安全壳内PCS换热器气溶胶自然沉积特性研究

核电厂出现严重事故时,非能动安全壳冷却系统(PCS)的运行能够促进悬浮气溶胶的自然去除过程,减少可能释放到环境中的放射性物质。该文建立了PCS换热器单根传热管的传热与气溶胶沉积模型,研究了传热管壁面的气溶胶沉积规律。结果表明,重力沉降速率随传热管周向角度成正弦变化,扩散泳和热泳沉积速率沿传热管管程逐渐减小。在恒定热工水力条件下,气溶胶在换热器表面的总去除系数随粒径的增大先缓慢降低,然后显著增大。     

生物气溶胶在分子生物学方面的研究进展

主要介绍近年来生物气溶胶在分子生物学方面的研究进展。蛋白质气溶胶可以作为一种呼吸道疾病治疗药物和免疫源,因此如何释放蛋白质气溶胶并保持蛋白质活性是关键。基因治疗和基因免疫也是近年刚兴起的一个研究领域,质粒ＤＮＡ的气溶胶化技术和呼吸道吸入后的转染及表达研究,是呼吸道粘膜免疫和疾病治疗的重点。在生物气溶胶检测方面,近年也引进了多聚酶链反应技术,从而大大提高了检测的敏感性和空气传播的致病微生物的检测速度。     

真空冷冻干燥机内的水蒸气压力分布计算

试图从冻干过程中冻干室内水蒸气压力分布不均匀的角度,分析解释大型真空冷冻干燥机存在的不同部位物料干燥速率不均匀问题.通过建立描述搁板层间通道和搁板组间抽气通道内水蒸气流动的数学模型,计算得出流动通道内的水蒸气压力分布规律.定义了2个通道特征系数,反映出冻干机结构、工艺参数对水蒸气压力分布的影响作用.计算结果可以用于估算冻干机内不同部位物料的干燥速率,并可为确定冻干机关键结构工艺参数提供重要的理论参考依据.     

化学吸附式制冷系统传热传质的数值模拟和实验研究

运用多孔介质理论分析了化学吸附式制冷系统中的吸附床,按多孔介质的质量、动量和能量传递过程建立了吸附床内流动、传热和传质耦合求解的数学模型,并根据吸附剂在吸附床内多孔介质中的流动特性,采用比经典的Darcy模型更精确的多孔介质流动模型-Ergun模型。所建立的数学模型较之现有的吸附床传热传质数学模型能更全面、准确的描述吸附床的传热传质特性。将所建立的模型对化学吸附制冷样机进行了模拟计算,计算结果和测试结果吻合得较好。数学模型和计算结果有助于深入认识吸附床的传热传质特性,并可进一步用于吸附床和系统的优化设计。     

气溶胶粒子特性对激光衰减系数的影响

1.06 μm激光通常依赖经验数据或典型气溶胶模式计算大气消光系数,无法将理论计算与实际的气溶胶情况相结合,其精度无法满足激光武器的要求.本文通过在绥中地区多种天气下进行的1.06 μm激光大气衰减实验,验证了依据气溶胶大气模型数据计算得到的消光系数与真实数据存在较大误差,即典型气溶胶模式与绥中地区实际气溶胶情况不一致...     

C/SiC复合材料等温化学气相浸渗过程的数值模拟研究

根据C/SiC复合材料的结构以及等温化学气相浸渗法的工艺特点, 建立了ICVI过程中C纤维预制体结构变化的多尺度孔隙模型和C/SiC复合材料ICVI致密化过程的数学模型. 利用该模型对ICVI法制备C/SiC复合材料进行了数值计算和分析. 模拟结果与实验结果呈现出相同的规律并且两者之间误差较小, 表明本文所建立的模型可以很好地描述C/SiC复合材料的ICVI致密化过程. 利用该模型计算出C/SiC复合材料孔隙率的分布情况以及总体孔隙率在浸渗过程中的演化规律, 对ICVI工艺的优化具有一定的指导意义.     

平板焊接接头纵向残余应力修正估算公式

为研究不同焊接参数对平板焊接接头残余应力大小的影响规律, 采用ANSYS软件, 建立了大量焊接试件的三维热弹塑性有限元模型, 对其温度场和应力场进行了数值模拟. 根据数值模拟结果, 考虑不同焊接参数、焊道数以及板件热流分配系数的影响, 对拉应力区半宽的计算公式进行了修正. 在此基础上, 采用指数函数对纵向焊接残余应力进行了拟合, 得到了预测不同焊接接头纵向残余应力分布规律和大小的修正估算公式. 最后设计了多组焊接构件模型, 采用盲孔法实测了其残余应力大小和分布规律, 并与估算公式的计算结果进行了对比, 结果表明:两者吻合良好, 验证了该文修正残余应力估算公式的有效性.     

焊接气溶胶喷射速率模型研究

基于焊接电弧特性和发尘特性提出等效发尘面积概念,通过分析发尘量与焊接参数之间的关系,建立了电弧焊焊接气溶胶喷射速率的数学物理模型,并推导出数学表达式.用该式对不同焊接线能量时E5015焊条电弧焊气溶胶喷射速率进行计算,结果表明随着焊接线能量的增加焊接气溶胶的喷射速率也相应增大,且速率值与一般实测结果基本一致,说明本文提出的焊接气溶胶喷射速率模型是合理的.这对焊接气溶胶扩散的数值模拟,更有效地实现对焊接气溶胶的控制具有重要意义.     

硬岩中爆炸冲击波衰减规律的数值模拟

利用ANSYS/LS-DYNA有限元分析软件,建立了硬岩介质中装药爆炸的数学模型,对硬岩体中的爆炸冲击波的传播衰减规律进行了数值计算。数值计算模型计算得到的爆炸冲击波压力与经验公式计算的冲击波压力数据基本一致,验证了该模型的正确性。     

高温气冷堆蒸汽发生器中的石墨粉尘沉积

为了研究高温气冷堆内石墨粉尘沉积行为,通过构建氦气实验回路,设计蒸汽发生器封头及换热单元模拟件,研究氦气载带的石墨粉尘在高温气冷堆蒸汽发生器内特征结构处的沉积情况,分析不同流量和温度下蒸汽发生器底部和蒸汽发生器换热单元的石墨粉尘沉积量与沉积分布。结果表明:蒸汽发生器人孔处会有大量的石墨粉尘残留;蒸汽发生器换热单元下部沉积大于上部,经估算,单个换热单元内饱和沉积量约为222. 6 g。     

Assessment of environmental radon hazard using human respiratory tract models

Radon is a natural radioactive gas derived from geological materials. It has been estimated that about half of the total effective dose received by human beings from all sources of ionizing radiation is attributed to 222Rn and its short-lived progeny. In this paper, the use of human respiratory tract models to assess the health hazard from environmental radon is reviewed. A short history of dosimetric models for the human respiratory tract from the International Commission on Radiological Protection (ICRP) is first presented. The most important features of the newest model published by ICRP in 1994 (as ICRP Publication 66) are then described, including the morphometric model, physiological parameters, radiation biology, deposition of aerosols, clearance model and dose weighting. Comparison between different morphometric models and comparison between different deposition models are then given. Finally, the significance of various parameters in the lung model is discussed, including aerosol parameters, subject related parameters, target and cell related parameters, and parameters that define the absorption of radon from the lungs to blood. Dosimetric calculations gave a dose conversion coefficient of 15 mSv/WLM, which is higher than the value 5 mSv/WLM derived from epidemiological studies. ICRP stated that dosimetric models should only be used for comparison of doses in the human lungs resulted from different exposure conditions.     

Lung dosimetry for inhaled long-lived radionuclides and radon progeny

The current version of the stochastic lung dosimetry model IDEAL-DOSE considers deposition in the whole tracheobronchial (TB) and alveolar airway system, while clearance is restricted to TB airways. For the investigation of doses produced by inhaled long-lived radionuclides (LLR) together with short-lived radon progeny, alveolar clearance has to be considered. Thus, present dose calculations are based on the average transport rates proposed for the revision of the ICRP human respiratory tract model. The results obtained indicate that LLR cleared from the alveolar region can deliver up to two to six times higher doses to the TB region when compared with the doses from directly deposited particles. Comparison of LLR doses with those of short-lived radon progeny indicates that LLR in uranium mines can deliver up to 5 % of the doses predicted for the short-lived radon daughters.     

Uncertainty in particulate deposition for 1 microm AMAD particles in an adult lung model

The ICRP 66 lung model may be used to determine dose estimates for members of the public via the inhalation pathway. A significant source of uncertainty in internal dosimetric modelling is due to particulate deposition in regions of the respiratory tract. Uncertainties in estimates of particulate deposition are present because model input parameters have their own inherent variability. These sources of uncertainty need to be examined in an effort to understand better model processes and to estimate better the doses received by individuals exposed through the inhalation pathway. An improved understanding of the uncertainty in particulate deposition will further guide research efforts and improve our ability to quantify internal dose estimates. The ICRP 66 lung deposition model is most sensitive to breathing rate when 1 microm AMAD particles are inhaled by members of the public. Uncertainties in deposition fractions are shown to span an order of magnitude with their distributions varying by gender for a particular lung region. The largest fractional deposition occurs in the deep lung alveolar and extrathoracic regions.     

CFD as a tool in risk assessment of inhaled radon progenies

During the last decade, computational fluid dynamics techniques proved to be a powerful tool in the modelling of biological processes and the design of biomedical devices. In this work, a computational fluid dynamics method was applied to model the transport of inhaled air and radioactive particles within the human respiratory tract. A finite volume numerical approach was used to compute the flow field characteristics and particle trajectories in the lumen of the first five airway generations of the human tracheobronchial tree, leading to the right upper lobe. The computations were performed for breathing and exposure conditions characteristic of uranium mines and homes. Primary radon daughter deposition patterns and energy distributions were computed, exhibiting highly inhomogeneous particle and energy deposition patterns. The results of the present modelling effort can serve as input data in lung cancer risk analysis.     

Uncertainty of the thyroid dose conversion factor for inhalation intakes of 131I and its parametric uncertainty

Inhalation exposures of 131I may occur in the physical form of a gas as well as a particulate. The physical characteristics pertaining to these different types of releases influence the intake and subsequent dose to an exposed individual. The thyroid dose received is influenced by the route through which 131I enters the body and its subsequent clearance, absorption and movement throughout the body. The radioactive iodine taken up in the gas-exchange tissues is cleared to other tissues or absorbed into the bloodstream of the individual and transferred to other organs. Iodine in the circulatory system is then taken up by the thyroid gland with resulting dose to that tissue. The magnitude of and uncertainty in the thyroid dose is important to the assessment of individuals exposed to airborne releases of radioiodine. Age- and gender-specific modelling parameters have resulted in significant differences between gas uptake, particulate deposition and inhalation dose conversion factors for each age and gender group. Inhalation dose conversion factors and their inherent uncertainty are markedly affected by the type of iodine intake. These differences are expected due to the modelling of particulate deposition versus uptake of gas in the respiratory tract. Inhalation dose estimates via iodine gases are very similar and separate classifications may not be necessarily based on this assessment.     

Fatigue life prediction of clutch sleeve based on abrasion mathematical model in service period

To predict the service life of clutch sleeve, major reasons for the change of clearance between the clutch sleeve and shell in service period are analysed. A mathematical model of the clearance is established considering abrasion of the step outside sleeve caused by friction. To determine the size of abrasion, a micro‐convex body model for the friction surface is built. Based on surface fatigue abrasion theory, an abrasion model is established. A life model is established based on the entire abrasion of the sleeve. Fatigue life of sleeve is predicted using the model based on actual surface morphology parameters of the enterprise products. Major factors affecting the abrasion speed are discussed and determined after the prediction result is analysed.     

Implications of human nasal clearance studies for the interpretation of nose blow and bioassay sample measurements

The Smith-Etherington extrathoracic (ET) clearance model has been developed to describe clearance from the human nasal passage as observed for 1.5, 3 and 6 microm monodisperse particles inhaled by participants while sitting or at light exercise. Model parameter values have been determined for 22 sets of nasal clearance data from which typical nasal clearance parameter values have been derived. In this investigation, the faecal excretion of 5 microm activity median aerodynamic diameter (AMAD) Type S 239Pu was calculated for three sets of model parameter values, i.e. typical values and those determined for two experiments that respectively exhibited particularly rapid and slow clearance. The study has shown that a greater fraction of material deposited in ET is cleared to the GI tract, and that this clearance takes place over a longer period than assumed by the Human Respiratory Tract Model for Radiological Protection. The study has also shown that deliberate nose blow sampling might potentially be developed to determine the order of magnitude of intakes.     

Application of a prospective model for calculating worker exposure due to the air pathway for operations in a laboratory

In order to arrive at recommendations for guidelines on maximum allowable quantities of radioactive material in laboratories, a proposed mathematical model was used for the calculation of transfer fractions for the air pathway. A set of incident scenarios was defined, including spilling, leakage and failure of the fume hood. For these 'common incidents', dose constraints of 1 mSv and 0.1 mSv are proposed in case the operations are being performed in a controlled area and supervised area, respectively. In addition, a dose constraint of 1 microSv is proposed for each operation under regular working conditions. Combining these dose constraints and the transfer fractions calculated with the proposed model, maximum allowable quantities were calculated for different laboratory operations and situations. Provided that the calculated transfer fractions can be experimentally validated and the dose constraints are acceptable, it can be concluded from the results that the dose constraint for incidents is the most restrictive one. For non-volatile materials this approach leads to quantities much larger than commonly accepted. In those cases, the results of the calculations in this study suggest that limitation of the quantity of radioactive material, which can be handled safely, should be based on other considerations than the inhalation risks. Examples of such considerations might be the level of external exposure, uncontrolled spread of radioactive material by surface contamination, emissions in the environment and severe accidents like fire.     

PREDICTING REGIONAL LUNG DOSAGES OF A NEBULIZED SUSPENSION: PULMICORT® (BUDESONIDE)

A method for estimating the regional lung dosages of a nebulized suspension is presented and applied to Pulmicort® & lpar;budesonide) suspension (4 ml, 0.5 mg/ml) nebulized with three Pari LC + nebulizers driven by a Pulmo-Aide compressor. The methodology combines experimental measurements of the nebulized aersol with a mathematical lung depositor model By adding medlylene blue as tracer for the water, cascade impaction with UV spectrophotometry is used to characterize the distribution of both budesonide and water in the inhaled droplets. Tidal breathing is simulated experimentally using a breath simulator to estimate the amount of inhaled drug. A valve system allows cascade impaction to occur at a constant flow rate of 28.3 l/min. while inhalation at 18 1/min. occurs through the nebulizer. Lung dosages (as % of inhaled dose) obtained with the methodology are in good agreement with values observed in vivo by previous researchers using pharmacokinetic methods with the LC+ nebulizer and the present budesonide formulation. Budesonide is found to be preferentially contained in the larger droplets, and calculated regional lung dosages show that an assumption of homogeneous distribution of the budesonide in the inhaled droplets is incorrect.