气扫式膜蒸馏传质传热过程

对气扫式膜蒸馏（SGMD）的热量和质量传递机理进行了研究,建立了该过程的热量和质量传递模型,并对模型进行了计算,得出了吹扫气流速、组件长度、进料流速和进料温度对膜通量的影响。通过实验对模型计算结果进行了验证。实验结果表明模型计算值与实验值非常接近。随吹扫气流速的增大,通量先增加然后趋近于平衡。组件长度越短通量越高。进料流速对通量的影响很小,随膜丝内Reynolds数的增加,通量稍有增加,随进料温度的升高,通量呈指数倍增加。     

Theoretical and Experimental Studies on Acetylene Absorption in a Polytetrafluoroethylene Hollow‐Fiber Membrane Contactor

The separation of acetylene from a gas mixture was investigated using a polytetrafluoroethylene hollow‐fiber membrane contactor and 1‐methyl‐2‐pyrrolidinone as absorbent. The effects of the gas velocity, the liquid velocity, the feed gas concentration, and the module length on the acetylene mass transfer were investigated. The results showed that the acetylene mass transfer flux increased with increasing liquid velocity, gas velocity, and feed gas concentration, but decreased with increasing membrane module length. A mathematical model was used to predict the wetting extent of the membrane and the mass transfer resistance in the acetylene mass transfer process. The wetting extent of the membrane was found to increase with increasing liquid velocity and to be effectively restrained with increasing gas velocity. The liquid phase resistance and the wetted‐membrane phase resistance controlled the acetylene mass transfer in the acetylene absorption process. The acetylene absorption efficiency was maintained at 90 % for 114 h of the C₂H₂ membrane absorption–thermal desorption cycle process.     

新型气隙式膜蒸馏组件脱盐过程

利用基于聚丙烯中空纤维膜和聚丙烯中空纤维换热管的新型能量回收式膜组件(AGMD-HF),以70 g·L^-1的氯化钠溶液为研究对象,考察了膜组件长度和膜孔径大小对膜组件脱盐性能的影响。为直接衡量操作条件、组件参数以及温差、浓差极化现象对传质系数的影响,引入总传质系数,并研究进料温度和膜孔径对总传质系数的影响。实验结果表明,总传质系数随着温度的升高、膜孔径的增大而增大,提高膜孔径可有效提高总传质系数,同时可有效提高通量和造水比。通量随组件长度的增大而减小,而造水比增大,因此在应用过程中可综合考虑通量和造水比以便选择合适的组件长度。     

Sweeping Gas Membrane Distillation (SGMD) as an Alternative for Integration of Bioethanol Processing: Study on a Commercial Membrane and Operating Parameters

This article considers the application of the sweeping gas membrane distillation process (SGMD) for direct separation of ethanol-water using a flat sheet PTFE membrane. It also studies the effect of operating parameters including feed concentration, feed temperature, feed flow rate, and sweeping gas flow rate on the permeation flux and selectivity of ethanol/water. The results showed that the increase in feed temperature increases in permeate flux and selectivity. Selectivities of 18.5 to 25 were achieved using dilute feeds within the temperature range of 35 to 55°C. However, by increasing the feed concentration by more than 5 wt.%, the selectivity was decreased. The increase in permeation flux and ethanol selectivity at higher feed flow rates was mainly due to the reduction of polarization effects. Moreover, the PTFE membrane was characterized by AFM. The results showed that the present process could be used as a stand-alone technique for bioethanol process integration.     

陶瓷膜冷凝器用于烟气脱白烟过程的中试研究

将平均孔径5、20和50 nm的管式陶瓷外膜制成膜冷凝器，并搭建膜面积0.3 m²的膜冷凝中试实验装置，开展陶瓷膜冷凝器在烟气水、余热资源回收及脱白烟领域的中试研究。对比采用不同排布方式的两级陶瓷膜冷凝器的水、热回收效果，考察进气相对湿度、进气温度、进气线速度等操作条件和不同孔径陶瓷膜的排布方式对膜冷凝器水通量及水回收率的影响。研究表明，在两级膜冷凝器中，烟气、冷却水均为串联流动时，可得到更高的水、热通量及回收率。过程水通量随进气相对湿度、进气温度、进气线速度的增加而增加；水回收率随进气相对湿度、进气温度的增加而增加，随着进气线速度的增加而降低。在三级膜冷凝器中，采用每级均填充平均孔径50 nm的管式陶瓷外膜的排布方式时，可获得最佳的水、热回收效果；不同孔径陶瓷膜的排布方式对膜冷凝器水回收效果影响明显，对热回收效果影响不大。在各实验工况下，三级膜冷凝器水通量及水回收率最高分别可达38.5 kg·m^–2·h^–1和50.6%。与传统换热器相比，陶瓷膜冷凝器不仅可实现水、余热的同时回收，且其总传热系数为415 W·m^–2·℃^–1，换热效果更佳，并能明显缓解“白色烟羽”等视觉污染。基于陶瓷膜的膜冷凝技术在中试实验阶段展现出良好的回收效果，在资源回收及脱白烟过程有广阔的应用前景。     

Modeling and simulation for direct contact membrane distillation in hollow fiber modules

Direct contact membrane distillation (DCMD) offers an attractive operation for the separation of mixtures at atmospheric pressure with reasonable energy requirement. A new simultaneous heat and mass transfer model in DCMD in a hollow fiber configuration is presented. Flow regime in feed and permeate side, the variations of mean temperature and concentration along the membrane module, the length of the membrane, and various properties of membrane characteristics are taken into account in the present model. A system of nonlinear equations describing the DCMD process is solved numerically for each cell using the FSOLVE coding, which is a built‐in function in MATLAB^® to find the influence of the temperature and velocity of the feed and permeate streams, and the salt concentration of the feed along the module on the permeate flux. The predicted results by the new model show a good accord with a wide range of various experimental results available in the literature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 589–603, 2013     

气态膜吸收法脱除水中氨的传质效果

利用聚丙烯中空纤维气态膜对氨/水分离过程及影响因素进行研究,考察膜两侧液体流速、浓度、温度等工艺条件对传质系数和氨脱除率的影响。研究结果表明：气态膜-化学吸收法对氨/水有很好分离效果;原料液温度和流速的影响较为显著,传质系数随温度升高而升高,而提高原料液的流速,膜通量增加,氨的脱除率却下降,压力降升高;氨的初始浓度对膜通量影响较大,膜通量随初始浓度升高而增大;吸收液中反应物浓度相对于透过氨浓度过量时,吸收液的浓度、流速对传质过程影响较小。     

LIX984N为载体的中空纤维更新液膜中铜的传递过程

以LIX984N为载体,煤油为稀释剂,H2SO4为反萃剂,研究了中空纤维更新液膜过程中铜的传递行为。考察了两相压差、铜离子浓度、两相流速、操作方式以及膜丝有效长度等对传质过程的影响。结果表明:膜丝两侧的操作压差对传质过程几乎没有影响;随着料液相中溶质Cu(Ⅱ)浓度的增大传质通量增大,而反萃相中的Cu(Ⅱ)浓度对传质过程几乎没有影响;传质通量会随着壳程料液流速的增大而增大,但管程侧反萃相的流速对传质过程影响很小;逆流和并流两种操作方式对传质过程的影响可以忽略,而膜丝有效长度的增加会导致单位面积平均传质通量的下降。     

太阳能光热-光电中空纤维真空膜蒸馏系统理论与实验研究

自主设计并搭建了太阳能光热-光电中空纤维膜蒸馏系统,太阳能光热采用面积1.82 m²真空管集热系统,光伏发电采用面积1.63 m²多晶硅电池板。实验方面,研究了不同工况下,热料液在不同流动方式时膜通量的差异;研究了在不同跟踪方式下太阳辐照度对系统性能的影响。结果表明：料液在管程流动的膜通量大于壳程的膜通量,且进口料液温度取50~70℃之间为宜;自动跟踪下膜组件入口温度比非跟踪高2~3℃,可以延长膜蒸馏系统运行时间1~2 h,且在相同的自然环境下,自动跟踪方式最大膜通量8.89 kg/(m²·h)远高于非跟踪方式时4.26 kg/(m²·h)。理论方面,分析了以水为工质的中空纤维膜蒸馏的传热和传质过程,建立了传热传质理论计算数学模型;分析了辐照强度、膜表面温差、膜丝内表面传热系数、传热与传质通量的定量关系,计算了膜面温度与理论膜通量,对比了实验值与理论值。系统运行稳定,能量综合利用效率高,性能可靠,为工程应用奠定了理论和实验基础。     

柱式膜组件结构的CFD优化设计

采用Euler模型与多孔介质模型对不同结构的柱式膜组件内的流体流动进行了计算模拟。研究了曝气孔数目（开孔率为1.92%保持不变）与膜组件高度对膜组件膜丝填充区域内的气液两相分布、壁面剪应力、湍流黏度以及液相速度场的影响。计算模拟数据与实验结果吻合良好。计算模拟表明：通过减小曝气孔直径,增加曝气孔数目的方式能够促进气液两相流场与液相速度场的均匀分布,以及壁面剪应力与湍流黏度的增强;增加膜组件的高度,有利于增加单支膜组件膜面积的同时充分利用曝气擦洗过程中气液两相流对膜丝壁面进行高效的气擦洗。综合考虑膜组件的安装运输、膜丝通量分布以及能耗等因素,对于直径250 mm的膜组件采用曝气孔的直径为6.32 mm,数目为30个,长度在2~2.5 m之间为最优。     

Study on a new air-gap membrane distillation module for desalination

A new air-gap membrane distillation (AGMD) module for desalination with internal latent-heat-recovery which consisted of parallel hollow fiber membranes and heat exchange hollow fibers was successfully developed. The influences of feed flow rate, feed temperature and feed initial concentration on AGMD process were investigated. The vapor pressure polarization coefficient (η) was introduced to measure the reduction in the effective driving force for mass transfer with regard to the driving force imposed. Among all AGMD experiments, the maximum water vapor permeate flux (J_D) of 5.30 kg/m² h and the gained output ratio (GOR) of 5.70 were obtained. A theoretical model based on the mass and energy balances of the hot feed side was established to calculate the temperature and the local water vapor permeate flux distributions along the hollow fiber membrane, which showed that the temperature drop and local water vapor permeate flux drop were much larger at the upper part than those at the lower part of the membrane module in the hot feed side.     

减压膜蒸馏传热传质过程

对减压膜蒸馏传热传质机理进行了研究,在已有理论模型的基础上,考虑温度极化和浓差极化的影响,引入减压膜蒸馏传热传质理论模型,并对模型进行了计算,结果表明:随温度的升高,传质系数Km升高,温度极化系数TPC减小,浓差极化系数CPC增大,通量呈近指数倍增加;随流速的增加.TPC增大,膜表面传热系数hf增大,CPC略有降低,K...     

Energetic Performance and Permeate Flux Investigation of Direct-Contact Membrane Distillation for Seawater Desalination

The performance of the direct-contact membrane distillation (DCMD) process in desalting Mediterranean seawater was investigated. Theoretical and experimental optimization of various operating parameters was conducted. The effects of temperature differences, feed velocity, and membrane characteristics were studied. When using commercial polyvinylidene fluoride membranes, the vapor transfer throughout the membrane pores is dominated by the Knudsen-molecular diffusion model. Maximum permeate flux was obtained when increasing temperature, feed velocity, membrane pore size, and porosity and decreasing membrane tortuosity and thickness. Thermal efficiency, gained output ratio, and specific thermal energy consumption were improved when increasing feed temperature. By application of the DCMD process to Mediterranean seawater, a high water quality was obtained.     

直接接触式膜蒸馏过程的膜曝气强化

针对直接接触式膜蒸馏（direct contact membrane distillation,DCMD）过程存在的膜通量小及膜污染问题,设计了一种新型结构的膜蒸馏组件。以蔗糖溶液为处理液,考察了膜组件装填密度Φ、膜曝气量q、蔗糖浓度c与温度T₀对DCMD过程的影响。结果表明：随着Φ、q的增加,DCMD过程的膜通量先增大,后逐渐降低,Φ、q均存在最优值;随着c的增加,膜通量逐渐降低;随着T₀的增加,膜通量增大;对c为30%（mass）的蔗糖溶液进行DCMD法处理330 min时,膜曝气可使DCMD的初始膜通量J_initial提升24.7%、膜通量衰减率ΔJ降低55.0%,维持高膜通量的连续运行时间t₀延长4倍。主要原因是膜曝气强化了DCMD过程的传热传质,进而强化过程的分离性能;有效控制了DCMD过程的浓差极化,进而延缓过程的膜污染进程。研究结果有利于推进DCMD的工程化应用。     

不凝气体对蒸汽射流冷凝的影响

对含不凝气体蒸汽射流在冷水中直接接触冷凝现象进行了实验研究,通过测量流场中的温度分布确定汽羽长度,进而推导其传热系数。实验使用直径为1.6 mm的圆形喷嘴,出口混合气体质量流量密度在100~330 kg·m^-2·s^-1之间,不凝气体的含量在0~15%之间,冷水温度在300~340 K之间。实验结果表明:不凝气体的加入,使喷嘴出口附近的温度下降减慢;汽羽长度随不凝气体含量的增加而变长,其受喷嘴出口质流密度和过冷度的影响规律与纯蒸汽射流一致;冷凝传热系数在0.7~2 MW·m^-2·K^-1之间,随过冷度的增大和不凝气体含量的增加而减小,受气体流量的影响较小。对实验数据进行拟合,获得了汽羽长度的关联式,并由此得到了冷凝传热系数关联式。     

Influence of temperature drop by phase transition on pervaporation processes in vapor phase feed

In this study, pilot pervaporation experiments of ethanol dehydration from the vapor phase feed have been carried out. The dehydration time decreased with increasing of the feed temperature and did not vary with the feed flow rate. The temperature dependence of permeation rate in vapor phase feed was larger than that in liquid phase feed. Contrary to the pilot pervaporation of liquid phase feed, the higher the feed flow rate, the larger the temperature drop is. The variation of temperature drop with permeate flux in vapor phase feed is larger than that in liquid phase owing to the heat loss of the membrane module itself.     

氯乙烯预热器的优化选择

通过对预热器的各组分气体流量、气体温升等相关数据的测量,根据热量衡算计算出混合气体流速、总传热系数、热效率。比较分析了三者之间的关系,从而对预热器进行优化选择。     

气液两相流强化卷式纳滤膜分离硫酸镁水溶液

气液两相流强化卷式纳滤膜分离实验是针对DK2540卷式纳滤膜,采用气液两相流强化分离技术,对硫酸镁溶液进行研究,较系统地研究了温度、料液浓度、过膜压力、料液流速、气体流速等因素在分离硫酸镁溶液时,对膜通量、截留率和膜通量增加率的影响,并总结了气液两相流强化效果。结果表明,气液两相流强化卷式纳滤膜分离有明显的效果。温度宜在30~40℃。料液浓度越大、过膜压力越小、气液比越大,气液两相流强化效果越明显。     

Heat transfer in the rectangular cross-flow flat-sheet membrane module for vacuum membrane distillation

This paper presents a study of heat transfer coefficients of boundary layers in a laboratory-scale rectangular cross-flow flat-sheet membrane module by using distilled water vacuum membrane distillation (VMD) experiments. Results show that the traditional heat transfer correlations, which are mostly employed in the membrane distillation literature, are not suitably used to predict the heat transfer process in the VMD system for the Reynolds numbers ranging from 300 to 1090. This study formulates a new semi-empirical heat transfer correlation by suggesting Knudsen-viscous mechanism governs the water vapour across the membrane. Compared to the feed flow rate, the feed temperature is the limit to the heat transfer. The heat transfer coefficients are strongly dependent on the physical properties of the feed solution, but less relied on the design of the membrane module.     

Simulation of Radiant Syngas Coolers and Comparison with Various Arrangements of the Entrained‐Flow Gasifier

A 3D numerical model was developed for studying the multiphase flow and heat transfer process in a radiant syngas cooler (RSC). Realizable k‐? turbulent and discrete random walk models were adopted to simulate gas phase and particle phase flow fields, respectively. The surface temperature of the membrane wall was calculated by heat flux balance equations. The calculated temperature distribution was validated by comparing calculated values with measured data of an industrial RSC. Four different membrane wall arrangements of RSC, namely, ordinary membrane wall (OMW), partial division wall (PDW), annular division wall (ADW), and fin division wall (FDW), were designed for a specific condition.