简介:一个概括概率的模型在这研究被开发在早期的运动下面预言沉积乘火车,滚动,并且拾起模式。建议模型的新奇是它在它的明确的表达合并床的概率密度功能砍强调,而不是近床的速度变化,到为沉积乘火车上的两流动骚乱和床表面不规则的效果的报道。建议模型在它的明确的表达合并描述床表面不规则的三个参数的集体效果,也就是,相对粗糙,容量的部分和亲戚在活跃的层以内沉积粒子放。模型的另一特色是它为估计电梯提供一个标准并且基于识别联合拖系数提起并且拖对沉积粒子起作用的力量是相互依赖的并且与粒子伸出和收拾行李的密度变化。模型用好、粗糙的沉积的实验室数据被验证并且与以前出版的模型相比。学习结果证明所有检查模型为好沉积数据足够地表演,在沉积粒子有更多的一致阶段和相对粗糙的地方不是一个因素。建议模型特别地适合粗糙的沉积数据,在增加的床不规则被在模型明确的表达介绍的新参数捕获的地方。作为结果,建议模型在粗糙的沉积数据的情况下与另外的模型相比为电梯系数产出更小的预言错误和身体上可接受的价值。
简介:Theresultsofasimplecomputationalmodelfordifferentialsettlingarepresentedillustratingthesignificantrolethatparticlesizedistributionplaysincollisionfrequencyandsedimentationrateofparticlesinaquiescentenvironment.Themodeltracksalargenumberofparticles(order10~5)withlog-normallydistributeddiameters,astheysettleattheirStokessettlingvelocities.Particlecollisionsaredetectedandresultinlargerparticlesthatfallmorerapidly.Anumberofsimplifyingassumptionsaremadeinthemodelinordertoavoidempiricalcorrelationsforphenomenasuchascollisionefficiencyandparticleshape.Thesesimplifyingassumptionswereneededtoisolateandquantifytheroleoftheparticlesizedistribution.Simulatedconcentrationprofilesindicatethat,evenintheabsenceofcollisions,thestandarddeviation(σ_D)oftheparticlesizestronglyinfluencesthebulkmasssettlingrateas,forlargerσ_D,moremassisconcentratedinlarger,fasterfallingparticles.Thecollisionfrequencyisalsoastrongfunctionofσ_D.Foragivenmassconcentrationthecollisionfrequencyfirstincreaseslinearlywithincreasingσ_Dasgreatervariationinparticlesizeleadstogreatervariationinparticlevelocity,andshortertimesforparticlestocatcheachother.Forlargerσ_Dmoremassisconcentratedinlargerparticles,so,foragivenmassconcentration,therearefewerparticlesperunitvolume,increasingthemeandistancebetweentheparticlesandreducingthecollisionfrequency.Theimplicationsoftheseresultsforsedimentationmeasurementusingopticalattenuationtechniquesarediscussed.