橡胶颗粒振动流化床中流体力学行为的研究

为了探讨振动流化床中颗粒的流体力学行为,在振动流化床常温实验装置上,以橡胶颗粒为试料,研究了较低开孔率下振动强度、床层高度、气速等参数对振动流化床床层压降的影响.分析了起始流态化速度随床层高度和振动强度改变的变化规律.并把实验结果同文献中尼龙1010的实验结果进行了对比,得到了有益的结论.对橡胶颗粒振动流化床中流体力学行为的研究可为低温粉碎中橡胶颗粒的低温气固传热研究给出合理的建议.     

微重力条件下泡沫复合相变材料蓄热装置数值仿真

相变材料由于相变过程中吸收或者释放大量能量且过程近似等温这一特性而有巨大的应用潜力,将相变材料蓄热装置应用于航天器是维持航天器内各个单元工作温度的一种有效方法.提出一种基于正二十烷的相变蓄热结构方案,分别填充泡沫铜与泡沫碳作为基体材料来强化相变材料的传热性能.通过对该模型进行数值仿真计算,得到相变蓄热装置温度、固液相界面位置随时间的变化等有效数据,分析泡沫相变蓄热材料在微重力条件下相变界面的演变过程.结果显示,得益于其较高的导热系数,泡沫复合相变材料可将热源热量有效分散到其他区域,减缓热源面温度上升速度,并且降低重力变化对传热的影响.所得数据结果为泡沫复合相变材料的工程应用提供了科学依据.      

航天器舷窗区域的热控设计和理论分析

结合舷窗的热设计原则,提出舷窗区域的热控设计方案。其中,重点对通过热管技术和高导热材料技术来实现等温化进行了说明,并分析了舷窗法兰框在不同传热方向上的等效导热系数。最后,对航天器舷窗区域在轨飞行的典型传热变化过程建立数学模型,并给出其简化的理论解。     

真空同心管套的热分析

真空同心管套涉及传导、辐射等传热方式,其中低压气体的热传导非常复杂,是分析问题的关键。对处于不同隔热措施的真空同心管套内辐射换热和气体导热予以准确的描述,建立了传热模型。并在考虑材料真空放气的情况下,计算了管套的当量导热系数。所用方法和技术可用于空间热物理等领域中类似问题。     

塞式热流传感器影响因素的分析计算

介绍了塞式热流传感器的结构及测量原理。针对传感器敏感元件的形状尺寸,隔热层材料的导热系数、比热容以及两种材料的表面发射率等一系列影响测量结果的因素,利用Fluent软件对各种模型进行了传热仿真,分析了各种因素对测量结果的影响,为传感器的研制提供依据和指导。     

纳米复合相变材料熔化过程数值模拟

相变储能技术在航空航天等领域具有广泛的应用前景,但是相变材料导热性能差制约了其工程化应用。高导热的纳米材料能够有效提高相变材料的导热性能。为了对其相变现象进行更精细的模拟分析,基于Maxwell-Garnett等效介质理论（EMT）建立3种具有代表性结构的纳米复合相变材料详细物性参数,将流体体积（VOF）模型与焓-多孔介质模型相耦合,在考虑相变材料体积膨胀的情况下,数值模拟了纯石蜡、添加不同体积组分金刚石纳米粒子（ND）、单壁碳纳米管（SWCNT）和石墨烯纳米片（GnP）的纳米复合相变材料在定温边界条件下的固液相变过程。结果表明:相变材料熔化过程中对流效应主要分布在临近固液相界面、临近加热壁面及临近气液两相交界面这3个区域;3种纳米粒子中GnP的导热强化效果最佳,相比纯石蜡,添加体积分数为3%的GnP纳米复合相变材料固相导热系数提高了486%,相变材料的熔化时间缩短了69%;升高壁面温度能够有效缩短复合相变材料的熔化时间。      

自然对流对相变材料熔化过程的影响分析

为分析自然对流对相变材料熔化过程的影响,建立了二维瞬态、固/液相统一的控制方程,采用SIMPLE算法对底部加热、顶部冷却的方腔内相变材料熔化过程进行了数值仿真,研究了方腔内温度场和速度场随时间变化规律,结果表明:自然对流使液相区等效导热系数增大;随着固液界面向上移动,液相区自然对流逐渐增强,流动状态不断变化.     

轴向通流旋转盘腔流动换热稳态实验与数值模拟

通过开展稳态实验及数值模拟探究了轴向通流旋转盘腔的流动结构与换热特性。通过改变流量系数、旋转雷诺数等参数,探究不同工况下旋转盘两侧及盘罩内侧壁面温度和努塞尔数的径向分布规律。结果表明:在轮缘加热的状态下,旋转盘两侧温度径向分布均呈凹函数形态,且旋转盘迎风面换热强度普遍高于背风面;后轴颈盘罩向两端旋转盘导热,其壁面温度径向分布呈"中间高、两侧低"的状态;随着轴向流量系数的增大,盘腔内部气体对流加剧,径向臂及涡对结构更加明显,旋转盘及轴颈表面换热效果增强;旋转盘腔内的流动换热特性受强迫对流和类Rayleigh-Benard对流2种机理的共同影响。      

计及壁面传热的微型向心涡轮气动设计探讨

毫米级微型向心涡轮传热效应显著区别于常规向心涡轮,发展计及壁面传热效应的微型向心涡轮的气动设计方法对微型燃气轮机的设计具有重要意义.根据微型向心涡轮壁面非绝热的特点,通过理论分析,初步建立了计及固壁传热效应的微型向心涡轮速度三角形的分析模型.在此基础上发展了计及传热效应的微型向心涡轮的气动设计方法.分析得到了考虑传热影响的微型向心涡轮设计规律.利用三维数值模拟手段对模型和设计方法进行了验证.结果初步表明所发展计及壁面传热效应的模型和微型向心涡轮气动设计方法具有较好的可行性.     

旋转状态下涡轮叶片前缘的流动与换热

用数值模拟的方法对旋转状态下涡轮叶片前缘冷却结构进行了数值研究,该结构由进气腔、叶片尾缘块和前缘块构成,对此结构不同的旋转速度情况进行了计算,根据计算结果分析了旋转对涡轮叶片前缘流动与换热的影响.计算结果表明,旋转状态下带气膜出流的冲击流动中,前尾缘冲击面的换热随着转速的增加而减小,且尾缘冲击面的换热比前缘冲击面的换热要好;同时前尾缘冲击面换热的差别随着转速的增加将越来越小.     

Integrated design of solar thermal propulsion system for microsatellite with liquid ammonia as propellant

This paper presents a design of solar thermal propulsion (STP) system for microsatellite with liquid ammonia as propellant. The system was equipped with two concentrators, which were respectively placed in the tank and thrust chamber for propellant supply and heating. A platelet heat exchanger was adopted to heat the propellant in the chamber, and the fluid–solid coupling effect between the wall and the gas was considered. Meanwhile, the effects of satellite mass, initial orbit, nozzle size and target temperature on the performance of STP system were analyzed. The results show that for microsatellites with a total mass of 100 kg, the STP system can fully heat the propellant to more than 2050 K, generate an intermittent thrust of about 26 N, and enable the satellite to obtain a velocity increment of more than 1470 m/s within 19 days, consuming only 42 kg of propellant, which can directly meet the transfer mission from the geostationary transfer orbit (GTO) to the geostationary orbit (GEO). The maximum velocity increment could reach more than 1950 m/s when the propellant was completely consumed; Changing the mass and initial orbit of the satellite will not affect the thrust and specific impulse. Satellites with smaller mass will spend less time and propellant during orbit transfer. The lower is the perigee height of the initial orbit, the greater is the propellant consumption, while the shorter is the time of orbit transfer; The reduction of nozzle throat size and target temperature will lead to the increase of specific impulse and the decrease of orbital transfer time, but the reduction of thrust.     

Self-similar flow of a rotating dusty gas behind the shock wave with increasing energy, conduction and radiation heat flux

A self-similar solution is obtained for one dimensional adiabatic flow behind a cylindrical shock wave propagating in a rotating dusty gas in presence of heat conduction and radiation heat flux with increasing energy. The dusty gas is assumed to be a mixture of non-ideal (or perfect) gas and small solid particles, in which solid particles are continuously distributed. It is assumed that the equilibrium flow-condition is maintained and variable energy input is continuously supplied by the piston (or inner expanding surface). The heat conduction is expressed in terms of Fourier’s law and the radiation is considered to be of the diffusion type for an optically thick grey gas model. The thermal conductivity K and the absorption coefficient α_R are assumed to vary with temperature only. In order to obtain the similarity solutions the initial density of the ambient medium is assumed to be constant and the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. The effects of the variation of the heat transfer parameters and non-idealness of the gas in the mixture are investigated. The effects of an increase in (i) the mass concentration of solid particles in the mixture and (ii) the ratio of the density of solid particles to the initial density of the gas on the flow variables are also investigated.     

涡轮叶片尾缘复合通道的换热

采用热色液晶测温法,测量了涡轮叶片尾缘带隔板的复合通道的温度场,分析了射流冲击强化扰流柱通道内换热的机理,讨论了两通道间隔板的不同开孔结构对换热的影响.从工程应用的角度出发提出了几个换热评价指标,对不同开孔结构的隔板进行了换热评价.结果表明:冷气由第1通道进入,通过隔板上的孔不断由径向流动变为弦向流动后,对第2通道的扰流柱区形成冲击,最后由劈缝排出,提高了尾缘的换热;开孔均匀的隔板换热效果相对较好.     

丙烯环路热管补偿器的可视化实验研究

通过采用石英补偿器和高速摄像机实现了对丙烯环路热管补偿器的可视化实验研究，重点研究了补偿器内工质的状态随充装量和传热量的变化及充装量对环路热管传热性能的影响。研究发现，容积为51.4 mL的环路热管最佳充装量约为19.7 g。充装量小于最佳充装量的各工况下，能观察到对应补偿器内工质液面高度低于引流管，蒸发器和补偿器之间相变换热强烈，引流管外壁面明显有工质的冷凝及流动，且工质冷凝和流动的速度随着传热量的增加而加快；随着充装量增加，环路热管传热热阻减小，280 K工作温度以下的传热量增大。最佳充装量对应的补偿器内液面高度浸没引流管而接近蒸发器核心通道顶端，得到280 K以下最大传热量为40 W，对应的最优传热热阻为2 K/W。充装量大于最佳充装量的工况下，补偿器内液面高度超过蒸发器核心顶端，随着充装量增加，环路热管传热热阻增大，280 K以下的传热量减小。补偿器和蒸发器核心通道内的工质分布能影响蒸发器向补偿器的漏热量，这是充装量影响环路热管性能的重要原因。      

矩形通道中亚尺度肋片的流动换热数值分析

对装有不同结构亚尺度肋片矩形通道的流动和换热进行了数值模拟,获得了通道流场、温度场分布以及平均努塞尔数的基本特征,对各种肋片通道的换热特性进行了对比分析.计算结果表明:亚尺度肋片距主肋片根部越近越有利于散热;在远离热面区域,亚尺度肋片的比表面积越大传热效果越好.当扩展表面积相同时,亚尺度肋片的长宽比越大换热效果越好;计算结果及分析揭示了控制肋片最优几何形状的统一原则——广义温度梯度均匀化原则,并依照此原则确定了可以强化换热的较优的肋片结构.计算分析表明广义温度梯度均匀化原则可以控制对流换热过程的传热强化.      

Magnetogasdynamic shock wave generated by a moving piston in a rotational axisymmetric isothermal flow of perfect gas with variable density

The propagation of a strong cylindrical shock wave in an ideal gas with azimuthal magnetic field, and with or without axisymmetric rotational effects, is investigated. The shock wave is driven out by a piston moving with time according to power law. The ambient medium is assumed to have radial, axial and azimuthal component of fluid velocities. The fluid velocities, the initial density and the initial magnetic field of the ambient medium are assumed to be varying and obey power laws. Solutions are obtained, when the flow between the shock and the piston is isothermal. The gas is assumed to have infinite electrical conductivity and the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. It is expected that such an angular velocity may occur in the atmospheres of rotating planets and stars. The shock wave moves with variable velocity and the total energy of the wave is non-constant. The effects of variation of the initial density and the Alfven-Mach number on the flow-field are obtained. A comparison is also made between rotating and non-rotating cases.