A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient con...A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient considering the different evaporation behaviors of UWS droplet at different ambient temperatures. A semidetailed kinetic scheme of urea thermolysis is developed based on Ebrahimian's work. Sequentially, the evaporation characteristics, decomposition efficiency of a single UWS droplet and deposit formation are simulated. As a result, the relation of evaporation time, relative velocity, exhaust temperature and droplet initial diameter is presented. Synchronously, it indicates that temperature is the decisive factor for urea thermolysis. Different temperatures result in different deposit components, and deposit yield is significantly influenced by temperature and decomposition time. The current work can provide guidance for designing urea injection strategy of SCR systems.展开更多
UWS （optimized Urea-Water Solution） injection system is required to increase the NH3 conversion efficiency of urea-based SCR （Selective Catalytic Reduction） system of modem automobiles. The focus of the current st...UWS （optimized Urea-Water Solution） injection system is required to increase the NH3 conversion efficiency of urea-based SCR （Selective Catalytic Reduction） system of modem automobiles. The focus of the current study is to do parametric studies by simulation in a three-dimensional model using CFD （Computational Fluid Dynamics） code AVL FIRE. Simulations were carried out to study the characteristics of evaporation and thermolysis UWS considering the effect of injection velocity, duration of injection, injection angle and for different types of injection. In the case of the injection velocities up to 20-50 m/sec, the ammonia concentration continues to increase. It is found that as the duration injection decreases, the concentration of ammonia increases. In case of continuous injection, the flow rate is less which results in lower velocity of injection, lesser atomization and slower evaporation resulting lesser conversion of UWS into NH3. Shorter duration of injection leads better atomization with increased velocity of injection which results in faster evaporation and thermolysis.展开更多
目的:探讨单光子发射计算机断层成像术(SPECT/CT)和正电子发射断层成像术(PET/CT)后处理工作站对SPECT/CT骨定量分析数据进行定量分析结果的一致性,对比不同工作站测量病灶的最大标准摄取值(the maximum standardized uptake value,SUV_...目的:探讨单光子发射计算机断层成像术(SPECT/CT)和正电子发射断层成像术(PET/CT)后处理工作站对SPECT/CT骨定量分析数据进行定量分析结果的一致性,对比不同工作站测量病灶的最大标准摄取值(the maximum standardized uptake value,SUV_(max))、平均标准摄取值(the average standardized uptake value,SUV_(ave))、病灶体积和平均CT值的异同。方法:回顾分析行全身骨显像及定量SPECT/CT显像且在SPECT/CT显像范围内目测不超过2个显像剂浓聚病灶的患者40例。男性23例,女性17例,年龄37~88岁,平均年龄(60.3±10.2)岁,共获得50个病灶。首先,采用“SyngoMI VB10B SPECT/CT工作站”三维(three-dimensional,3D)等高线容积感兴趣区(volume of interest,VOI)测量法,获得SUV_(max)、SUV_(ave)、病灶体积和平均CT值。然后,将数据导入PET/CT后处理工作站“uWS-MI”医学影像处理软件,采用自带的3D椭球体VOI测量法、自适应阈值分割测量法和固定阈值分割测量法进行上述指标的测量,分别比较其与“SyngoMI VB10B SPECT/CT工作站”3D等高线VOI测量法测得的SUV_(max)、SUV_(ave)、病灶体积和平均CT值的差异是否有统计学意义。结果:3D椭球体VOI测量法与3D等高线VOI测量法比较两组病灶SUV_(max)完全一致,但SUV_(ave)(t=9.841,P<0.001)、病灶体积(t=-4.314,P<0.001)和平均CT值(t=12.554,P<0.001)比较差异有统计学意义。自适应阈值分割测量法和固定阈值分割测量法对其中1例患者的毗邻腰椎和骶骨2处病灶无法准确分割。与3D等高线VOI测量法比较,其他39例患者的48处病灶的SUV_(max)完全一致。自适应阈值分割测量法与3D等高线VOI测量法比较,48处病灶的2组SUV_(ave)(t=-0.723,P=0.473)、病灶体积(t=-1.407,P=0.166)和平均CT值(t=-0.735,P=0.466)的差异均无统计学意义。固定阈值分割测量法与3D等高线VOI测量法比较,48处病灶的2组SUV_(ave)(t=2.947,P=0.473)、病灶体积(t=-2.003,P=0.051)的差异均无统计学意�展开更多
为探究影响柴油机排气管尿素水溶液(urea water solution,UWS)雾化效果的因素,搭建了UWS喷射试验台架,通过激光粒度仪测得尿素液滴粒径分布,并运用Rosin-Rammler函数对试验获得的累积粒径分布进行非线性拟合,利用计算流体力学(computati...为探究影响柴油机排气管尿素水溶液(urea water solution,UWS)雾化效果的因素,搭建了UWS喷射试验台架,通过激光粒度仪测得尿素液滴粒径分布,并运用Rosin-Rammler函数对试验获得的累积粒径分布进行非线性拟合,利用计算流体力学(computational fluid dynamics,CFD)软件对柴油机负荷工况、UWS喷射温度和排气管壁温3种不同因素对UWS喷雾雾化特征、NH3浓度分布及液膜形成的影响进行仿真计算。结果表明:低负荷工况下的排气流量和温度低,UWS喷入量少,尿素液滴分解NH3的速率较低,80 ms时刻NH3主要分布在排气管中游;中高负荷工况,排气温度高、UWS喷入量多,有利于尿素蒸发热解生成NH3,该时刻NH3浓度区域偏离轴线,贴近排气管上表面;喷雾液滴粒径随UWS喷射温度的升高而减小,范围在1~12μm,空间内NH3浓度小幅增加,液膜沉积率随喷射温度升高显著降低;排气管壁温对UWS喷雾液滴粒径和蒸发热解速率影响较大,壁温升高加快了液滴粒径减小的速度,当壁面温度为473K时,150ms时刻下液滴粒径主要集中在30μm以下,附着壁面的液膜厚度明显减小直至消失,尿素结晶问题得以改善。展开更多
基金Supported by the National High Technology Research and Development Program of China(2013AA065301)the Fundamental Research Funds for the Central Universities(2016QNA4014)the State Key Laboratory of Clean Energy Utilization at Zhejiang University(ZJUCEU2016006)
文摘A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient considering the different evaporation behaviors of UWS droplet at different ambient temperatures. A semidetailed kinetic scheme of urea thermolysis is developed based on Ebrahimian's work. Sequentially, the evaporation characteristics, decomposition efficiency of a single UWS droplet and deposit formation are simulated. As a result, the relation of evaporation time, relative velocity, exhaust temperature and droplet initial diameter is presented. Synchronously, it indicates that temperature is the decisive factor for urea thermolysis. Different temperatures result in different deposit components, and deposit yield is significantly influenced by temperature and decomposition time. The current work can provide guidance for designing urea injection strategy of SCR systems.
文摘UWS （optimized Urea-Water Solution） injection system is required to increase the NH3 conversion efficiency of urea-based SCR （Selective Catalytic Reduction） system of modem automobiles. The focus of the current study is to do parametric studies by simulation in a three-dimensional model using CFD （Computational Fluid Dynamics） code AVL FIRE. Simulations were carried out to study the characteristics of evaporation and thermolysis UWS considering the effect of injection velocity, duration of injection, injection angle and for different types of injection. In the case of the injection velocities up to 20-50 m/sec, the ammonia concentration continues to increase. It is found that as the duration injection decreases, the concentration of ammonia increases. In case of continuous injection, the flow rate is less which results in lower velocity of injection, lesser atomization and slower evaporation resulting lesser conversion of UWS into NH3. Shorter duration of injection leads better atomization with increased velocity of injection which results in faster evaporation and thermolysis.
文摘目的:探讨单光子发射计算机断层成像术(SPECT/CT)和正电子发射断层成像术(PET/CT)后处理工作站对SPECT/CT骨定量分析数据进行定量分析结果的一致性,对比不同工作站测量病灶的最大标准摄取值(the maximum standardized uptake value,SUV_(max))、平均标准摄取值(the average standardized uptake value,SUV_(ave))、病灶体积和平均CT值的异同。方法:回顾分析行全身骨显像及定量SPECT/CT显像且在SPECT/CT显像范围内目测不超过2个显像剂浓聚病灶的患者40例。男性23例,女性17例,年龄37~88岁,平均年龄(60.3±10.2)岁,共获得50个病灶。首先,采用“SyngoMI VB10B SPECT/CT工作站”三维(three-dimensional,3D)等高线容积感兴趣区(volume of interest,VOI)测量法,获得SUV_(max)、SUV_(ave)、病灶体积和平均CT值。然后,将数据导入PET/CT后处理工作站“uWS-MI”医学影像处理软件,采用自带的3D椭球体VOI测量法、自适应阈值分割测量法和固定阈值分割测量法进行上述指标的测量,分别比较其与“SyngoMI VB10B SPECT/CT工作站”3D等高线VOI测量法测得的SUV_(max)、SUV_(ave)、病灶体积和平均CT值的差异是否有统计学意义。结果:3D椭球体VOI测量法与3D等高线VOI测量法比较两组病灶SUV_(max)完全一致,但SUV_(ave)(t=9.841,P<0.001)、病灶体积(t=-4.314,P<0.001)和平均CT值(t=12.554,P<0.001)比较差异有统计学意义。自适应阈值分割测量法和固定阈值分割测量法对其中1例患者的毗邻腰椎和骶骨2处病灶无法准确分割。与3D等高线VOI测量法比较,其他39例患者的48处病灶的SUV_(max)完全一致。自适应阈值分割测量法与3D等高线VOI测量法比较,48处病灶的2组SUV_(ave)(t=-0.723,P=0.473)、病灶体积(t=-1.407,P=0.166)和平均CT值(t=-0.735,P=0.466)的差异均无统计学意义。固定阈值分割测量法与3D等高线VOI测量法比较,48处病灶的2组SUV_(ave)(t=2.947,P=0.473)、病灶体积(t=-2.003,P=0.051)的差异均无统计学意�
