BD-PND中子气泡探测器性能的检验

依据国家有关标准和参照ISO／DIS 21909标准的规定和要求,对放置近2年的BD-PND（Bubble Detector Personal Neutron Dosimeter）中子气泡探测器的均匀性、线性、中子个人剂量当量的响应、重复性和角响应等主要技术性能进行了检验。结果表明,基本符合标准规定的要求。采用修正的响应值可以用于低水平的个人中子剂量测量。因这些探测器的寿命将近终点,应谨慎使用。     

两种介入治疗(CA与PTCA)中患者所受剂量调查

大多数介入放射学着眼于研究治疗中的新手术、新设备以及临床经验,然而如何实现介入程序中的辐射防护正当化与最优化也是介入放射学所面临的重要课题。本课题采用剂量面积乘积仪,对在北京宣武医院就诊的51例经皮穿刺腔内冠状动脉成形术(PTCA)及冠状动脉血管造影术(CA)病人所受的辐射剂量进行了调查。结果表明,他们的平均剂量DAP(剂量-面积乘积)分别为22.77 Gy.cm2(CA,33例)和62.96 Gy.cm2(PTCA,18例)。本文同时对相关参数与剂量的关系进行了分析,并与其它研究的剂量参考水平(DRL)值进行了比较。     

倾斜下朝向加热表面汽泡行为可视化实验研究

以AP1000反应堆堆芯熔融物堆内滞留(IVR)策略为研究背景,采用去离子水为工质,在大气压下针对倾斜矩形结构开展下朝向加热表面汽泡行为的可视化实验研究。加热表面倾角从0°变化到30°,矩形窄缝尺寸从3 mm变化到8 mm。可视化观察到下朝向加热表面的汽泡滑移和汽泡变形现象,认为实验本体结构和下朝向加热表面布置是导致汽泡滑移和变形的诱因。通过对临界热流密度触发前后汽-液两相波动现象的可视化分析,认为汽-液波动界面的脱离是触发临界热流密度的主要原因。     

The effect of wetting properties on bubble dynamics and fuel distribution in the flow field of direct methanol fuel cells

We investigate CO₂ bubble dynamics on the anode side of a direct methanol fuel cell (DMFC). In contrast to previous studies, we analyse the effect of both channel wall and diffusion layer wettability by observing two-phase flow from the side at different mean velocities of the fuel supply. Hydrophobic and hydrophilic flow channel surfaces are compared experimentally. The hydrophilic flow channel leads to a minimum pressure drop along the channel. Bubbles show virtually no pinning and consequently travel at approximately the mean fuel velocity inside the channel. In contrast to this, we observe bubble pinning in the hydrophobic flow channels. The critical fuel velocities necessary for detachment of the bubbles mainly depends on bubble length. We identify and describe a new bubble bypass configuration where fuel bypass channels are solely generated in a favourable position underneath a blocking bubble along the diffusion layer. This enforces fuel to bypass the CO₂ bubble at a large relative velocity close to the diffusion layer, thus enhancing mass transfer. Our experimental findings are in excellent agreement with a CFD/analytical model. This model allows for quantitative prediction of average bypass flow velocity.     

Hydrodynamik in Blasensäulen – Messung von relativem Gasgehalt und Blasengröße

In bubble column reactors mass transfer kinetics are determined by local hydrodynamic processes (bubble formation, velocity, coalescence, break‐up, etc.). For a better understanding of the influence of pressure and particle load on these processes, a measurement system for detection of local bubble size distributions in opaque bubbly flows is needed. Therefore, in this work an optical needle probe was applied in a bubbly flow. In a first step, the needle probe was validated by means of single‐bubble measurements. The measurement technique shows high potential for application in more complex and opaque systems.     

The effect of multi-orifice plate configuration on bubble detachment volume

The multi-orifice plate gas sparger, mainly composed of a multi-orifice plate and a gas chamber, is one of the most common sparger facilities. The aeration performance of multi-orifice plate has a close relation with the multi-orifice plate configuration. In addition, the weeping phenomenon has a considerable influence on the gas chamber condition which affects the bubble detachment volume directly. This paper conducts a set of visual experiments to study the influence of multi-orifice configuration and gas chamber condition on the aeration performance of gas sparger. For multi-orifice plate, an improved theoretical model is proposed which considers the wave effect of the previous bubbles generated from adjacent orifices and the variance of the number of active bubbling orifice. A parameter is proposed to evaluate the aeration performance in order to overcome the difficulty caused by the randomness of bubble formation process. The experimental results suggest that the gas chamber filled with water is in favor of large bubble formation. The influence of the pitch of orifice on aeration performance can only be observed in high-restricted case. According to the theoretical model and experimental results, the influences of gas flow rate and the number of open orifices on the aeration performance are analyzed and a design criterion for the number of open orifice is proposed.     

Effects of photo-generated gas bubbles on the performance of tandem photoelectrochemical reactors for hydrogen production

Presence of gas bubbles in the vicinity of semiconductor electrodes interferes with their active surface areas and introduces inert voids in the electrolyte hindering its ionic conductivity. Furthermore, gas bubbles obstruct the radiation path through scattering. The aim of this work is to study the characteristic hydrogen- and oxygen-gas bubble behavior and their effects on photoelectrochemical reactor performance. Findings of gas bubble formation, electrode coverage and curtain profiles based on macroscopic bubble graphical images are reported. Effects of increased convective forces are also observed. Further, the scattering of incident light implemented through simulations based on Mie scattering theory is reported. Results show that hydrogen gas bubbles are more extensive in coverage due to formation of a froth while oxygen bubbles coalesce and rise easily. The growth of the bubble cover increases ohmic resistance reducing the current magnitude. Even at a modest current density of 10 mA/cm², the curtain thickness may rise to 2 mm or 3 mm for oxygen and hydrogen, respectively. Light scattering increases with increasing bubble size and is more pronounced for shorter wavelengths. It is also found that presence of multiple bubbles reduces light intensity by up to 2% and highest when the bubble radius is 150 μm. Increase in both photoelectrode and electrolyte resistances as well as radiation losses due to presence of bubbles hence undermine the performance of photoelectrochemical reactors.     

精炼时利用小气泡搅拌去除钢液中的氢和夹杂物

通过理论计算研究和分析了钢液气泡直径、吹气量和吹气时间对精炼时去氢和夹杂的影响。氩气经透气砖进入钢液后会形成大量的气泡,小气泡在钢液中能有效地增大脱气面积,有利于减小钢液中的氢含量。夹杂物与气泡的粘附上浮是钢液中去除夹杂物的一种有效方式,气泡越小、夹杂物越大,夹杂物就越容易去除。在钢包精炼过程中,应使用小气泡来达到较好的去氢和去夹杂效果,气泡的最优直径为1～3 mm。     

气固流化床中颗粒分离研究进展

综述了气固流化床有关颗粒分离的研究概况及最新进展。既包括实验研究，又给出模型比较。讨论了不同研究结果之间的差异及存在的不足。指出了在这一领域中应该进一步进行深入研究的课题。