微型火焰管中燃烧的研究

提出了一种新型的微动力机电系统观念,即微型热光电 TPV(thermo photovoltaic)系统。微型燃烧室是微型TPV系统中最重要的部分之一。为了获得较高的能量转换效率,需要使燃烧器壁面四周处于较高且分布均匀的温度状态。尺寸效应对微型燃烧室中的持续燃烧带来了很大的影响。为了分析微型燃烧器中燃烧的可行性和有关影响因素,在不同工况下进行实验。结果表明,在一定的流量和混合比范围内,可以在微型火焰管内维持稳定的燃烧,高温能够在燃烧室四周均匀分布。     

不同工况下旋流液雾燃烧的直接数值模拟

采用有限差分方法对不同工况下三维旋流液雾燃烧进行了直接数值模拟,其中液滴的跟踪在拉格朗日框架中进行,液滴的蒸发相变采用无限热传导蒸发模型描述,气相燃烧采用自适应单步反应机理,模拟中采用的模型燃烧器尽可能逼近真实的燃气轮机旋流燃烧器.结果发现,旋流液雾燃烧流动和火焰结构受到旋流方式和当量比的影响,流场中出现了反平行排列的...     

强化管表面水降膜蒸发的实验研究

本文研究了三种强化管对降膜蒸发换热效果的影响,利用热阻分析的方法,求得不同工况下降膜蒸发的换热系数。以水为介质,实验在绝对压力为1000Pa的条件下进行。通过对换热系数与降膜流量之间关系的研究,发现随着流量的增大,降膜蒸发过程分成管壁部分干涸以及全湿润两个状态;当流量处于转变值时,降膜蒸发的换热系数达到最大值。另外结果表明,当降膜雷诺数在10～110范围内,Turbo-CAB(26fpi)管表面的降膜蒸发换热系数是光管的3～5倍;但当液膜完全覆盖Turbo-CAB的翅片时,其强化换热效果将变差。     

微型燃烧器预混腔内催化重整、积碳及流动特性模拟

因微型燃烧器内微尺度燃烧易熄火,燃烧效率不高,存在催化重整过程中的积碳、微尺度等问题,可利用甲烷和湿空气中水蒸汽预混催化重整产氢来强化燃烧,对预混腔内催化重整,积碳及流动特性进行模拟,探讨了微型预混腔中甲烷、水蒸汽重整过程中水碳比、质量流量和催化壁面温度对催化重整、积碳、流动等的影响.     

气液两相旋流燃烧的时均统计特性

通过直接数值模拟的方法研究了旋流燃烧器中三维正庚烷喷雾燃烧,为实际喷雾蒸发和燃烧问题提供参考。气相燃烧模型采用自适应单步反应机理,液相采用拉格朗日方法跟踪,液滴蒸发采用无限传导蒸发模型。本文研究了气相和液相时均特性.结果发现燃烧和中心回流区(CRZ)之间有相互促进作用;同向旋流导致更强的中心回流区(CRZ),但是会有更小的外部回流区(ORZ);富预混燃烧会有更高的化学反应速率,并且蒸发冷却的影响更为明显;湍流入流会导致更高的液滴散布和更小的液滴直径。     

微小燃烧器燃烧特性研究

微燃烧器中燃料的可靠点火与稳定燃烧是实现微动力系统正常工作的前提。本文进行了两种微小燃烧器的设计与燃烧实验。结果表明,通过在微小燃烧器内添加钢丝网,使两种小型燃烧器均获得了较宽的可燃范围。通过对微小燃烧器流场的数值分析,发现在微小尺度燃烧中,流场的均匀性对燃烧温度有重要的作用;在微小空间内添加钢丝网能够改善流场,拓展可燃范围。另外,钢丝网在高温下也能起到值班火焰的作用,对火焰稳定起到积极作用。     

液体火箭有机凝胶喷雾液滴蒸发模型及仿真研究

凝胶推进剂虽然兼具有液体推进剂流量可控和固体推进剂长期可储存等优点, 但凝胶喷雾液滴蒸发燃烧问题却一直困扰着凝胶推进剂研制及燃烧室设计工作, 阻碍了凝胶推进剂实际工程应用.设计实现了凝胶单液滴蒸发燃烧实验系统, 通过某型有机凝胶偏二甲肼(UDMH)单液滴在四氧化二氮蒸气中的蒸发燃烧实验现象, 进一步深入分析了凝胶液滴蒸发燃烧机理.根据实验中凝胶单液滴在不同阶段的蒸发特性, 建立了有机凝胶喷雾液滴在胶凝剂膜形成、膨胀、破裂三个不同蒸发阶段的多组分蒸发模型, 采用初步选定的模型参数及物性参数对凝胶单液滴在高温气体环境中的蒸发全过程进行了仿真计算, 并与常规液体液滴的仿真结果进行了对比分析.结果表明,凝胶喷雾液滴表面胶凝剂含量在蒸发初期增加比较缓慢, 但在某临界时刻后的极短时间内迅速升高至形成胶凝剂膜的质量分数95%, 导致表面质量流率迅速下降至0,表面温度则快速上升至UDMH推进剂沸点.胶凝剂膜形成后, 液滴半径及表面UDMH蒸气质量分数出现了实验现象中凝胶液滴反复膨胀-破裂的震荡现象, 液滴表面温度维持在略高于沸点的某温度范围内,凝胶液滴内部的沸腾蒸发明显强于液体液滴表面稳态蒸发流率, 使得凝胶喷雾液滴生存时间小于常规液体液滴.     

水平管外降膜蒸发的熵产分析

从热力学第一、第二定律的角度出发,结合水平管外降膜蒸发的特点,推导出了降膜蒸发过程单位熵产数Ns的公式,并在所建立的管外液膜厚度模型的基础上进行了求解。结果表明:沸腾蒸发时的单位熵产数Ns要小于表面蒸发时的值;采用强化表面可以有效地降低单位熵产数Ns;单位熵产数Ns随液膜雷诺数Re的变化比较小。通过分析,降膜蒸发的单位熵产分析法对于最大限度地减少不可逆损失、提高能量利用率等方面具有指导意义。     

连续式蓄热燃烧系统的实验研究

针对火焰切换式蓄热燃烧系统的不足和自蓄热燃烧器存在的问题,本文提出新的连续式蓄热燃烧技术方案,采用蓄热燃烧专用切换阀技术,开发出新型连续式蓄热燃烧系统。实验结果表明,该系统中单个燃烧器可以实现蓄热状态下的连续燃烧,炉内温度波动幅度变小,彻底改变了原自蓄热燃烧器存在的气流"短路"现象。     

煤粉低尘燃烧器热态试验研究

以液排渣旋风燃烧技术为基础的煤粉低尘燃烧器可在燃烧过程实现捕渣,为工业加热提供含尘浓度低的高温火焰,是工业加热过程实现以煤代油的先进燃烧技术。本论文介绍了新型煤粉低尘燃烧器的热态燃烧试验研究结果,该燃烧器采用端面旋流进风,煤粉和一次风在旋转气流外层送入,分级燃烧等技术。热态试验研究表明,采用上述技术的煤粉低尘燃烧器具有燃烧完全,捕渣率高,NOx排放浓度低等特点。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.