Modeling and simulation of urea-water-solution droplet evaporation and thermolysis processes for SCR systems

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.

Unusual dinosaur trackway preservation as clues to paleo-landscape and behavior from the Lower Cretaceous Luohe Formation,Shaanxi Province,China

Poorly preserved tracks have limited ichnotaxonomic or biotaxon utility,but may reveal useful information about the paleoenvironment,behavior and track taphonomy.Eight mostly parallel to sub parallel trackway segments(T1–T8)were registered on a truncation surface in the Lower Cretaceous Luohe Formation of Shaanxi Province.These attest to the passage of several bipeds,probably all theropods,in a paleo-contour-parallel,south-north direction in an arid setting.Quality of preservation in these trackways is poor,but notably superior in two additional trackways(T9–T10)on a foreset surface.Trackway T9 indicates a didactyl trackmaker,probably a deinonychosaurian,heading north to south.This is the 13th report of deinonychosaurian tracks from the Lower Cretaceous of China.If any or all the eight south-north oriented trackway segments represent continuations of other segments in the same trackways,the total number of individual trackmakers heading in this direction may have been as lowas three.Although the trackway pattern and sedimentological evidence could indicate a physically controlled pathway influencing the direction taken by these trackmakers,the possibility that the trackways also represented small social or gregarious group cannot be ruled out.

Researches on preconditioned wire arrayZpinches in Xi’an Jiaotong University

The dynamics of wire array Z pinches are greatly affected by the initial state of the wires,which can be preconditioned by a prepulse current.Recent advances in experimental research on preconditioned wire array Z pinches at Xi’an Jiaotong University are presented in this paper.Single-wire explosion experiments were carried out to check the state of the preconditioning and to obtain the current parameters needed for wire gasification.Double-wire explosion experiments were conducted to investigate the temporal evolution of the density distribution of the two gasified wires.Based on the results of these experiments,a double-pulse Z-pinch facility,Qin-1,in which a 10 kA prepulse current was coupled with the 0.8 MA main current was designed and constructed.Wire arrays of different wire materials,including silver and tungsten,can be preconditioned by the prepulse current to a gaseous state.Implosion of the two preconditioned aluminum wires exhibited no ablation and little trailing mass.

Convection effect on an arc plasma evolution process in a two parallel contact system

A low voltage circuit breaker(LVCB)is an important piece of protection equipment which will switch off the fault current in a power system.The moving contact of a low voltage circuit breaker with a higher rated current consists of two parallel contacts.Therefore,the convection effect on the air arc evolution process in a two parallel contact system is analyzed.A threedimensional(3 D)magneto–hydro–dynamic(MHD)model of arc simulation is built.In this model,the anode consists of two parallel contacts and a bonding conductor.A nonlinear voltage–current density characteristic is employed to represent the near-anode and near-cathode voltage.The current density,arc voltage and currents through every contact are obtained.The influence of convection and conduction on the arc evolution process are quantitatively calculated.The displacements of the arc roots are obtained and the asymmetry of the arc root motion is analyzed.The arc evolution process of a two parallel contact system is preliminarily revealed.

Editorial for special issue on Z-pinches

Fast Z-pinches,plasma implosions driven by MA-level∼100-ns duration current pulses,are an active research area with applications to a broad range of High Energy Density Physics studies,including investigations of properties of materials at extreme pressures,1 opacities of various plasmas at conditions found in stellar interiors,2 and scaled modelling of astrophysical magnetohydrodynamics.3 The ability of fast Z-pinches to generate extremely bright pulses of X-ray radiation is of significant interest for Inertial Confinement Fusion(ICF)studies.The highest X-ray powers and yields are achieved using wire-array Z-pinch loads,which are capable of generating 2-MJ,250-TW,<10-ns X-ray pulses at the largest currently operating pulsed power facility,the 25-MA Z machine at Sandia National Laboratories(New Mexico,USA).