【作者】 张辉；

【导师】 王志英；

【作者基本信息】 河北工业大学 ， 化学工程（专业学位）， 2017， 硕士

【摘要】 膜蒸馏(MD)是一种膜技术与传统蒸馏方法结合的低能耗、高截留率的液体分离过程,该过程采用疏水微孔膜作为屏障,热侧待处理料液与疏水膜接触,易挥发组分汽化后跨膜传递至膜下游侧,从而达到分离目的。近年来,高性能疏水微孔膜的制备技术报道频现,尤其是高度疏水或超疏水膜的制备研究备受关注。目前对膜蒸馏过程的研究主要集中在操作条件及膜厚、孔径等结构参数对过程的影响研究,而针对疏水微孔膜表面结构参数对过程影响的研究尚未有报道。本文以低浓度盐水的真空膜蒸馏(VMD)过程为研究对象,综合考察了膜表面微观粗糙结构、膜厚、孔隙率、孔径、曲折因子等对VMD过程通量的影响,建立了相应的传递过程模型。VMD传递过程可分为四个步骤:(1)边界层内的对流传递。针对不同流动状态,得到了不同Re范围下的对流传热、传质系数;(2)粗糙膜表面的汽化传递。此过程为总传递过程的控制步骤,引入了微观凸起的平均宽度作为膜表面结构参数,将粗糙膜表面的汽化液体进行微元处理,得到了膜表面粗糙结构上液滴的蒸发传质速率。(3)蒸汽跨膜传递。跨膜传质过程中气体过膜有三种基本传递机制,计算发现三种机制对传质过程都有影响,所以引入尘气模型(DGM),合理处理了Kundsen扩散、分子扩散和粘性流三种传递机制的关系,得到了跨膜传质系数。(4)蒸汽在膜下游侧冷凝收集。膜下游侧压力较低,传质阻力较小,可忽略不计。在一定操作条件下,分别采用具有不同粗糙表面结构的疏水膜进行VMD实验,得到了膜表面结构参数对VMD过程的影响规律。VMD过程通量随粗糙膜表面凸起平均宽度的减小先增大后减小,当凸起平均宽度为15μm,接触角为150°时,通量最大。实验研究验证了模型的可靠性,并确定了模型参数。更多还原

【Abstract】 Membrane distillation(MD),a combination of membrane technology and traditional distillation processes,is a low-energy and high-rejection process of liquid separation.The process was based on hydrophobic microporous membrane as a barrier,the hot side of the material to be treated was in contact with the hydrophobic membrane,and the volatile components were transferred to the other side of the membrane after vaporization,so that the separation effect was achieved.In the recent years,preparations of high properties porous membrane have been more and more.Especially,increasing attentions have been absorbed on preparation of highly hydrophobic or superhydrophobic membranes.At present,the research on membrane distillation process mainly was focused on the influence of operating parameters and membrane thickness,pore size and other structural parameters on the process,and the study ofthe surface structure of hydrophobic microporous membrane during membrane distillationhas not been reported.In this paper,the vacuum membrane distillation(VMD)process of low concentration brine was studied,the effects of membrane surface structure parameters,membrane thickness,porosity,pore size and tortuosity on VMD process flux were investigated,establish the corresponding transfer process model.VMD transfer process was divided into four steps:(1)Convective transfer in the boundary layer.For different flow states,the convective transfer coefficient was obtained in different states.(2)The volatile components were vaporized on the surface of the rough membrane.This process was the control step for the total transfer process.The average width of microscopic bulge was introduced as the membrane surface structure parameters,the vaporized liquid on the surface of the rough film wsa subjected to micro-treatment.The evaporation mass transfer rate of the droplets on the surface roughness of the membrane have been obtained.(3)The vapor transmembrane transfer.There were three basic transfer mechanisms of the gas transfer in the process of transmembrane mass transfer,and itwas found that they can not be neglected.Therefore,the dusty-gas model(DGM)is introduced to deal with the rational relationship between the Kundsen diffusion,molecular diffusion and viscous flow transfer mechanism.The transmembrane mass transfer coefficient was obtained.(4)The vapor was collected on the downstream side of the membrane.The pressure of downstream side of membrane was low,mass transfer resistance was small,could be directly ignored.Under the condition of certain operating conditions,the hydrophobic membrane with different rough surface structure was used for VMD experiment,and the influence of membrane surface structure parameters on VMD process was obtained.The flux of VMD process was increased first and then decreased with the decrease of the average width of the surface of the rough membrane.When the average width of the bulge was 15μm and the contact angle was 150°,the flux was the largest.Experimental results verified the reliability of the model and determined the model parameters.更多还原