped multilayer insulation design and testing

New vehicles need improved cryogenic propellant storage and transfer capabilities for long duration missions. Multilayer insulation (MLI) for cryogenic propellant feedlines is much less effective than MLI tank insulation, with heat leak into spiral wrapped MLI on pipes 3–10 times higher than conventional tank MLI. Better insulation for cryogenic feed lines is an important enabling technology that could help NASA reach cryogenic propellant storage and transfer requirements. Improved insulation for Ground Support Equipment could reduce cryogen losses during launch vehicle loading. Wrapped-MLI (WMLI) is a high performance multilayer insulation using innovative discrete spacer technology specifically designed for cryogenic transfer lines and Vacuum Jacketed Pipe (VJP) to reduce heat flux.The poor performance of traditional MLI wrapped on feed lines is due in part to compression of the MLI layers, with increased interlayer contact and heat conduction. WMLI uses discrete spacers that maintain precise layer spacing, with a unique design to reduce heat leak. A Triple Orthogonal Disk spacer was engineered to minimize contact area/length ratio and reduce solid heat conduction for use in concentric MLI configurations.A new insulation, WMLI, was developed and tested. Novel polymer spacers were designed, analyzed and fabricated; different installation techniques were examined; and rapid prototype nested shell components to speed installation on real world piping were designed and tested. Prototypes were installed on tubing set test fixtures and heat flux measured via calorimetry. WMLI offered superior performance to traditional MLI installed on cryogenic pipe, with 2.2 W/m² heat flux compared to 26.6 W/m² for traditional spiral wrapped MLI (5 layers, 77–295 K). WMLI as inner insulation in VJP can offer heat leaks as low as 0.09 W/m, compared to industry standard products with 0.31 W/m. WMLI could enable improved spacecraft cryogenic feedlines and industrial hot/cold transfer lines.     

Design,fabrication and test of Load Bearing multilayer insulation to support a broad area cooled shield

Improvements in cryogenic propellant storage are needed to achieve reduced or Zero Boil Off of cryopropellants, critical for long duration missions. Techniques for reducing heat leak into cryotanks include using passive multi-layer insulation (MLI) and vapor cooled or actively cooled thermal shields. Large scale shields cannot be supported by tank structural supports without heat leak through the supports. Traditional MLI also cannot support shield structural loads, and separate shield support mechanisms add significant heat leak. Quest Thermal Group and Ball Aerospace, with NASA SBIR support, have developed a novel Load Bearing multi-layer insulation (LBMLI) capable of self-supporting thermal shields and providing high thermal performance.We report on the development of LBMLI, including design, modeling and analysis, structural testing via vibe and acoustic loading, calorimeter thermal testing, and Reduced Boil-Off (RBO) testing on NASA large scale cryotanks.LBMLI uses the strength of discrete polymer spacers to control interlayer spacing and support the external load of an actively cooled shield and external MLI. Structural testing at NASA Marshall was performed to beyond maximum launch profiles without failure. LBMLI coupons were thermally tested on calorimeters, with superior performance to traditional MLI on a per layer basis. Thermal and structural tests were performed with LBMLI supporting an actively cooled shield, and comparisons are made to the performance of traditional MLI and thermal shield supports. LBMLI provided a 51% reduction in heat leak per layer over a previously tested traditional MLI with tank standoffs, a 38% reduction in mass, and was advanced to TRL5. Active thermal control using LBMLI and a broad area cooled shield offers significant advantages in total system heat flux, mass and structural robustness for future Reduced Boil-Off and Zero Boil-Off cryogenic missions with durations over a few weeks.     

Study on effect of liquid level on the heat leak into vertical cryogenic vessels

The diminishing of heat leak into cryogenic vessels can prolong the storage time of cryogenic liquid. With the storage of cryogenic liquid reducing, the heat leak decreases, while the actual storage time increases. Compared with the theoretical analysis, the numerical simulation can more accurately calculate the heat transfer and temperature distribution in the vessel with complex structure. In this paper the steady state heat leak into cryogenic vessels with different liquid level height is analyzed using a finite element model. And liquid nitrogen boil-off method was adopted in experiments to validate the result of numerical simulation. Experimental results indicate favorable agreement with numerical simulation by ANSYS software. The effect of liquid level on heat leak into the cryogenic vessel can be considered in calculation of storage time and structure design.     

Heat flux from 277 to 77 K through a few layers of multilayer insulation

The insulating ability of a multilayer insulation (MLI) system, consisting of a few layers on an aluminium taped 77 K surface, was experimentally studied to understand quantitatively how thermal performance changes with the number of multilayers and vacuum level. This information can help to make design decisions trading-off the cost of material and installation manpower against liquid nitrogen consumption in many cryogenic applications. The ratios of the measured heat flux for different systems are: Q(_painted) : Q(_taped) : Q(_{5 layers}) : Q(_{10 layers}) : Q(_{20 layers}) Q(_{30 layers}) = 1 : 0.19 : 0.06 : 0.037 : 0.027 : 0.022. The effective thermal conductivity also increases with the number of layers so only a marginal benefit can be gained in excess of 30 layers; for large liquid vessels 30–40 layers are recommended. The heat flux and temperature distribution in the MLI were also measured as functions of vacuum pressure. The temperature of the last layer is closer to the temperature of the warm box than that of the first layer is to the cold surface, even if the last layer is separated from the warm box and the first layer is in contact with the cold surface. The results and heat transfer mechanisms through MLI are analysed and discussed.     

低温阀热锚位置优化及漏热分析

气动低温调节阀是大型氦低温系统中最重要的执行机构,工作在极低温状态下(液氢/液氦温区:20—4 K),低温漏热量是其最重要的技术参数之一。通过在低温阀外管焊接77 K热锚,可以有效降外管的漏热量损失。通过引入热力完善度,优化热锚在外管的相对位置,结果显示:热锚安装的最佳相对位置为0.40,此时外管在4 K温区相对漏热量损失减少了82.5%。     

Final test results for the ground operations demonstration unit for liquid hydrogen

Described herein is a comprehensive project—a large-scale test of an integrated refrigeration and storage system called the Ground Operations and Demonstration Unit for Liquid Hydrogen (GODU LH2), sponsored by the Advanced Exploration Systems Program and constructed at Kennedy Space Center. A commercial cryogenic refrigerator interfaced with a 125,000 l liquid hydrogen tank and auxiliary systems in a manner that enabled control of the propellant state by extracting heat via a closed loop Brayton cycle refrigerator coupled to a novel internal heat exchanger. Three primary objectives were demonstrating zero-loss storage and transfer, gaseous liquefaction, and propellant densification. Testing was performed at three different liquid hydrogen fill-levels. Data were collected on tank pressure, internal tank temperature profiles, mass flow in and out of the system, and refrigeration system performance. All test objectives were successfully achieved during approximately two years of testing. A summary of the final results is presented in this paper.     

Passive ZBO storage of liquid hydrogen and liquid oxygen applied to space science mission concepts

Liquid hydrogen and oxygen cryogenic propulsion and storage were recently considered for application to Titan Explorer and Comet Nuclear Sample Return space science mission investigations. These missions would require up to 11 years of cryogenic storage. We modeled and designed cryogenic propellant storage concepts for these missions. By isolating the propellant tank’s view to deep space, we were able to achieve zero boil-off for both liquid hydrogen and oxygen propellant storage without cryocoolers. Several shades were incorporated to protect the tanks from the sun and spacecraft bus, and to protect the hydrogen tank from the warmer oxygen tank. This had a dramatic effect on the surface temperatures of the propellant tank insulation. These passive storage concepts for deep space missions substantially improved this application of cryogenic propulsion. It is projected that for missions requiring larger propellant tank sizes, the results would be even more dramatic.     

LNG低温输送管路的绝热保冷

从绝热性能、外形尺寸与重量、施工工艺、制造成本及维护、使用寿命五个方面对PUH、PUB改性聚氨酯泡沫塑料包覆绝热与真空多层绝热的低温液体管道输送进行了比较,分析了各自在使用上的优势与不足。     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.