大面积热阴极系统设计及初步实验结果

建立了能满足大面积热阴极系统需要的2MeV热阴极实验平台, 并配合研制了直径为100mm的B型储备式热阴极. 在二极管电压为1.8MV、脉宽90ns(FWHM)、阴极工作温度为1350℃情况下, 利用法拉第筒获得了1000A的发射电流, 发射电流密度约12A/cm². 实验结果表明, 利用大面极热阴极获得高亮度强流电子束在工程上是可以实现的. 实验结果也表明, 阴极发射能力强烈依靠于二极管真空和阴极工作温度.     

复叠式低温保存箱系统设计关键问题分析

以R404A/R23为制冷剂,利用二元单级复叠制冷循环,开发出-86℃大容量低温保存箱。文中对蒸发器优化布置、冷凝蒸发器中间温度确定、毛细管设计以及如何保证设备安全运行等关键问题进行了分析。     

工程车用空调器的设计及主要生产工艺

本特种工程车用空调器采用蒸气压缩制冷原理,即利用液态制冷剂吸热汽化产生制冷效应,利用车上的发动机作为驱动源,通过皮带传动带动压缩机工作,使制冷剂在系统内产生循环,通过换热器与空气进行热交换,从而实现车室的降温要求。制冷剂采用新型环保制冷剂R134 a,整机结构紧凑、性能可靠、换热效率高。     

Comprehensive performance of a ball-milled La0.5Pr0.5Fe11.4Si1.6B0.2Hy/Al magnetocaloric composite

Due to the hydrogen embrittlement effect, La(Fe,Si)₁₃-based hydrides can only exist in powder form, which limits their practical application. In this work, ductile and thermally conductive Al metal was homogeneously mixed with La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2 using the ball milling method. Then hydrogenation and compactness shaping of the magnetocaloric composites were performed in one step via a sintering process under high hydrogen pressure. As the Al content reached 9 wt.%, the La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2H_y/Al composite showed the mechanical behavior of a ductile material with a yield strength of ~44 MPa and an ultimate strength of 269 MPa accompanied by a pronounced improvement in thermal conductivity. Due to the ease of formation of Fe-Al-Si phases and the several micron and submicron sizes of the composite particles caused by ball milling process, the magnetic entropy change of the composites was substantially reduced to ~1.2 J/kg· K-1.5 J/kg· K at 0 T-1.5 T.     

星载多路短波红外探测器温控系统设计

主要针对星载多路短波红外探测器的温度要求设计了高精度在轨温度控制系统。首先,在对工作温度控制需求进行分析的基础上,提出了该系统短波红外探测器的温度高稳定性要求;其次设计了高稳定性温度采集电路、低噪声热控驱动电路,并且在FPGA芯片上基于开关控制算法,产生了脉宽调制信号;然后利用该脉宽调制信号控制热电制冷器的驱动电流,实现了在资源有限的条件下,温度控制高稳定度的要求。最终性能测试的结果表明,温控的精度可以达到±0.1°的高稳定度要求,满足该多路短波红外探测系统星载工作温度要求。     

Room-Temperature Symmetric Giant Positive and Negative Electrocaloric Effect in PbMg0.5W0.5O3 Antiferroelectric Ceramic

As an emerging solid-state refrigeration technology with zero-emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects (ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg_0.5W_0.5O₃, containing non-equivalent B-site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first-order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g⁻¹, more than four times that of BaTiO₃. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg⁻¹ K⁻¹) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg⁻¹ K⁻¹) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg_0.5W_0.5O₃ a superior electrocaloric material far beyond traditional PbZrO₃-based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications.     

钼阳极二极管测试大尺寸阴极发射性能的应用研究

针对大尺寸、高功率阴极在工程应用上的发射性能检测不准确问题,我们设计了不同钼阳极二极管结构并进行仿真计算,选择不同直径和深径比的阴极进行实验。仿真计算结果显示球面、栅网阳极二极管的结构可较好地表征了阴极发射电流,明显优于平面阳极二极管结构。应用研究结果与仿真结果一致,考虑工程应用成本,球面阳极二极管结构利于筛选出工程应用阴极。     

一种采用半导体致冷的集成大功率LED

介绍了一种采用半导体致冷技术散热的集成大功率发光二极管(LED),这种利用珀尔贴效应设计的大功率LED散热封装结构,不但可以从根本上解决大功率集成LED器件的散热问题,还可以使LED器件在高温、震荡等恶劣环境中正常工作.这样,既可拓宽LED的运用领域,又能有效延长大功率LED的寿命.采用该封装技术封装的白光LED,发光稳定,光衰小,寿命长.     

显微光子计数成像系统的噪声抑制及定量测量标准的确立

显微光子计数成像系统是极其灵敏的弱光探测成像系统,为使其应用进一步深入微观领域,噪声问题是首先要解决的难题。通过噪声来源分析,光路、机械结构的合理设计,使噪声降低到光子计数成像系统的探测灵敏域之下;并在噪声极低的条件下,进行了一种同位素微弱光源的稳定性、均匀性的研究,发现这种微弱光源性能稳定、发光均匀,可以作为定量测量的标准,为以后的微弱发光实验进行定量分析;光子计数成像系统的合理噪声抑制以及定量测量标准的确立,将在微光探测方面产生重要的影响。     

Capillary Electrophoresis Coupled On-Line with Nitrogen-Selective Thermionic Detection Using an Eluent-Jet Interface

The on-line coupling of capillary electrophoresis (CE) with a thermionic detector (TID) originally developed for gas chromatography (GC) is reported for the first time. An eluent-jet interface previously used to combine micro-liquid chromatography and mass spectrometry can now be used to couple CE and TID. Preliminary results demonstrate the possibility of performing direct nitrogen-selective detection, even for less volatile compounds. Detection limits of 4–12 pg N/s were obtained for the four tested compounds piperidine, dimethylformamide, tetra-n-butylammonium hydroxide, and nicotinic acid. Optimization of both the TID and the eluent-jet interface can be performed independently; optimum TID parameters agree rather closely with the detector specifications under GC conditions. The nitrogen-selective TID proved to be linear over more than three orders of magnitude with acceptable repeatability. The on-line coupling of CE and TID may well become an interesting approach for the rapid and direct analysis of ionic and high-molecular-mass N-containing compounds.