航天用纳米流体流动与传热特性的实验研究

研究航天用纳米流体流动与传热特性。测量了不同粒子体积份额的航天用纳米流体雷诺数500~4000范围内的管内对流换热系数和摩擦阻力系数,详细讨论了雷诺数和纳米粒子体积份额对纳米流体对流换热系数和摩擦阻力系数的影响,分析了航天用纳米流体的强化传热性能。实验结果表明,在液体中添加纳米粒子增大了液体的管内对流换热系数,增加了液体的传热效果,粒子的体积份额是影响纳米流体对流换热系数的因素之一,在相同雷诺数条件下,纳米流体的对流换热系数随粒子体积份额的增加而增大。与原液体工质相比,航天用纳米流体的流动阻力系数稍有增大,纳米流体的流动阻力系数不随纳米粒子的体积份额而变化。与航天用纳米流体对流换热系数的增加相比,纳米流体流动阻力系数增大的程度极小,验证了纳米流体强化传热技术应用于航天器热控系统的可行性。     

预旋结构对空间布雷顿循环涡轮盘表面换热特性的影响

针对空间核动力航天器涡轮盘表面温度过高和温度梯度较大的情况，提出了一种预旋涡轮盘冷却结构。采用数值模拟的方法对比分析了有无预旋2种冷却结构下的涡轮盘表面换热特性，研究了旋转雷诺数对换热效果的影响。计算结果表明:与无预旋结构相比，预旋结构可以有效地提高氦氙冷却气流与涡轮盘的对流换热系数，降低其表面最高温度和温度梯度，最高温降可达63.1 K。随着旋转雷诺数增大，涡轮盘表面最高温度降低，轮盘表面平均换热系数增大，采用预旋结构的表面平均换热系数比无预旋结构增大13.4%。     

氧化剂质量通量对固液火箭发动机中固体燃料退移速率的影响

针对采用硝酸/HTPB型推进荆的固液混合火箭发动机,采取数值方法研究了氧化剂质量通量对固体燃料热解表面退移速率及换热的影响.研究表明,固体燃料热解表面轴向平均对流换热热流密度、总热流密度以及退移速率与氧化荆质量通量的n次方近似成正比,n的值介于0.6～0.7之间;固体燃料热解表面的辐射换热热流密度近似与氧化刺质量通量成正比;随着氧化剂质量通量的增加,辐射换热占总换热量的比例逐渐增加,增加幅度逐渐减小.     

预冷发动机氢氦PCHE通道换热与热应力数值分析

基于高超声速预冷发动机闭式氦布雷顿循环中印刷电路板换热器(PCHE)的应用,对PCHE氢氦通道的热固耦合特性进行了数值研究,着重阐述了热侧氦参数对换热的影响机制。探究了热侧壁温和换热系数的变化特征及其对冷侧换热的影响。考察了通道截面温度和湍动能的分布情况。通过熵产和综合换热系数评价了PCHE通道的性能,进行了通道热应力分析,建立了热侧和冷侧换热关联式(误差在±15以内)。结果表明:热侧压力对换热仅有微弱影响;热侧流量提高对热侧和冷侧换热均有增强作用。热侧进口温度下降导致热侧和冷侧换热减弱;热侧进口温度提高造成通道熵产显著增加,热侧流量增加造成通道熵产显著减小;高热应力出现在冷热流道之间和壁面两侧,局部最大热应力达到25 MPa。     

蜂窝板预埋管路辐射器流动散热特性仿真

为解决传统数值方法对辐射器对流换热系数评估困难、流动散热性能预测精度不高的问题,明晰工况参数与重力对辐射器流动散热特性影响规律,指导辐射器轻量化设计与地面试验,构建辐射器导热-对流-辐射耦合传热等比仿真模型,评估其与经验公式对辐射器水动力及热特性预测可靠性,分析流量、入口温度、吸收外热流及重力对辐射器工作特性影响规律。结果表明:辐射器压降及散热功率模拟值与真空热试验数据最大相对误差为3.45%和2.86%,压降及换热系数经验公式预测值与仿真值最大相对误差为-10.15%和-33.18%;辐射器散热功率随流量与入口温度的增加而增大,吸收外热流增加会降低对流换热热流量,相较零重力,常重力水平状态辐射器散热功率提高2.86%。所建模型可准确预测辐射器工作特性;辐射器设计应在满足压降与出口温度指标要求时,提高流量与入口温度,地面试验辐射器应竖直放置。     

吸热型碳氢燃料再生冷却性能评估方法

吸热型碳氢燃料作为吸气式高超声速飞行器的再生冷却剂,冷却剂出口温度可达到750℃以上。碳氢燃料的冷却能力和抗结焦特性指标,是再生冷却剂的关键参数。在工程应用参数范围内,建立了吸热型碳氢燃料再生冷却性能综合评估体系,实现燃料热沉、结焦和流动传热性能的综合评估。燃料热沉采用热平衡法测量。作为参考:燃料温度600℃,热沉约2.0 MJ/kg;燃料温度750℃,热沉约3.5 MJ/kg。结焦采用层流流动阻力法进行定量测量,应用泊肃叶定律计算碳氢燃料结焦前后通道的当量内径,从而得到通道内结焦层的平均厚度。流动换热性能的评估方法是比较相同出口流体温度条件下不同燃料壁面温度沿轴向的分布趋势。以上吸热型碳氢燃料评估方法的建立,为研制吸热型碳氢燃料提供了有效的初步筛选途径。     

储液器在被动式热交换下环路热管的热性能研究

环路热管是应用于航天器、航空器、舰船等设备的新型换热器件,热性能是评价环路热管的主要性能参数。通过试验和系统级数值模拟研究了当储液器处于自然对流的被动式热交换时,环路热管在不同冷源温度下的温度分布特性和换热性能,说明环路热管总热阻和冷凝器利用率受冷源温度的影响规律。环路热管存在可变热导和固定热导区:在可变热导区,环路热管总热阻随热负荷的增大迅速减小,而升高冷源温度有助于降低总热阻;进入固定热导区后,总热阻则趋于稳定。蒸发器换热系数随着热负荷的增大先增大后减小,但其变化幅度在冷源温度较高时明显减弱。     

考虑对流换热影响的固体发动机热力耦合分析

考虑壳体与空气自然对流换热的影响,对固体发动机结构进行了热力耦合有限元分析。研究了对流换热对发动机结构响应的影响,讨论了不同对流换热系数下的温度及应变响应变化规律,评估了某双伞盘固体发动机经历固化降温、低温试验及低温贮存过程的结构完整性。结果表明,考虑对流换热能更准确地反映发动机的受载状态;对流换热系数变化影响其结构响应历程,但随对流换热系数的不断增大,这种影响逐渐减弱。     

肋参数对液氧甲烷发动机推力室强化换热的影响

为深入研究带肋推力室强化传热的机理，对带肋液氧/甲烷推力室的燃烧与再生冷却进行了流动与传热耦合分析，并针对不同肋高和肋数目进行了参数化分析。结果表明:引入等效平均热流密度的概念可以准确描述带肋推力室中的实际传热过程;平均热流密度总是随着肋数目的增加而减小，当肋高恒定时，由于总换热面积增大，等效平均热流密度会随着肋数目的增加而增大;而当总表面积恒定时，等效平均热流密度会随肋数目的增加而减小。此外，盲目地增大总换热面积并不一定能改善传热强化，甚至会在某些情况下恶化传热，因此在设计过程中也应该结合其他肋参数进行综合考虑。     

航天热防护材料的烧蚀特性研究

介绍了运用 CO_2激光加热装置,对聚四氟乙烯(Teflon)和热防护烧蚀材料 AT2的烧蚀特性研究.研究发现聚四氟乙烯的烧蚀率随热流的上升而增加;随氮气压强和流量的上升而下降;烧蚀过程产生的凝胶区和激光支持气相火焰区,与热流、环境气体种类及压强有关,凝胶区厚度随热流上升而下降,当热流很高时,却趋于一个常数;烧蚀表面温度随热流上升而升高,在本研究条件下,在600～700℃之间.AT2材料的温度和碳化层厚度,随加热时间而增大,随氮气压强的增加而减小.对入射激光束反射强的表面,碳化时的最大温度较低,碳化层的厚度较小.     

不同压力条件下水平平板的表面换热实验研究

为了解不同压力下水平平板的气体对流换热变化情况,搭建了一个提供不同气压和环境温度的实验舱,开展了在不同压力(0.1 Pa、0.1 k Pa、0.2 k Pa、0.5 k Pa、1 k Pa、10 k Pa、50 k Pa和常压)与几种加热量(75、150、300 W/m~2)组合条件下的水平平板换热实验研究。通过对辐射换热和自然对流换热的比较,得到不同压力下气体的对流换热系数。结果表明:对流换热系数在环境气体压力小于1 k Pa时非常小,而在1 k Pa以上时才较大;在大于1 k Pa时,对流换热系数随压力的升高呈二次方增加。     

Buoyancy effects on smoldering combustion

A theoretical and experimental study is carried out to determine the effect of buoyancy on the rate of spread of a cocurrent smolder reaction through a porous combustible material. Since buoyant forces are proportional to the product g(_gi − _g), they can be controlled experimentally by varying either the gravitational acceleration, g, or the density difference, _gi − _g. The latter approach was followed in the present work. Measurements are performed of the smolder spread rate through porous α-cellulose (0.83 void fraction) as a function of the ambient air pressure. The experiments are carried out in a pressure vessel for ambient pressures ranging from 0.5 to 1.2 atm. The rate of spread was obtained from the temperature histories of thermocouples placed at fixed intervals along the fuel centerline. The smolder velocity was found to increase as the ambient pressure was increased. Extinction was found to occur when the buoyancy forces could not overcome the drag forces, indicating that at least for the present experimental conditions transport by diffusion cannot, by itself, support the spread of a smolder reaction. This conclusion is particularly important for outer space conditions where gravity and consequently buoyancy could be negligible. In the analysis, which assumes one-dimensional processes, the transport equations are solved to give the smolder spread rate as a function of the inlet oxygen mass flux. This mass flux is then estimated by balancing buoyancy and drag forces. Assuming that the smolder chemical reaction is only weakly dependent on pressure, the analysis finally predicts a smolder velocity dependence of the form v Y_oig²_gi Pa², i.e. is proportional to the ambient pressure squared. Good qualitative agreement is found between the theoretical predictions and the experimental results.     

太阳电池对平流层飞艇热特性的影响分析

研究太阳电池对平流层飞艇驻空阶段热特性的影响。建立了太阳电池热模型、平流层飞艇热分析模型，包括热平衡方程、太阳直射辐射、天空散射辐射、地面反射辐射、大气长波辐射、地球长波辐射、蒙皮长波辐射、对流换热等；采用多节点模型，对平流层飞艇在驻空期间太阳电池、蒙皮与艇内氦气温度变化过程进行了数值模拟，得到了温度昼夜变化规律；分析了太阳电池（含隔热结构）的等效面积热阻、转换效率、铺装面积对平流层飞艇热特性的影响，得到了其温度昼夜变化规律。本文为平流层飞艇热性能分析和热控系统设计提供依据。     

Order of magnitude analysis of convective effects in dendritic solidification

The different types of convective phenomena which may occur during the dendritic solidification of metallic alloys are discussed from an order of magnitude analysis. Bulk thermal convection and/or interdendritic solutal convection have to be considered according to the values of the experimental data. Scaling laws for the solute boundary layer resulting from bulk thermal convection have already been derived. It is shown here that the interdendritic flow depends on a solutal Grashof number Gr based on the horizontal density gradient and a characteristic length L_s which is of the order of the liquid channels width. For Gr < 1, which is generally verified in practical cases, the interdendritic flow velocity U_r is proportional to the Grashof number. This a priori law compares favorably with the results of horizontal solidification experiments where the mean interdendritic flow velocity has been estimated from the resulting measured macrosegregation. In these experiments, as well as for most horizontal dendritic solidifications of metallic alloys at 1 g, the ratio $\text{U}{}_{\mathrm{r}}\text{R}$ (R is the growth rate) is of order one. In order to cancel the interdendritic flow effects, this ratio has to be lowered by one order of magnitude. According to our analysis, this can be obtained by performing the experiments either at a slightly reduced g level (～10^?1 g), or at 1 g in a vertical stable configuration with a sufficiently low residual horizontal thermal gradient.     

液氧／煤油发动机煤油高低温试验工艺技术

为了进行液氧／煤油发动机煤油高低温试验,试车台必须具备煤油换热能力,掌握换热工艺。通过分析和比较,确定了煤油换热系统的组成、换热方法及煤油中游离水的去除方法。介绍了煤油换热的时间安排、煤油升温和降温的工艺过程、换热用煤油的流量调节及温度控制要求。提出了试车前煤油温度的保证方法、系统调试及模拟试验的实施效果评定方法。     

Modeling the Modification of the Nighttime High-Latitude F-Region by Powerful HF Radiowaves

A mathematical model of the high-latitude F-region, taking the ionospheric plasma convection into account, is used for modeling a response of the auroral F-region to irradiation by powerful high-frequency (HF) radiowaves. The model enables us to calculate the time variations in the profiles of the electron concentration, the velocity of positive ions, and the ion and electron temperatures in the part of a magnetic-flux tube moving over an artificial ionospheric heater under the action of a convective electric field. The modeling was carried out for a part of the magnetic flux tube intersecting the F-layer irradiated by the Norwegian heater at Tromsö when it is located near the midnight magnetic meridian. The calculations were made for the equinox conditions under the high solar and low geomagnetic activity. The results of our modeling show that substantial variations in the profiles of the electron temperature, the velocity of positive ions, and the electron concentration can be produced in the nighttime high-latitude F-layer due to HF heating. The perturbation caused by a 20 s rectangular pulse should exist for about 20 min at the level of the F-layer maximum. The disturbed plasma volume can leave the region irradiated by the heater and move away for over 500 km within the above-mentioned time period.     

Analytical comparison of condensing flows inside tubes under Earth-gravity and space environments

The heat transfer behavior of flow condensation inside horizontal tubes under zero-gravity and Earth-gravity conditions is modelled and analyzed. For Earth conditions for wetting fluids the annular flow region changes to a stratified flow pattern owing to gravity drainage of the condensate from the upper portion of the tube. The stratified condensate layer is considered inactive in the heat transfer process; its magnitude is determined along the tube length using the analytical results of Rufer and Kezios. Under zero-gravity conditions no such gravity drainage occurs and so the flow is considered to be annular along the complete length of the tube. The analytical approach of Bae was used to evaluate the heat transfer rates under zero gravity conditions. The results indicate a substantially poorer condensing performance under zero-gravity conditions. These results can be simply explained in terms of the smaller condensate film thickness over the upper portion of the tube periphery at any axial location under earth-gravity conditions because of gravity drainage of the condensate.     

Surface temperature distribution along a thin liquid layer due to thermocapillary convection

The surface temperature distributions due to thermocapillary convections in a thin liquid layer with heat fluxes imposed on the free surface are investigated. The nondimensional analysis predicts that, when convection is important, the characteristic length scale in the flow direction L, and the characteristic temperature difference ΔT₀, can be represented by and , respectively, where L_R and ΔT_T are the reference scales used in the conduction-dominant situations with A denoting the aspect ratio and Ma the Marangoni number. Having had L and ΔT₀ defined, the global surface-temperature gradient ( ), the global thermocapillary driving-force, and other interesting features can then be readily determined. Finally, numerical calculations involving a Gaussian heat flux distribution are presented to justify these two relations.     

新型高密度燃料性能研究

研究了新型高密度碳氢化合物HD-2与航空煤油的复配。通过对不同配比的燃料的密度、黏度、闪点、燃烧热值的测定比较,研究了复配燃料的基本性能;通过火箭一冲压组合发动机（RBCC）航空煤油点火燃烧性能实验,研究了不同HD-2添加含量的复配燃料的燃烧性能。基本性能测试实验和点火燃烧性能实验的结果表明：添加HD-2高密度碳氢化合...