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
目的评价阜外改良心肌保存液(fuwai mod ified solution,FWM),HTK液(h istid ine-tryptophan-ketogluratesolution)和UW液(un iversity of w isconsin solution)对离体鼠心的保存效果。方法20只雄性W istar大鼠随机分为四组(Control组、...目的评价阜外改良心肌保存液(fuwai mod ified solution,FWM),HTK液(h istid ine-tryptophan-ketogluratesolution)和UW液(un iversity of w isconsin solution)对离体鼠心的保存效果。方法20只雄性W istar大鼠随机分为四组(Control组、FWM组、HTK组和UW组),每组5只。Control组切取鼠心后立即移至Langendorff装置灌注1h,其它三组分别用不同的保存液4℃下保存6 h,然后将离体鼠心移至Langendorff装置复灌1 h,测定复灌1h后的心肌含水量变化,并用透射电镜观察复灌1 h后心肌超微结构的改变。结果UW组心肌含水量高于Control、FWM和HTK组,而Control,FWM和HTK三组相比无显著统计学差异(P>0.05)。电镜结果显示,Control组和FWM组心肌超微结构基本正常,HTK组出现心肌超微结构改变,而UW组心肌超微结构改变严重。结论FWM液的心肌保存效果优于HTK和UW液。展开更多
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
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.
文摘目的评价阜外改良心肌保存液(fuwai mod ified solution,FWM),HTK液(h istid ine-tryptophan-ketogluratesolution)和UW液(un iversity of w isconsin solution)对离体鼠心的保存效果。方法20只雄性W istar大鼠随机分为四组(Control组、FWM组、HTK组和UW组),每组5只。Control组切取鼠心后立即移至Langendorff装置灌注1h,其它三组分别用不同的保存液4℃下保存6 h,然后将离体鼠心移至Langendorff装置复灌1 h,测定复灌1h后的心肌含水量变化,并用透射电镜观察复灌1 h后心肌超微结构的改变。结果UW组心肌含水量高于Control、FWM和HTK组,而Control,FWM和HTK三组相比无显著统计学差异(P>0.05)。电镜结果显示,Control组和FWM组心肌超微结构基本正常,HTK组出现心肌超微结构改变,而UW组心肌超微结构改变严重。结论FWM液的心肌保存效果优于HTK和UW液。
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.
