低温推进剂火箭发动机循环预冷系统喷泉非稳现象的数值研究

通过数值模拟,分析了低温推进剂(液氧)火箭发动机循环预冷系统中喷泉非稳现象的过程与机理;计算分析了不同影响因素下的喷泉现象及行为规律;同时,参照针对竖直立管的喷泉失稳边界Murphy曲线,对比探讨了输送管几何与保温参数影响下的自然循环预冷回路的喷泉稳定性边界;进一步地,针对特定循环预冷回路,数值分析并验证了消除喷泉效应的有效措施.     

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。     

氦气/液氧喷射泵水调试验

在水调试验台上对自行设计的氦气/液氧喷射泵进行了试验研究.研究结果表明,在其它条件相同的情况下,随着氦气耗量增加,液氧流量呈先增加后减小趋势,其最大值对应的氦气压力比为1.62-2.95,引射效率约100-160.实践表明,水调试验结果与预冷循环系统调试结果基本一致,为预冷循环系统喷射泵设计提供了高可靠的模拟环境.     

90K低温下带预冷的林德制冷机的系统设计

为了获得90K的低温,提出1套带预冷循环的林德制冷系统,并分别对该系统的预冷循环和制冷循环进行了设计.预冷系统和制冷循环的制冷剂分别为R404A 和 R740.无热负荷时,设定低温箱的温度90 K,制冷量为140 W.该系统整体结构简单,获取温度低,在低温领域有较广泛的应用.     

引射吸收式制冷循环

提出了引射吸收式制冷循环。它可以强化吸收,而且可以扩大吸收式制冷的应用领域。分析了引射吸收式制冷循环,提出了参数选择方法,分析了影响引射式吸收制冷循环中吸收过程的因素并与喷淋吸收过程进行了比较。     

基于氮制冷循环预冷的氢液化流程研究北大核心CSCD

为寻求简单可靠的预冷方法作为氢液化高能耗替代,提出一种基于氮气逆布雷顿循环预冷的氢液化流程,相比于混合工质预冷循环,该流程结构简单,成本较低,适用于中小型氢液化系统。利用MATLAB软件建立了该流程的热力学模型,并利用Globalsearch求解器进行了优化分析;经对各种预冷方式的计算比较,氮气循环的能耗(2.68 kWh/kg)介于混合工质及液氮预冷之间,但其总热流比混合工质预冷更少。通过进行优化计算,该流程在传统液化系统的基础上能耗显著降低,能够达到8.33 kWh/kg。     

某型氢氧火箭发动机射前预冷改进方案试验研究

为了简化射前操作流程,提高火箭发射可靠性,开展了针对某燃气发生器循环氢氧火箭发动机的射前预冷方案改进研究。研究使用了两台真实发动机,在向下倾斜45°的试验台上进行了8次真实介质下的预冷试验,其中6次进行了模拟任务剖面的预冷和点火试验。试验表明,某型氢氧火箭发动机射前预冷由增压预冷改进为大流量自流预冷的方案是可行的,改进后预冷时间能够满足发射流程的要求,可以最大程度上避免液氧供应管路发生"间歇泉"不稳定现象。通过模拟任务剖面进行预冷试验,表明发动机点火前氢、氧系统均能达到预冷好条件,但氧涡轮端轴承后温度比改进前偏高。6次点火试验表明,改进后的射前预冷方案未对发动机点火、起动过程造成明显影响。     

CO_2-C_3H_8复叠低温预冷系统的理论分析及优化设计

设计了一个低温级带回热器的CO2-C3H8复叠制冷循环低温预冷系统(213 K),并进行了低温预冷系统的参数选择和优化设计.该系统高温级循环采用CO2、低温级循环采用C3H8作为循环工质.通过对该系统的理论计算,得出了中间温度、复叠温差及低温级蒸发器冷端温差对系统性能系数的影响曲线;通过进一步的优化分析获得了系统最佳中间温度及对应的系统性能系数COP与复叠温差-低温级蒸发器冷端温差以及制冷温度-冷凝温度的关联式.     

差压预冷外部遮挡开孔方式数值研究及实验验证

为解决目前果蔬差压预冷的存在的降温不均匀性,设计了五种不同的外部遮挡开孔方式,包括32个均匀孔、32个非均匀孔、28个孔、40个孔及50个孔,建立了物理和数值模型,利用计算流体动力学(CFD)软件对土豆分别进行了五种开孔方式的数值模拟研究.对比分析了五种开孔方式的预冷模拟结果,预冷降温速率最快和均匀性最好的是32个非均匀孔的,并对此进行了实验验证,二者基本吻合.为差压通风预冷的外部遮挡或包装的开孔设计提出了建议:靠近压差风机处的开孔率要低以阻挡靠近差压风机侧气流,远离差压风机处开孔率要高,最底部的孔径应稍大于上部的.     

带引射循环的HFC134a气体水合物蓄冷实验研究

气体水合物蓄冷是一种安全高效的、适用于空调工况的蓄能技术,为加快HFC134a气体水合物的生成速度,采用一种新型引射器装置来增强反应物混合和扰动.通过对有引射循环与无引射循环两种不同蓄冷工况的实验对比,证实了引射比对成核过冷度和成核引导时间有应变关系,当引射比范围在0.3～0.4之间时,引射循环能有效减小成核过冷度1.5℃,水合物生成时间缩短20～30min,最佳引射比与形成气体水合物的物质质量比接近.水的初始状态对成核过冷度和成核时间有明显影响,形成过水合物的水再次生成水合物的成核时间缩短6～8min,成核过冷度减少1～2℃.     

低温储罐预冷过程预测

为了能输送和存储单相低温液体,保证输送管道和低温储罐的安全,预冷过程不可或缺。对预冷时间、预冷介质消耗量进行预测有利于指导实际操作。从热力学基本理论出发,采用稳态与变热导率的热力学分析方法,建立储罐预冷时间与预冷介质消耗量数学模型,推导了储罐温度随时间的变化关系,探讨进口流量与预冷时间、预冷介质消耗量之间的相互影响。将不同的计算方法相结合,指导选取最佳预冷流量。     

Cryogenic Boiling and Two-Phase Flow during Pipe Chilldown in Earth and Reduced Gravity

For many industrial, medical and space technologies, cryogenic fluids play indispensable roles. An integral part of the cryogenic transport processes is the chilldown of the system components during initial applications. In this paper, we report experimental results for a chilldown process that is involved with the unsteady two-phase vapor-liquid flow and boiling heat transfer of the cryogen coupled with the transient heat conduction inside pipe walls. We have provided fundamental understanding on the physics of the two-phase flow and boiling heat transfer during cryogenic quenching through experimental observation, measurement and analysis. Based on the temperature measurement of the tube wall, the terrestrial cryogenic chilldown process is divided into three stages of film boiling, nucleate boiling and single-phase convection that bears a close similarity to the conventional pool boiling process. In earth gravity, cooling rate is non-uniform circumferentially due to a stratified flow pattern that gives rise to more cooling on the bottom wall by liquid filaments. In microgravity, there is no stratified flow and the absence of the gravitational force sends liquid filaments to the central core and replaces them by low thermal conductivity vapor that significantly reduces the heat transfer from the wall. Thus, the chilldown process is axisymmetric, but longer in microgravity.      

An experimental study on flow patterns and heat transfer characteristics during cryogenic chilldown in a vertical pipe

In the present paper, the experimental results of a cryogenic chilldown process are reported. The physical phenomena involve unsteady two-phase vapor–liquid flow and intense boiling heat transfer of the cryogenic fluid that is coupled with the transient heat conduction inside pipe walls. The objective for the present study is to compare the chilldown rates and flow patterns between the upward flow and downward flow in a vertical pipe. Liquid nitrogen is employed as the working fluid and the test section is a vertical straight segment of a Pyrex glass pipe with an inner diameter of 8 mm. The effects of mass flow rate on the flow patterns, heat transfer characteristics and interface movement were determined through experiments performed under several different mass flow rates. Through flow visualization, measurement and analysis on the flow patterns and temperature variations, a physical explanation of the vertical chilldown is given. By observing the process and analyzing the results, it is concluded that pipe chilldown in a vertical flow is similar to that in microgravity to some extent.     

Two-Phase Flow and Heat Transfer During Chilldown of a Simulated Flexible Metal Hose Using Liquid Nitrogen

For many industrial, medical and space technologies, cryogenic fluids play irreplaceable roles. When any cryogenic system is initially started, it must go through a transient chill down period prior to normal operation. Chilldown is the process of introducing the cryogenic liquid into the system, and allowing the system components to cool down to several hundred degrees below the ambient temperature. The chilldown process is an important initial stage before a system begins functioning. The objective of this paper is to investigate the chilldown process associated with a flexible hose that was simulated by a channel with saw-teeth inner wall surface structure in the current study. We have investigated the fundamental physics of the two-phase flow and quenching heat transfer during cryogenic chilldown inside the simulated flexible hose through flow visualization, data measurement and analysis. The flow pattern developed inside the channel was recorded by a high speed camera for flow pattern investigation. The experimental results indicate that the chilldown process that is composed of unsteady vapor-liquid two-phase flow and phase-change heat transfer is modified by the inner wall surface wavy structure. Based on the measurement of the channel wall temperature, the teeth structure and the associated cavities generally reduce the heat transfer efficiency compared to the straight hose. Furthermore, based on the measured data, a complete series of correlations on the heat transfer coefficient for each heat transfer regime was developed and reported.     

短玻璃纤维增强聚合物注塑充填过程及纤维取向数值模拟

基于Hele-Shaw理论及广义非牛顿流体本构方程,建立了纤维增强聚合物三维薄壁注塑成型充填阶段数学模型,根据Folgar-Tucker取向模型,建立了纤维取向张量模型。采用Moldflow对拉伸试样的注塑流动过程进行模拟,研究纤维含量f和纤维间相互作用系数Ci对纤维取向的影响。结果表明,随着Ci增大,平均纤维的取向性呈减小的趋势;试样不同部位的纤维取向不同;f对纤维取向性影响较小,且存在一个最佳含量百分比数值。     

润滑油循环率对活塞式制冷压缩机性能影响的实验研究

论文用实验的方法研究了润滑油循环率对活塞式制冷压缩机工作性能的影响。为了确保实验分析的准确性,测试系统采用了双油分的装置,使排气后的制冷剂和润滑油尽量完全分离,制冷剂以纯冷媒的形式再次进入压缩机的吸气。实验中采用Sanyo某型号压缩机进行测试,其结果表明润滑油循环率随着压缩机注油量的增加而增加,油循环率对压缩机的制冷量、功率、COP以及排气温度均有影响,较低的油循环率使得压缩机具有较高的制冷量和COP,同时排气温度也比较高,较高油循环率则使压缩机的制冷量和COP下降。因此一定要选择与压缩机相匹配的注油量,控制油循环率在一个合理的范围内,这样既能使润滑油起到有效的润滑作用,保证压缩机正常工作,又能使压缩机获得最佳的性能指标。     

基于综合关联度的注塑成型工艺参数多目标稳健设计

针对注塑成型过程中的多个质量指标,提出了基于综合关联度、Kriging模型及混合交叉变异蚁群算法的注塑成型工艺参数稳健优化方法.首先给出了综合关联度的定义及计算方法,再给出了Krging模型的拟合方法和混合交叉变异的蚁群算法;在多目标稳健设计建模中,各分目标采用质量工程中的6σ原则;在混合交叉变异的蚁群算法中,提出了基...     

双尺度纤维织物二维非饱和流动的数值模拟与实验

液体模塑成型工艺(LCM)中非饱和流动的填充模拟对于在虚拟空间中快速、高效地优化工艺参数具有重要意义。采用了一种模拟双尺度纤维织物在等温条件下非饱和流动的双尺度计算模型,通过引入沉浸函数求解宏观-微观流动控制方程组,同时考虑了在微观浸渍中毛细压力的影响,在有限元/控制体积算法中实现了对非饱和流动的数值模拟。随后对三向缝合纤维织物进行了二维径向填充实验,将实验结果与数值模拟的预测值对比。结果表明,该计算模型可以较精确地模拟双尺度纤维织物中的非饱和流动。在此计算模型的基础上,讨论了流体黏度、注射流量及纤维束孔隙率对非饱和填充浸润的影响。结果表明,不同流体黏度、注射流量及纤维束孔隙率对纤维织物填充过程中非饱和区域长度、入口压力曲线及填充时间影响不同。研究结果可以对合理预测纤维织物的浸润及树脂填充过程中入口压力提供指导。     

Effect of system of initiators on the process cycle of nonisothermal resin transfer molding – Numerical investigation

The role of initiators with different reactivities on the process cycle of nonisothermal resin transfer molding (RTM) was examined using the numerical simulation. A new process model was developed based on flow, heat and mass transfer equations combined with an appropriate mechanistic kinetics model which elucidates the functions of the initiators in the system. The process cycle of RTM with both single initiator and dual-initiator (combination of two initiators) was analyzed. The numerical simulations revealed that the single initiator with high reactivity reduces the cycle time, but there is a risk of incomplete mold filling and nonuniform temperature distribution. For dual-initiator system different scenarios of initiators injection including premixed initiators, switching the initiator at a given cavity filled fraction and ramped injection of highly reactive initiator were examined. It was found that the dual-initiator system leads to reduced cycle time and improved temperature distribution with no risk of incomplete filling.     

Modeling of a novel spool compressor with multiple vapor refrigerant injection ports

A model of a novel rotary spool compressor has been developed to explore the effect of multiple injection ports on compressor and cycle performance. The thermodynamic model includes the effects of heat transfer and leakage and is numerically solved to predict the compressor power consumption and mass flow rate. Saturated vapor injection is modeled assuming that the injection pressures and the timing of the injection process can be controlled.The model predicts that adding a single injection port will provide a 12% increase in the cycle coefficient of performance (COP) when the compressor runs at 1907 rpm with R-22 evaporating at ?7 °C, condensing at 49 °C, and 15 °C of superheat. Adding a second, non-optimized injection port increases the COP by 16% compared to the cycle without injection. The model is used to investigate the effect of injection pressure, port location, and port diameter on cycle performance.