航天器热辐射器MMOD击穿泄漏特性分析及验证

针对空间站等长寿命载人航天器热辐射器在舱外受微流星体和空间碎片(MMOD)击穿后工质泄漏导致的热控系统失效风险问题,文章对热辐射器被击穿后漏孔的泄漏特性进行了分析,建立了数学计算模型,计算得到了漏孔孔径与泄漏容积速率关系。通过试验,验证了数学模型的准确性,结果表明:当泄漏孔径≤3 mm时,泄漏数学模型能够很好的预测泄漏的速率、压力等特性。可以为应用流体回路热辐射器进行热量排散的低轨航天器设计提供参考。

钨热辐射器电化学抛光试验研究

钨热辐射器是热光伏系统中的重要单元,热光伏技术的发展对钨热辐射器表面质量的要求变得更高。为提高钨金属表面质量,基于电化学抛光原理构建了一套电化学抛光装置,通过单因素试验探究了工艺参数对电化学抛光表面质量的影响规律。结果表明:电化学抛光表面粗糙度随着抛光加工电压、加工时间、加工间隙和电解液温度的增加呈现先减小后增大的趋势,最佳的工艺参数为加工电压20 V、加工时间160 s、加工间隙5 mm、电解液温度25℃,此时得到的表面抛光效果最佳。

微结构热辐射器光谱特性的影响因素研究

针对热光伏系统的热辐射器表面设计的问题,基于微结构的波长选择控制理论,利用FDTD方法对周期性表面微腔结构进行数值模拟计算,将模拟结果与文献数据对比验证了本文模型的正确性。围绕周期性金属腔体微结构,分析了腔体尺寸大小、周期大小对腔体微结构吸收光谱的影响;分析了周期大小对、钼、镍、铂、铜、银、金几种金属微腔结构的吸收光谱的影响;在微小尺寸差异下,比较了钨、钼、镍、铂几种金属微结构的圆腔、方腔、六棱柱腔的吸收光谱的差异,总结出几点规律,对指导微腔结构热辐射器的设计和加工有重要的意义。

空间行波管热辐射器机械固定与焊接对比研究

为了降低辐冷空间行波管收集极温度,需要保证热辐射器与行波管收集极间有良好的热接触,尽量减小接触热阻。在设计上,热辐射器与收集极间可使用机械固定与焊接两种连接方式。本文分别介绍了这两种连接方式,讨论了两种连接方式的工艺途径以及工艺特点。从工艺特点方面比较,机械固定方式具有较明显的优越性。为进一步比较两种连接方式传导散热能力,设计并开展了热平衡试验,测量了两种连接方式的接触热阻。试验结果显示,焊接方式的接触热阻比机械固定结构小0.133K/W,具有更好的热传导能力。文中介绍的两种连接方式及相关分析与试验结论为辐冷空间行波管热辐射器与收集极连接方式设计提供了一定参考。本文创新点在于设计并实现了热辐射器与收集极两种连接方式,并首次为此设计进行了热平衡试验,比较了两种连接方式的传导散热能力。

光子晶体热辐射器在热光伏系统中的应用

提高热光伏(TPV)系统的光电转换效率是目前热光伏技术的研究重点,提高热辐射器的辐射效率是提高热光伏系统效率的重要途径,而光子晶体结构以其特有的选择性辐射性能成为热光伏系统理想的热辐射器。简述了热光伏系统的工作原理及光子晶体的物理特性,重点介绍了光子晶体热辐射性能及其在热光伏系统中应用研究的进展情况。

一维光子晶体热辐射光谱控制模拟研究

将一维金属-介质光子晶体应用于热辐射光谱控制,基于电磁波理论建立了光谱能量关系和光谱特性计算方法。采用钨(W)和二氧化硅(SiO_2)设计了一维金属-介质光子晶体,从麦克斯韦方程组出发,研究了该一维结构的光谱特性。研究结果表明,该结构能够有效地结合材料自身光谱属性和光子晶体的光谱控制特性实现热辐射光谱特性的选择控制,可被用于热光伏系统实现热辐射光谱控制。

估算空间辐射器传热效率的平均法

为了对辐射器传热效率进行有效评估,从局部肋效率公式入手,通过肋根温度和等效热沉温度的平均,获得流体回路-热管混合式辐射器的系统传热效率的解析公式.与数值计算结果进行比对分析,证明两者的偏差小于7%.该公式避免了复杂的数值计算,可用在工程计算中对空间热辐射器的系统传热效率进行评估.

Structural design and experimental research of microwave radiation heater for asphalt pavements

In order to improve the efficiency of heating and the uniformity of temperature distribution in recycling asphalt mixtures, a pyramidal radiation heater is designed. The principles of designing horn surface size and antenna length are established according to the law of energy conservation and microwave antenna radiation theory. Modeling and simulation are carried out using IE3D software. The simulation results demonstrate that, with a fixed horn surface size, the shortened electric antenna length is the main factor leading to the improved heating uniformity. On the other hand, with a fixed antenna length and diminished surface size, the standing wave ratio decreases with the improved radiation efficiency. Furthermore, the efficiency of radiation drops with increased distance between the horn surface and the asphalt pavement. Microwave heating experiments are carried out using this type of heater. The temperature distribution of asphalt samples is obtained by the grid temperature measurement method, and Matlab simulation is performed. The experimental results are in good agreement with the simulation.

Product Identification and Mass Spectrometric Analysis of n-Butane and i-Butane Pyrolysis at Low Pressure

The pyrolysis of n-butane and i-butane at low pressure was investigated from 823-1823 K in an electrically heated flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry. More than 20 species, especially several radicals and isomers, were detected and identified from the measurements of photoionization efficiency （PIE） spectra. Based on the mass spectrometric analysis, the characteristics of n-butane and i-butane pyrolysis were discussed, which provided experimental evidences for the discussion of decomposition pathways of butane isomers. It is concluded that the isomeric structures of n-butane and i-butane have strong influence on their main decomposition pathways, and lead to dramatic differences in their mass spectra and PIE spectra such as the different dominant products and isomeric structures of butene products. Furthermore, compared with n-butane,i-butane can produce strong signals of benzene at low temperature in its pyrolysis due to the enhanced formation of benzene precursors like propargyl and C4 species, which provides experimental clues to explain the higher sooting tendencies of iso-alkanes than n-alkanes.

Simulation of Solar Radiation Conditions in Coastal and Continental Areas by Using a New Algorithm

An algorithm developed at the University of Botswana is used to study solar radiation conditions in Namibia, South Africa, Mozambique and Botswana. The synoptic stations chosen for the study differ by meteorological conditions and location： some are in coastal areas and others are in continental locations. The simulation results reveal that daily direct beam solar radiation, Hbn, is usually higher in the continental area than in the coastal one. The same situation is observed with daily global solar radiation, Hg. The difference becomes even larger for partly cloudy weather, because in coastal areas sunshine hours are usually less than in continental areas. Furthermore, coastal areas have higher humidity and bigger air mass compared to continental locations. It is concluded that continental areas are more convenient for utilisation of solar energy using solar devices with concentrators （middle-temperature and high-temperature Rankine cycles）, while at coastal areas flat-plate collectors and PV-arrays are preferable. It is found out that the range of optimum slopes for SADC countries studied is from ＋30° to -62°.

Non-thermal radiation heating synthesis of nanomaterials

The nanoscale effect enables the unique magnetic,optical,thermal and electrical properties of nanostructured materials and has attracted extensive investigation for applications in catalysis,biomedicine,sensors,and energy storage and conversion.The widely used synthesis methods,such as traditional hydrothermal reaction and calcination,are bulk heating processes based on thermal radiation.Differing from traditional heating methods,non-thermal radiation heating technique is a local heating mode.In this regard,this review summarizes various non-thermal radiation heating methods for synthesis of nanomaterials,including microwave heating,induction heating,Joule heating,laser heating and electron beam heating.The advantages and disadvantages of these non-thermal radiation heating methods for the synthesis of nanomaterials are compared and discussed.Finally,the future development and challenges of non-thermal radiation heating method for potential synthesis of nanomaterials are discussed.

Structural topology optimization on sound radiation at resonance frequencies in thermal environments

Thermal and acoustic environments pose severe challenges to find optimal design that exhibits ideal acoustic characteristics the structural design of hypersonic vehicles. One of them is to in a frequency band, which is discussed in this paper through topology optimization aiming at resonance sound radiation in thermal environments. The sound radiation at resonance fre- quencies is the main component of response, minimization on which is likely to provide a satisfactory design. A bi-material plate subjected to uniform temperature rise and excited by harmonic loading is studied here. Thermal stress is first evaluated and considered as prestress in the following dynamic analysis; radiated sound power is then calculated through Rayleigh inte- gral. Sensitivity analysis is carried out through adjoint method considering the complicated relationship between stress-induced geometric stiffness and design variables. As the resonance frequency is constantly changing during the optimization, its sensi- tivity should be considered. It is also noticed that mode switching may occur, so mode tracking technique is employed in this work. Some numerical examples are finally discussed.