小型外置式氦低温纯化器的换热器设计与优化

在整个氦制冷循环系统中,用来净化低温氦气中杂质的外置式纯化器起着不可或缺的作用。而在整个纯化器的设计中,换热器的设计显得极为重要。该设计选择套管换热器,首先确定套管换热器的内外管径以及壁厚;其次根据经验公式通过低温氦气的工况得出换热管的总换热系数,对换热器盘绕直径进行优化后确定换热器尺寸;然后通过对研制出的纯化器进行实验分析,验证换热器的性能符合设计要求。     

CFETR 25kW 4.5K氦制冷机RAMI初步分析

对25kW/4.5K氦制冷机进行了可靠性、可用性、可维修性和可监测性(RAMI)分析,建立了其可靠性框图,计算并评估了系统的可靠性和可用性。同时,通过故障、影响和危害分析指出了氦制冷机的故障模式,并提出了缓解和维护措施。     

氦液化器内纯化器实验与模拟研究

利用内纯化器实验平台,对氦氮混合气体及氦氧混合气体进行了纯化实验,根据实验结果计算出换热器UA随着压力及气体组分的变化,分析冷凝液膜的变化及对内纯化器换热性能的影响;建立全尺寸冷凝换热器模型,增加氦气-空气混合气体,进行模拟计算,得到管内外流体温度场分布,计算UA值的变化并与实验结果对比,进一步计算了管外流体Nu数、Pr数及Re数的变化,并和利用传热科伯因子法计算得到的Nu数相比较,发现在内纯化器冷凝换热器设计中存在的问题及改进的方向。     

内纯化器在氦低温系统中的应用

近年来,随着国家重大科技基础设施发展的需要,作为其关键设备的低温氦制冷系统取得了重大发展,同时也促进了内纯化器发展。文中简要介绍了内纯化器国内外发展的现状、内纯化器纯化的过程以及内纯化器研制的意义。     

EAST 2kW/4K氦制冷机检漏及真空系统运行情况

介绍EAST超导托卡马克2kW/4K氦制冷机的检漏方法及检漏过程,制冷机的真空系统及运行情况,指出关于大型氦低温系统检漏要注意的一些问题。     

基于可用能和熵产分析500 W/4.5 K氦制冷机优化

利用流程模拟软件对500 W/4.5 K氦制冷机建立静态模型,建立制冷循环的可用能效率以及系统熵产的分析公式.选取透平路分流系数、透平路中间压力、透平路进口温度和压机出口压力关键参数为研究对象,采取氦制冷机的可用能效率分析和系统熵产分析相结合的研究方法,对氦制冷流程进行优化分析.优化后的500 W/4.5 K氦制冷机的...     

CSNS/RCS次级准直器吸收体的冷却设计

作为CSNS/RCS横向束流准直系统的关键部件,次级准直器用于吸收经主准直器散射后不在预定轨道的束晕粒子,其工作原理决定了该设备要求满足强辐射环境下的稳定性、超高真空及高定位精度等要求。基于主准直器的设计及研制经验,对次级准直器结构方案及控制系统进行详细设计。针对关键部件吸收体,结合辐射防护分析结果,考虑水冷降温的方式,设计了控制程序,通过有限元分析软件ANSYS对其进行瞬态热分析,保证吸收体设计的可行性。     

空间遥感器高体份SiC/Al复合材料反射镜组件设计

为消除反射镜与支撑结构材料线胀系数差异产生的热变形对反射镜面形精度、系统成像质量的影响, 采用高体份SiC/Al复合材料作为新型反射镜组件的材料。首先, 通过合理的结构设计及有限元分析比较, 确定了Ф600 mm口径反射镜结构参数, 然后, 对反射镜组件进行了静力学和动力学分析, 在1 g重力载荷作用下, 反射镜X、Y、Z方向去除刚体位移后的镜面变形RMS值分别为12.6, 12.7, 12.6 nm, 达到了λ/50(λ=632.8 nm)。最后, 为了验证高体份SiC/Al复合材料反射镜组件的结构性能及检验结构在振动条件下的抗干扰能力, 对反射镜组件进行了力学试验, 反射镜组件的一阶谐振频率为556.6 Hz。力学试验前后, 反射镜镜面面形误差RMS分别为0.021λ、0.025λ, 没有明显变化。实验结果表明:高体份SiC/Al复合材料反射镜达到了与SiC材料反射镜相同的设计指标要求, 能够满足空间应用。     

超流氦制冷系统2K冷却级热力分析

通过对节流阀阀前J-T换热器的效率以及2 K冷却级的制冷量等参量与节流阀前温度、压力以及J-T换热器冷、热端温差等关系的分析表明,考虑比热变化时J-T换热器的效率均低于不考虑比热变化时的J-T换热器的效率,且发现在降低换热器入口温度来提高单位质量氦气的2 K制冷量时,J-T换热器的热效率将降低。分析结果表明为避免系统变工况运行时换热器运行出现负温差,建议J-T换热器应该以限定冷端温差进行设计。     

氦原子自旋-其它轨道相互作用精细结构参数的理论计算

以多电子原子精细结构哈密顿的球张量形式和氦原子非相对论性能级结构理论为基础,借助不可约张量理论,建立了计算氦原子自旋-其它轨道相互作用精细结构参数的一种解析理论形式.完成了所有的角向积分和自旋求和计算,自旋-其它轨道相互作用精细结构参数最终用若干个径向积分来表示.以氦原子(1s2p)3P态为例,借用类氢形式的径向函数对这些径向积分进行了近似计算.计算结果表明:在氦原子的精细结构中,自旋-其它轨道相互作用与纯自旋-轨道相互作用的作用效果相反;在总自旋-轨道相互作用精细结构参数中,自旋-其它轨道相互作用起决定性作用,它决定着精细结构分裂的顺序.     

Differential equation for the ground-state density of a model spin-compensated atom in an external potential

The study of Gál and March (2009) [1] is utilized to derive a third-order differential equation for the ground-state electron density of two-electron model atoms having inverse-square repulsion, but arbitrary external potential. The result offers hope of progress on He-like atomic ions.     

Fast relaxation of the metastable helium state 2S0 in collisions with molecules and collisional lasing on the He (2P1-2S0) transition

In the present study, the laser absorption method was used to measure the rates of quenching of the metastable state He(2¹S₀), the lower laser level in the self-terminating helium laser, with H₂O, NH₃, N₂O, and CO₂ molecules. For the above molecules, the quenching rate constants were found to equal (1.2 ± 0.3)10^− 9, (0.8 ± 0.2)10^− 9, (1.9 ± 0.2)10^− 9 and (2.2 ± 0.4)10^− 9 cm³ s^− 1. Under excitation with long (up to 750 ns) open discharge generated electron beam pulses, lasing on the transition He (2¹P₁⁰-2¹S₀) was examined. In the mixtures He-H₂O and He-NH₃, lasing durations almost equal to the pump-pulse duration were obtained. In the mixtures of He with CO₂ and N₂O, no lasing prolonged in comparison with pure helium was found. The data obtained were explained considering two quenching mechanisms for the state He(2¹S₀): in collisions with molecules and in collisions with plasma electrons having low energies due to fast relaxation of the vibrational states of H₂O and NH₃ molecules.     

ORG500W/4.5K制冷机的改造流程设计计算及分析

介绍了带LN2预冷的二级膨胀循环的流程计算方法,并提出了优化计算的思路和计算机程序实现的方法;最后就换热器热端温差对制冷机效率的影响进行了讨论     

Ultrasound-assisted adsorption/desorption for the enrichment and purification of flavonoids from baobab (Adansonia digitata) fruit pulp

This work described the purification and enrichment of flavonoids from baobab (Adansonia digitata) fruit pulp (BFP) by ultrasound-assisted adsorption/desorption procedure using macroporous resins. Four resins were tested and HPD-500 polar resin exhibited the best adsorption/desorption properties. Based on preliminary experiments and literature reports, the effects of various ultrasonic conditions including high power short time (HPST, 540 W for 5 min), medium power medium time (MPMT, 270 W for 15 min) and low power long time (LPLT, 45 W for 30 min) as well as different temperatures (T = 25–45 °C) on the adsorption of Total Flavonoids Content (TFC) were investigated in comparison with orbital shaking/no sonication (NS). Also, the effect of ultrasound on the desorption capacity and recovery of TFC was determined at different concentrations of ethanol (30–100%). Remarkably, ultrasonic treatment significantly increased the adsorption/desorption capacity and recovery and shortened the equilibrium time. The pseudo-second-order kinetic and Freundlich isotherm models better delineated the adsorption process under ultrasound. Moreover, the adsorption process was both spontaneous and thermodynamically favourable with physical adsorption and multilinear intraparticle diffusion being the predominant mechanisms of the whole process. HPST treatment at 25 °C with 80% ethanol as the desorption solvent most noticeably enhanced the adsorption/desorption of flavonoids and contributed to the highest recovery of TFC, Total Phenolic Content (TPC), and antioxidant capacity in addition to a 5–8-fold reduction in total sugar and acid contents when compared with NS treatment. Moreover, HPLC analysis revealed that the content of nine out of thirteen phenolic compounds from the HPST treatment was the highest, and the individual flavonoids content increased by 2–3-fold compared with the other treatments. Our analyses suggested that ultrasound can be employed as a practical approach to intensify the adsorption and desorption of functional compounds in BFP.     

A modified pitchfork bifurcation as a model of the TI–TII transition in liquid helium counterflow with external noise

An amended pitchfork bifurcation is introduced to model recent experiments by Griswold and Tough on superfluid turbulence in liquid helium counterflow subject to strong external noise. We adopt the generalized white noise limit of Blankenship and Papanicolaou to take a short-correlation-time limit of the nonlinear noise which enters into the model, and we implement this limit by means of the wideband perturbation expansion. Novel boundary conditions are applied to the resultant diffusion process in order to obtain behavior in qualitative agreement with the observations at low vortex line density. We are able to account for the sharp peak in probability observed experimentally at a small positive line density. The drift and diffusion of our diffusion process may be estimated experimentally; we describe how to do this.     

Total Internal Reflection Fluorescence Spectroscopy for Investigating the Adsorption of a Porphyrin at the Glass/Water Interface in the Presence of a Cationic Surfactant Below the Critical Micelle Concentration

Total internal reflection fluorescence (TIRF) spectroscopy was used to investigate the adsorption behavior of meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS) at the glass/water interface in the presence of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) far below the critical micelle concentration. The adsorption model of TPPS at the glass/water interface in the presence of low concentration of CTAB was proposed, which was different from the adsorption of TPPS in the presence of micelles of CTAB at the glass/water interface. TPPS and CTAB did not form stable complex at the interface in dilute system. The interfacial species of TPPS were analyzed by comparing the spectra of TPPS at the glass/water interface and in the aqueous phase. The influences of the TPPS concentration, the CTAB concentration, and the pH values on the interfacial fluorescence spectra and intensities were studied. It was demonstrated that electrostatic interaction and hydrophobicity performed an important role on the adsorption of TPPS in the presence of CTAB. The different effects of TPPS concentration on the adsorption behaviour of TPPS at different pH were observed for the first time. It was found that the adsorption isotherms of TPPS at glass/water interface could fit Freundlich equation at pH 7.1.