Multifunctional fillers are greatly required for dental resin composites(DRCs).In this work,a spray dryer with a three-fluid nozzle was applied for the first time to construct high-performance complex nanoparticle clu...Multifunctional fillers are greatly required for dental resin composites(DRCs).In this work,a spray dryer with a three-fluid nozzle was applied for the first time to construct high-performance complex nanoparticle clusters(CNCs)consisting of different functional nanofillers for dental restoration.The application of a three-fluid nozzle can effectively avoid the aggregation of different nanoparticles with opposite zeta potentials before the spray drying process in order to construct regularly shaped CNCs.For a SiO_(2)–ZrO_(2) binary system,the SiO_(2)–ZrO_(2) CNCs constructed using a three-fluid nozzle maintained their excellent mechanical properties((133.3±4.7)MPa,(8.8±0.5)GPa,(371.1±13.3)MPa,and(64.5±0.7)HV for flexural strength,flexural modulus,compressive strength,and hardness of DRCs,respectively),despite the introduction of ZrO_(2) nanoparticles,whereas their counterparts constructed using a two-fluid nozzle showed significantly decreased mechanical properties.Furthermore,heat treatment of the SiO_(2)-ZrO_(2) CNCs significantly improved the mechanical properties and radiopacity of the DRCs.The DRCs containing over 10%mass fraction ZrO_(2) nanoparticles can meet the requirement for radiopaque fillers.More importantly,this method can be expanded to ternary or quaternary systems.DRCs filled with SiO_(2)-ZrO_(2)-ZnO CNCs with a ratio of 56:10:4 displayed high antibacterial activity(antibacterial ratio>99%)in addition to excellent mechanical properties and radiopacity.Thus,the three-fluid nozzle spray drying technique holds great potential for the efficient construction of multifunctional cluster fillers for DRCs.展开更多
The sand-driven flow is studied from the continuum viewpoint in this paper. The crux of this work is how to model the stresses of the particle phase properly. By analysing the two-fluid model which usually, works in s...The sand-driven flow is studied from the continuum viewpoint in this paper. The crux of this work is how to model the stresses of the particle phase properly. By analysing the two-fluid model which usually, works in solving gas-particle two-phase .flow,. we find that this model has many. deficiencies for studying the sand-driven flow,even for the simplest case- the steady, two-dimensional fully-developed flow.Considering this, we have proposed the three-fluid model in which the upward particles and the downward-particles ore regarded as two kinds of fluids respectively.It is shown that the three-fluid model is better than the two-fluid model in reflecting the internal structure of the flow, region and the influence of the boundary situations on the flow. and it is advantageous to find an approximate solution in that the main components of the particle-phase stresses can be explicitly expressed by those variables in the three-fluid model.In the end, the governing equations as well as the boundary. conditions for the three-fluid model are provided with a discussion.展开更多
A heat transfer model for three-fluid separated heat pipe exchanger was analyzed,and the temperature transfer matrix for general three-fluid separated heat exchanger working in parallel-flow or counter-flow mode was o...A heat transfer model for three-fluid separated heat pipe exchanger was analyzed,and the temperature transfer matrix for general three-fluid separated heat exchanger working in parallel-flow or counter-flow mode was obtained.It was found that the forms of temperature transfer matrix are similar for heat pipe rows with equal or different heat transfer surface area.Furthermore,by using the temperature transfer matrix of the heat pipe exchanger,the relationship between heat transfer effectiveness θ 1,θ 2 and M,NTU,U,Δt i were derived for the exchanger operating in parallel-flow or counter-flow mode,and a simple special example was adopted to demonstrate the correctness of these relationships.展开更多
【目的】棒销式砂磨机的工作过程存在复杂的气体、液体和固体的三相耦合现象,为了使仿真工况更接近实际工况,构建气-液-固三相耦合仿真模型,提高棒销式砂磨机仿真设计的准确性。【方法】采用离散单元法(discrete element method,DEM)和...【目的】棒销式砂磨机的工作过程存在复杂的气体、液体和固体的三相耦合现象,为了使仿真工况更接近实际工况,构建气-液-固三相耦合仿真模型,提高棒销式砂磨机仿真设计的准确性。【方法】采用离散单元法(discrete element method,DEM)和计算流体动力学(computational fluid dynamics,CFD)分别研究固体相和流体相,并引入流体体积模型(volume of fluid model,VOF)区分流体相所包含的液体相和气体相,分析固体相运动方程、流体相控制方程,确定气-液界面的识别方法和耦合计算方法,制定仿真流程;通过单球落水仿真、颗粒群落水仿真试验分析CFD-DEM-VOF三相耦合模型仿真计算的精度,并进行准确性验证;在设置仿真参数、进行网格划分及其无关性分析基础上,针对棒销式砂磨机的CFD-DEM-VOF三相耦合模型进行仿真试验;对流体速度、颗粒总能量和颗粒的速度的仿真结果进行分析,并通过实验验证仿真结果。【结果】在单球落水仿真试验中,根据CFD-DEM-VOF三相耦合模型的仿真结果与根据Stokes定律的理论计算结果基本吻合;在颗粒群落水仿真过程中,液面上升高度的仿真值与理论值之间的相对误差为1.37%,VOF模型的体积守恒性较好;棒销四面体网格边长小于2 mm、研磨桶四面体网格边长小于2.5 mm时,满足网格独立性的精度要求,同时计算量也较少;随着棒销转速的增大,流体速度、颗粒总能量、颗粒平均速度也逐渐增大;当棒销转速为1400~2000 r/min时,CFD-DEM-VOF三相耦合模型流体速度的仿真与实验结果最为接近;当棒销转速为1400~2200 r/min时,CFD-DEM-VOF三相耦合模型的颗粒总能量仿真值与实验值的最大相对误差为1%。【结论】与仅仅采用流体相、固体相单相模型或固-液两相模型相比,采用CFD-DEM-VOF三相耦合模型设计棒销式砂磨机的计算精度和准确性较高,仿真性能好。展开更多
基金the National Key Research and Development Program of China(2016YFA0201701)the National Natural Science Foundation of China(21878015).
文摘Multifunctional fillers are greatly required for dental resin composites(DRCs).In this work,a spray dryer with a three-fluid nozzle was applied for the first time to construct high-performance complex nanoparticle clusters(CNCs)consisting of different functional nanofillers for dental restoration.The application of a three-fluid nozzle can effectively avoid the aggregation of different nanoparticles with opposite zeta potentials before the spray drying process in order to construct regularly shaped CNCs.For a SiO_(2)–ZrO_(2) binary system,the SiO_(2)–ZrO_(2) CNCs constructed using a three-fluid nozzle maintained their excellent mechanical properties((133.3±4.7)MPa,(8.8±0.5)GPa,(371.1±13.3)MPa,and(64.5±0.7)HV for flexural strength,flexural modulus,compressive strength,and hardness of DRCs,respectively),despite the introduction of ZrO_(2) nanoparticles,whereas their counterparts constructed using a two-fluid nozzle showed significantly decreased mechanical properties.Furthermore,heat treatment of the SiO_(2)-ZrO_(2) CNCs significantly improved the mechanical properties and radiopacity of the DRCs.The DRCs containing over 10%mass fraction ZrO_(2) nanoparticles can meet the requirement for radiopaque fillers.More importantly,this method can be expanded to ternary or quaternary systems.DRCs filled with SiO_(2)-ZrO_(2)-ZnO CNCs with a ratio of 56:10:4 displayed high antibacterial activity(antibacterial ratio>99%)in addition to excellent mechanical properties and radiopacity.Thus,the three-fluid nozzle spray drying technique holds great potential for the efficient construction of multifunctional cluster fillers for DRCs.
文摘The sand-driven flow is studied from the continuum viewpoint in this paper. The crux of this work is how to model the stresses of the particle phase properly. By analysing the two-fluid model which usually, works in solving gas-particle two-phase .flow,. we find that this model has many. deficiencies for studying the sand-driven flow,even for the simplest case- the steady, two-dimensional fully-developed flow.Considering this, we have proposed the three-fluid model in which the upward particles and the downward-particles ore regarded as two kinds of fluids respectively.It is shown that the three-fluid model is better than the two-fluid model in reflecting the internal structure of the flow, region and the influence of the boundary situations on the flow. and it is advantageous to find an approximate solution in that the main components of the particle-phase stresses can be explicitly expressed by those variables in the three-fluid model.In the end, the governing equations as well as the boundary. conditions for the three-fluid model are provided with a discussion.
文摘A heat transfer model for three-fluid separated heat pipe exchanger was analyzed,and the temperature transfer matrix for general three-fluid separated heat exchanger working in parallel-flow or counter-flow mode was obtained.It was found that the forms of temperature transfer matrix are similar for heat pipe rows with equal or different heat transfer surface area.Furthermore,by using the temperature transfer matrix of the heat pipe exchanger,the relationship between heat transfer effectiveness θ 1,θ 2 and M,NTU,U,Δt i were derived for the exchanger operating in parallel-flow or counter-flow mode,and a simple special example was adopted to demonstrate the correctness of these relationships.
