胶乳分离机高速转鼓流体动力学特性

Fluid dynamics characteristic of high-speed drum for latex separator

为研究胶乳分离机转鼓离心流场动力学特性,基于FLUENT二相流模型,模拟了胶乳的分离过程以及转速、橡胶粒径对分离效果的影响,以浓乳的干胶含量为综合特征参数进行模型验证试验,理论分析影响分离速度的因素、碟片内液流的流动状态及轨迹、浓缩极限等问题。模型中设置鲜胶乳体积分数初始值为0.330,浓乳黏度0.038 48 m Pa·s,表面张力系数0.034 N/m,橡胶粒径为5μm,胶清按水的属性设置,碟片间隙为0.5 mm。计算结果表明:转鼓转速为7 250 r/min时,胶乳进入转鼓10 s时橡胶粒子与胶清已呈现明显分离倾向;当转鼓分别为6 750、7 250和7 750 r/min时,浓乳中的干胶体积分数分别为0.588、0.613和0.636,转速越高,干胶体积分数越大,但转速超过7 250 r/min,干胶体积分数的增幅变缓,流体压力和结构应力也将明显增加;在7 250 r/min工作转速下,当胶乳粒径分别取1、2、3、4和5μm时,浓乳中干胶的体积分数分别为0.354、0.392、0.447、0.531和0.601,浓乳中干胶体积分数随粒径增大而增加,轻相出口处因流体涡漩体积分数有一定波动。浓乳干胶含量的仿真结果与实测值高度接近,相对误差为3.83%,由此验证了模型的可靠性。轻/重相分离速度与粒径、转速直接相关,因科氏力轻相/重相轨迹与碟片母线有偏离,胶乳浓缩存在上限,轻/重相出料路径合理,离心去除细微杂质的能力强。研究结果为揭示胶乳离心浓缩机理、优化分离工艺及结构提供了理论参考。

Latex separator is the key part of latex concentrated processing equipment,and belongs to disc separator.Disc separator is widely used in various industrial sectors.At present,the theory research on flow field and structure of separator drum is still not perfect,which results in the lack of theoretical guidance for the optimization of flow field and structure about the drum.To solve this problem and to reveal the latex fluid dynamics characteristics of the drum,the research on the flow field of latex drum was carried out.A mathematical model for the flow field of centrifugal separation was established.Based on FLUENT and two-phase flow model built,the fluid dynamics characteristics were explored through simulation and theoretical analysis.In the simulation of latex separation process,the separation effects under different speeds and different rubber particle sizes were conducted.The test of model validation was carried out in the branch factory affiliated to Guangdong Agricultural Reclamation Rubber Group in Zhanjiang in July 2016.The testing separator was the LX-460 type latex separator whose drum parameters were the basis of the construction of analysis model.The measured dry rubber content as comprehensive characteristic parameter was used to validate the model.Based on the mechanics theory,the factors affecting the separation speed of light and heavy phases,the flow state and fluid flow trajectory within the disc gap,the concentration limit and other aspects were analyzed and discussed.For the parameter setting of the model,the kinematic viscosity of concentrated latex was 0.03848 mP a·s,the surface tension coefficient was 0.034 N/m,the rubber particle size was 5μm,the dry rubber volume fraction of raw latex was 0.33,the latex temperature was 26℃,the disc clearance was 0.5 mm,and the properties of latex skim were set as that of water in material library.The research results showed that：At 7 250 r/min rotation speed of the drum,the dynamic process of latex separation was clearly displayed.The rubber particles showed a tendency of separating from latex skim 10 seconds after fresh latex entered the drum.The dry rubber volume fraction of concentrated latex at light phase outlet completely reached the maximum stable value 120 seconds after latex entered the drum.When the rotational speed was respectively 6 750,7 250 and 7 750 r/min,the simulated dry rubber volume fraction of concentrated latex was 0.587 5,0.612 6,0.635 8 respectively at light phase outlet.The higher the speed,the larger the volume fraction of concentrated latex.But when the speed exceeded 7 250 r/min,the increase in the volume fraction of dry latex grew slow,and the fluid pressure and structural stress would increase obviously.When the latex particle sizes were respectively 1,2,3,4 and5μm,the simulated values of dry rubber volume fraction at light phase outlet were 0.354,0.392,0.447,0.531 and 0.609 at the7 250 r/min speed.The dry rubber volume fraction of concentrated latex increased with the increase of the particle size.The dry rubber volume fraction at light phase outlet had a little fluctuation caused by a vortex.The simulation result was in agreement with the experimental result of concentrated latex.The relative error was 3.83%.The reliability of the analytical model was verified.In addition,the theoretical analysis results showed that the factors that significantly affected the separation speed between light and heavy phases were particle size,rotating speed and turning radius of particles.The trajectory of light and heavy phases between the discs would deviate from the conical disc busbar because of the the Coriolis force effect.With the increase of dry rubber content in the process of centrifugal concentration,the viscosity and the particle resistance increased gradually,the turning radius decreased gradually,and there existed the upper bound for latex concentration.The drum structure would be a reasonable design with shorter light-phase discharging path and longer heavy-phase discharging path.The minimum particle size of 0.05μm would be obtained from the neutral hole by theoretical calculation.The centrifugal removal of tiny impurities was superior.The results provide more theoretical guidance and reference for revealing the mechanism of latex centrifugal concentration,and optimizing separation process and drum structure.