【作者】 李振兴；

【导师】 张立志；

【作者基本信息】 华南理工大学 ， 化学工程， 2014， 博士

【摘要】 室内空气湿度对人们的生活与生产密切相关。控制湿度在合适的范围有益于人的身心健康，并有利于生产安全。近年来，膜式组件在室内湿度调节中起到不容忽视的作用。膜式组件按膜的形态与流道结构可以分为平行板式、板翅式、中空纤维膜式与交叉三角形波纹板式。其中以中空纤维膜式与交叉三角形波纹板式膜组件内的传递现象最为复杂。中空纤维膜组件的结构类似于管壳式换热器，管程液态水和壳程空气通过中空纤维膜进行热湿交换。中空纤维膜材料为选择性渗透膜，可以截留液态水而仅允许水蒸汽透过。交叉三角形波纹板式膜组件结构类似于波纹板式换热器，新风与排风空气通过膜进行热湿交换。交叉三角形流道可以有效强化组件的热质传递能力。膜表面的共轭边界条件与组件内的流动分布对组件的性能起到重要的影响。而这两种因素的作用正是现有研究在建立数学模型时所忽视的。为揭示中空纤维膜组件与交叉三角形波纹板式膜组件内的热质传递机理，本文以加湿组件为例建立了相应的数学模型：(1)管束按规则排列的错流中空纤维膜组件。以周期性的三角形排列与四边形排列管束为研究对象，建立了壳程动量与质量守恒方程，膜表面采用恒定浓度边界条件，求解获得了舍伍德数与阻力系数等准则数，采用加湿实验结果验证了模型。结果表明，在中空纤维膜管束以三角形排列时，由于管束间的冲击与分离作用，流场内的扰动更强烈，其传质系数与阻力系数均大于同样管间距比下四边形排列管束的值。管束填充率越高，组件的传质系数与进出口压降越大。管束的管间距比对组件传质与阻力特性也有较大影响。其中纵向管间距比对组件性能的影响要比横向管间距比更明显。(2)管束按随机排列的逆流中空纤维膜组件。选取有限根随机排列的中空纤维膜为研究对象，建立了空气侧与水侧动量与质量守恒方程，膜表面采用共轭边界条件，求解获得了努谢尔数、舍伍德数与阻力系数等准则数，采用加湿实验结果验证了模型。结果表明，管束分布的随机性使管束的外流场速度分布恶化严重。这种流动分布不均匀性使得随机排列的管束较规则排列管束的热质传递性能有明显降低。而膜表面的共轭边界使这种恶化作用更大，相应的对流传热传质系数比理想边界条件下更低。(3)中空纤维膜组件内的流动分布不均匀性。将中空纤维膜管束近似简化为多孔介质来求解组件内的流动分布。然后利用热湿守恒方程求解流动分布不均匀性对组件内温湿度场分布的影响，从而计算得到组件冷却效率与加湿效率受流动分布不均匀性的恶化作用。结果表明，壳程进出口效应对组件内的流动分布有重要影响。这种流动分布不均匀性经中空纤维膜管束进一步得到放大。膜组件的填充率越高，组件内的流动分布越均匀。对于填充率范围为0.1-0.3的错流膜组件，与速度均匀分布的情况相比，其冷却效率降低可达3-30%，而加湿效率降低可达26-58%；对于填充率范围为0.1-0.3的逆流膜组件，其冷却效率降低可达3-36%，而加湿效率降低可达5-39%。(4)交叉三角形波纹板式膜组件。选取有限层交叉三角形波纹板流道为研究对象，建立了空气在流道内的动量、热量与质量守恒方程，并将热湿守恒方程通过膜上边界耦合起来求解，最终获得流道的努谢尔数与舍伍德数。实验中通过使用一步法制备的非对称醋酸纤维素膜增强组件的传质性能。并将采用不同流道结构或不同膜材料的组件进行了性能比较。结果表明，流道顶角越大，流道内速度分布越均匀，流道的传热传质能力越大。流道顶角越小，共轭边界条件下的对流传热传质系数较理想边界下越小。相对于采用复合膜制备的平行板与板翅式全热交换组件，采用非对称膜制备的交叉三角形波纹板全热交换组件的显热效率可以提高20%左右，潜热效率提高40%左右。另一方面由于流道结构的差异，交叉三角形波纹板流道的阻力系数是前两者的1.5-4倍。更多还原

【Abstract】 Indoor air humidity is closely related to people’s life and industrial production. It isbeneficial for human health and production safety to manage indoor air humidity in a properrange. In recent years, membrane modules play an important role in humidity control.According to the shape of the flow channel, membrane modules can be divided intoparallel-plate membrane module, plate-fin membrane module, hollow fiber membrane moduleand cross-corrugated triangular duct membrane module. The transport phenomenon isespecially complex in the latter two types. Hollow fiber membrane module has a structuresimilar to a shell-and-tube heat exchanger, water vapor in lumen side and air in shell side canexchange heat and moisture through the membrane. The membrane has a selectivity toprevent liquid water from permeating but allow water vapor to permeate. Cross-corrugatedtriangular duct membrane module has a structure similar to chevron plate heat exchanger.Fresh air and exhaust air exchanges heat and moisture through the membrane. Thecross-corrugated triangular duct can effectively enhance heat and mass transfer in the module.The conjugate boundary condition on the membrane and flow maldistribution in the modulehave significant effect on predicting module’s performance. However, these two elements areusually ignored in the mathematical model in current researches. To reveal the mechanism ofheat and mass transfer in hollow fiber membrane module and cross-corrugated triangular platemembrane module, mathematical models are established in this work:(1) Cross flow hollow fiber membrane module, ordered array tube bank. A periodic cellcontaining inlined or staggered tube banks is selected as research object. Conservationequations in shell side are established, and conjugated boundary condition is applied tomembrane surface. The Nusselt number, Sherwood number and friction factor are obtained.Humidification experimental results are used to verify the model. The results show that masstransfer coefficient and friction factor are higher in staggered tube array due to strongerdisturbance and boundary layer separation. The higher the packing fraction is, the larger themass transfer coefficient and pressure drop is. The pitch to diameter ratio has important effecton mass transfer and resistance characteristic. And the effect caused by transverse pitch todiameter ratio is more evident.(2) Counter-current flow hollow fiber membrane module, random array tube bank. Arepresentative cell containing finite random packed fibers is selected as research object.Conservation equations in shell side and lumen side are established, and conjugated boundarycondition is applied to membrane surface. The Nusselt number, Sherwood number and friction factor are obtained. Humidification experimental results are used to verify the model.The results show that the randomness of the tube array leads to significant flowmaldistribution in shell side. This flow maldistribution deteriorates module’s performancedramatically. Conjugated boundary conditions on the membrane make this deterioration muchhigher.(3) Flow maldistribution in hollow fiber membrane module. To get the flow distributionin the module, hollow fiber membrane bundle is simplified as porous medium. The heat andmass conservation equations are solved to get temperature and humidity distribution in themodule. After that, the effect of flow distribution on sensible cooling and humidificationefficiency can be analyzed. The results show that shell side inlet/outlet effect has effect onflow distribution in the module. The higher the packing fraction is, the more homogeneous theflow distribution is. For a cross flow membrane module whose packing fraction ranges from0.1to0.3, the sensible cooling efficiency can deteriorate by3-30%, and humidificationefficiency can deteriorate by26-58%. For a counter-current flow membrane module whosepacking fraction ranges from0.1to0.3, the sensible cooling efficiency can deteriorate by3-36%, and humidification efficiency can deteriorate by5-39%.(4) Cross-corrugated triangular duct membrane module. A representative cell containingfinite cross-corrugated triangular ducts is selected as research object. Conservation equationsin the flow channel are established, and conjugated boundary condition is applied tomembrane surface. The Nusselt number, Sherwood number and friction factor are obtained.One-step made asymmetric cellulose acetate membrane is used as the exchanger material toenhance mass transfer. The modules’ performance is compared with different flow channelstructures or different membrane materials. The results show that the larger the apex angle ofthe channel is, the more homogeneous the flow distribution is, leading to an enhancement onheat and mass transfer. The smaller the apex angle of the channel is, the more deviationbetween results calculated by conjugated boundary condition and realistic boundary condition.Compared to parallel-plate or plate-fin membrane module fabricated by composite membrane,the cross corrugated triangular duct membrane module fabricated by asymmetric membranecan enhance sensible heat efficiency by20%, and enhance latent heat efficiency by40%.However, due to the complex flow channel structure, its friction factor is about1.5-4times ofthe former two.更多还原