充液率对小型重力热管传热特性影响实验研究

开展了矩形槽道铝-乙醇小型重力热管的传热特性的实验研究,分析讨论了充液率对壁面温度分布、气液两相分布、热阻等热管传热性能的影响。研究表明,充液率对高热负荷工况的两相流动状态和传热特性有显著影响。两相脉动是高热负荷工况小型重力热管特有的两相流动现象.低充液率时,液塞易被气流冲破形成环状流,壁面温度几乎无波动。中等充液率时,在蒸汽和液塞的交替冲刷作用下,热管各段壁面温度均表现出脉动特性。高充液率时,液塞脉动速度的减小削弱了液塞对壁面的冲刷作用,壁面温度未出现明显波动.并且,中等充液率工况下气液两相的快速脉动增强了热管的传热性能,使得均温性和传热极限均优于低充液率和高充液率的情况.     

采用微通道换热器的分离式热管空调性能的试验研究

设计了基于微通道换热器的分离式热管空调系统,针对充液率、室内外温差以及冷凝器布置方式对空调性能的影响进行了试验研究。结果表明:高充液率和低充液率均会使分离式热管空调换热性能降低,系统最佳充液率为110%左右;室内外温差对分离式热管空调性能的影响显著,传热量随着温差的增大而增大,分离式热管空调传热量在20℃温差时比8℃温差时增加了348%;微通道冷凝器垂直布置时比平行布置时空调系统的充注量小,制冷量大。     

燕尾槽微小型热管的实验研究

本文对具有燕尾形(开式三角形)轴向槽道的微小型铜—水平板热管的传热性能,以及热管的倾角、充液率和槽道结构对其性能的影响进行了实验研究。结果表明,重力对热管性能的提高有辅助作用;热管的最佳充液率为1.2左右;燕尾形槽道结构较矩形槽平板热管性能更优越。     

纳米流体对脉动热管最佳充液率的影响

本文通过实验着重研究了一脉动热管在不同充液率下充入体积分数为0.05%、粒径为80 nm的柱状Al₂O₃纳米流体后传热性能的变化情况。结果表明:1)该纳米流体可以明显强化本实验中的脉动热管传热性能,但随着输入功率的增加,强化作用减弱;2)在充入该纳米流体后,脉动热管的最佳充液率由40%降为30%;3)充液率影响纳米流体的强化作用,总的来说充液率越高纳米流体的强化作用越弱。     

角管脉动热管的结构和尺度效应研究

根据角管毛细管中液体的分布以及汽液同向流动的特点,计算分析了正三角形和等腰直角三角形两种截面脉动热管中几种因素对热管传热性能的影响.计算结果表明,在充液率为 30% 时,两种角管脉动热管的热阻均在 0.1℃/W 以下;在相同加热功率和充液率时,等腰直角三角形截面脉动热管的传热性能优于正三角形截面的;截面形状相同时,水力直径较大的热管热阻值低于水力直径较小的热管;热管热阻值随接触角增大而减小.     

脉动热管的结构改进及其传热特性的实验研究

通过观察脉动热管的运行过程,并分析其存在的缺点,提出对脉动热管的结构进行改进,合理匹配各通道内的 流动阻力,实现工质在热管里的稳定单向流动,以改善加热段的供液情况,提高脉动热管传热性能。并对充灌率、倾角和 通道大小对改进型脉动热管的传热性能的影响进行了实验研究。     

脉动热管实验研究

建立了铜管脉动热管实验台,进行了实验研究.分析了在水冷的条件下,充液率、工质、倾斜角等因素对脉动热管传热性能的影响,结果发现,热阻随着充液率的增加而增大;选用蒸馏水、无水乙醇以及丙酮为工质时,在相同条件下,丙酮热阻最低;不同倾斜角的实验中垂直底加热时脉动热管热阻最低.     

低弯头数液氢温区脉动热管的实验研究

为了研究液氢温区脉动热管在冷却Mg B2超导磁体方面的可行性,利用浙江大学制冷与低温研究所现有的实验平台,进一步开展了液氢温区脉动热管的实验研究。在低弯头数(N=2)下,充液率55.8%的脉动热管在加热功率0.1W时可以启动;随着加热功率增大,经历了启动、脉动、极限三个阶段,启动阶段脉动热管传热温差波动很大、传热性能差,而脉动阶段脉动热管传热温差很小、传热性能好。在加热功率0.6W、充液率27.8%时,脉动热管具有最大的传热系数68k W/(m·K),此时蒸发段和冷凝段的温差为0.29K。     

板式脉动热管的实验研究

本文搭建了板式脉动热管的实验台并进行了实验研究。在电加热循环水冷却的情况下研究了小型板式脉动热管的启动和运行特性,以及脉动热管的倾斜角度、充液率、工质等因素对板式脉动热管换热状况的影响。实验结果表明,当热管启动运行时,热端温度降低冷端温度升高,热阻减少。不同充液率和倾斜角存在着不同的临界启动功率。管内真空度对启动运行有一定的影响。在本实验条件下,热管在垂直加热、充液率为30%、工质采用丙酮时传热效果最好。     

平板热管内气液两相流动与传热的可视化实验研究

本文基于高速摄像仪设计搭建了平板热管气液两相流动与传热的可视化平台,开展平板热管受限空间内气液两相工质运行状态和相变传热行为的可视化观测。研究结果表明,平板热管存在突然启动和渐进式启动两种启动方式,在高充液率情况发生突然启动,而在低充液率情况下发生渐进式启动。在准稳定运行阶段,蒸发面先处于能量积累状态,随后热量伴随着核态沸腾快速释放到冷凝面,热管蒸发段和冷凝段壁面温度表现出周期性的温度脉动变化。在热量积累过程中平板热管蒸发段与冷凝端之间的传热性能弱,在核态过程中蒸发段与冷凝端之间的传热性能强。     

An investigation on the static electrification of dimethyl ether

Static electrification characteristics of dimethyl ether (DME) were studied considering accidents during unloading (discharging) operations. Producing mist flow, static electrification by the mist was studied as a first step. Influences of flow velocity on the charge generation, produced potential, charge generation ratio, electrostatic energy, etc. were investigated experimentally. Although the produced charge is not too big, it will be requested to pay full attention during the handling process, considering the igniting characteristics of DME.     

±100 kV三电极场畸变气体火花开关

设计了一种用于直线变压器驱动源的三电极场畸变气体火花开关。开关采用SF6气体绝缘,开关尺寸和电感较小,实测开关电感约为67 nH。在工作电压80 kV、工作系数为70%时,开关触发时延为40.0 ns,抖动约2.8 ns。对比研究了钨铜合金和黄铜两种电极材料对开关静态和触发击穿特性的影响,研究结果表明:铜钨合金电极开关的自击穿电压分散性、触发时延及抖动、自放电概率和电极表面烧蚀均小于黄铜电极,更适宜作为三电极场畸变开关的电极材料。     

Frequency transformation of optical vortices upon nondegenerate multiwave interaction in dye solutions

A method for inverting the topological charge of singular light beams with their simultaneous frequency transformation under multiwave interaction in media with resonant and thermal nonlinearities is proposed. Frequency-nondegenerate four-wave and six-wave interactions of optical vortices are experimentally implemented using an ethanol solution of a polymethine dye 3274U as a nonlinear medium.     

Effect of the optical characteristics of semiconductor resonator structures on the amplitudes of their thermal radiation lines

We investigated, both theoretically and experimentally, the dependence of the intensity of spectral lines of thermal radiation from plane-parallel semiconductor resonator structures on their optical parameters (volume absorption and coefficients of reflection from surfaces). The investigations were performed in the spectral region of absorption by free charge carriers (λ = 3–17 μm). It is shown for such structures that the amplitudes of thermal radiation lines depend non-monotonically on the transmission factor. We determined the optical parameter values for a resonator structure that are optimal when forming comb radiation spectrum. The conditions are found under which the intensity of lines of thermal radiation from a semiconductor plane-parallel layer approaches that of thermal radiation from a blackbody.     

Light-induced absorption in reduced congruent and near-stoichiometric Er:LiNbO3 crystals

Light-induced absorption (LIA) in thermally reduced congruent and near-stoichiometric Er:LiNbO₃ crystals, which have different cuts of crystal (X- and Y-cut) and different doping levels of Er³⁺ (0.2, 0.4, 0.6 and 1.0 mol %), has been studied within continuous-wave light intensity by using polarized 632.8 nm beam as probe light and polarized 488 nm beam as pump light. Effects of thermal reduction condition, pump intensity, Li/Nb ratio and Er-doping level on the LIA are summarized and discussed. Studies on spectral characteristics of both linear absorption and light-induced absorption show that photo-ionization of bipolarons into small polarons plays a predominant role in the LIA process. The role of the Er³⁺ ion in the LIA is investigated by studying the doping level and the thermal reduction effects on the absorption and emission properties of Er³⁺. The results show the possibility that the Er³⁺ ion directly participates in the light-induced charge transport is small. It affects the LIA only via the bypassing part of pump intensity to excite near-infrared emissions of Er³⁺. The thermaleffect on the LIA is demonstrated. A two-center model with inclusion of the thermal contribution can qualitatively explain two major LIA characteristics that include the appearance of a slow stage in the LIA procedure and the unsaturation behavior of the LIA coefficient in high pump intensity regime. In addition, the pump depletion effect on the LIA characteristics is discussed. The possibility of pump beam fanning arising from light-induced scattering is ruled out experimentally. PACS 42.70.Hj; 42.70.Ln; 42.70.Mp; 42.65.Hw; 81.05.-t     

Charge-drift and dispersion in deep inelastic collisions in an equilibrium model

First and second moments of the charge distribution for the reaction⁸⁶K +¹⁶⁶Er have been calculated assuming a thermal equilibrium model. The moments are calculated microscopically on the basis of a realistic two-center shell model as a function of distance as well as of excitation energy. The experimentally observed constancy of the first moments is reproduced.     

Energy dispersion of localized states in light-sensitive nanocrystals

The kinetics of the formation and thermal destruction of color centers in CuCl and AgCl nanocrystals (NCs) distributed in a glass matrix is described on the basis of the band model of an NC with colloidal color centers and with hole traps of one species. The possibility of experimentally determining the relative depth distribution of hole states in light-sensitive NCs in glass is demonstrated. The observed energy dispersion of localized hole states and its variation in NCs are associated, in accordance with Dexter’s idea, with large-scale thermal fluctuations of the crystal field. The presence of an excess charge on a colloidal particle and its influence on localized hole states are presumed.     

Fe：LiNbO3晶体光折变全息热固定动力学特性分析

以Fe:uNbO3晶体为例,考虑了电子载流子热激发(强烈地依靠于温度),通过对以扩散和光伏特效应为主导输运机制的带输运方程和耦合波方程进行数值求解,分析了热固定过程初始光强入射比和固定温度对光栅空间电荷场的影响,指出记录固定过程中内电场极值的出现来源于质子电场对施主光栅电场的部分补偿,质子光栅电荷场可以导致晶体中记录光束之间能量耦合方向的变化,得出了理论上的加热固定时间。     

Synchronization of oscillations in a backward-wave tube: Theory and experiment

Synchronization of oscillations in an electron-wave system with a backward electromagnetic wave is studied theoretically and experimentally. The characteristics of nonautonomous oscillations in the backwardwave tube are analyzed with allowance for the space charge and physical processes accompanying the transition of the distributed autonomous system to the synchronization regime. Theoretical results are compared with experimental data.     

Stabilized parametric cooper-pair pumping in a linear array of coupled Josephson junctions

We present an experimentally realizable stabilized charge pumping scheme in a linear array of Cooper-pair boxes. The system design intrinsically protects the pumping mechanism from severe errors, especially current reversal and spontaneous charge excitation. The quantum Zeno effect is implemented to further diminish pumping errors. The characteristics of this scheme are considered from the perspective of improving the current standard. Such an improvement bears relevance to the closure of the so-called measurement triangle (see [D. Averin, Nature (London) 434, 285 (2005)).