膜蒸馏与热电制冷耦合传质通量分析

分析了膜蒸馏与热电制冷耦合关系,获得耦合的充要条件为热电制冷器应提供充足制冷量及较大温差。通过拟合温差和传质通量及冷端冷负荷分析,建立了热电制冷与膜蒸馏过程耦合的热量平衡方程及耦合特性参数方程,定义了耦合特性参数、耦合工况。理论分析表明,随着制冷温度的增大,膜蒸馏通量预测值的最大值先增大后减小,当制冷温度为279.65 K、热腔入口工质温度为362.15 K时取得最大值65.99 kg/(m~2·h)。本文为热电制冷膜蒸馏实验研究奠定了基础。     

水蒸气在超疏水表面上的冷凝传热

用高温裂解法在紫铜基底上制备了疏水性碳纳米管膜,通过对此碳纳米管膜进行氟化处理,改善了表面的疏水性.在室温下,实验测得水在这种表面上的接触角在90°～130°之间.以水蒸气为冷凝介质的冷凝传热实验表明,水蒸气在超疏水纳米材料表面上能形成较好的滴状冷凝,冷凝传热膜系数可达40000 W/(m2·K).与纯粹膜状冷凝相比,冷凝传热系数提高3～4倍.分析表明,此碳纳米管膜所产生的附加热阻只占冷凝传热热阻的千分之一,对冷凝传热膜系数的影响可以忽略.     

空气隙膜蒸馏系统中超声应用研究

首次将超声激励技术用于膜蒸馏系统以提高蒸馏通量,并采用连续和间隙性超声激励研究超声参数对传质传热的影响并探讨其影响机理．结果表明。（１）蒸馏通量随着超声功率的增大而增加;本实验的超声激励可使蒸馏通量提高３０％;连续激励比间隙激励效果好．（２）超声空化、声学流和膜面振动改善了温度和浓度极化并清洗了膜面,这是超声激励提高蒸馏通量的主要机理,其中声学流与空化对温度和浓度极化的改善更为重要．本文还证实了文献１０提出的关于膜蒸馏通量的理论计算公式也适用于有超声激励的情况．     

PIV在膜蒸馏系统流场测量研究中的应用

空气隙膜蒸馏系统热容腔内料液的流动状态直接影响到温度和浓度边界层效应,决定系统的膜通量。本文采用三根沿圆周平均分布的入流管,喷管是鸭嘴形,应用PIV系统测试膜面附近流动状态。在5种喷管中心线与热容腔径向夹角β和3种喷管前端和膜面间距离δ下,测试得到膜面附近的速度场数据,并计算得到涡量场信息。结果表明,所研究的膜组件结构参数β和δ对热容腔内料液的流动状态影响很大,适当的热容腔结构参数可以有效地改善温度极化边界层和浓度极化边界层的影响,增大膜通量。研究结果为空气隙膜蒸馏系统热容腔入流装置的优化设计提供了实验数据和研究经验。     

具有半导体制冷的新型膜蒸馏组件性能实验研究

设计了一种新型的半导体制冷空气隙膜蒸馏系统,将具有半导体制冷的冷腔与膜蒸馏系统的热腔有机地结合起来。实验研究了半导体输入电流、冷却水流量及热液温度对通量的影响。实验表明:冷却水流量900 L/h,输入电流8 A时的冷壁温度平均为5℃,制冷面各测点的温差最大只有0.5℃,制冷面温度均匀;实验工况8~12 A,冷却水流量300L/h时,膜通量随半导体输入电流的增大而增大。本文的研究为小型半导体制冷空气隙膜蒸馏系统的理论与应用研究奠定了基础。     

分子自组装膜表面滴膜共存冷凝传热的研究

本文以不同处理工艺制备十八烷基硫醇自组装膜,研究制备的表面上蒸气冷凝传热过程.结果表明不同的成膜温度,可以实现膜表面上水蒸气冷凝形态从膜状到滴状的过渡.并研究了该表面上滴膜共存状态下的冷凝传热特性,表明过渡状冷凝传热随固液自由能差渐进变化的实质是冷凝形态的渐进变化,表面上冷凝液运动形态的不同也将导致传热性能的改变,并对自组装膜表面上的冷凝传热系数可能随操作时间的增加而回升的现象进行了分析.     

竖直平壁上双组分混合液膜态沸腾换热解析研究

本文应用近似解析方法对双组分混合液在竖直平壁上的膜态沸腾换热进行了理论分析,得到了其平均膜态换热系数的解析计算式,并通过三种典型的双组分混合液例证了传质过程对换热的影响。     

填料型绝热吸收器影响因素实验研究

为了研究绝热吸收器内溴化锂溶液降膜吸收水蒸汽传质强化过程,本文首先建立了溴化锂溶液降膜绝热吸收循环实验台,然后分析了喷淋溶液温度、喷淋溶液流量、喷淋溶液浓度和吸收压力等参数变化对吸收过程传质系数的影响,并得出有指导意义结论.     

膜换湿特性影响因素的数值研究

本文对膜换湿过程进行了分析,建立了相应的物理数学模型,利用相关模型对不同工况下的传质过程进行了数值分析,对影响膜换湿特性的几种因素进行了研究.结果表明,膜内水蒸气扩散系数对于膜换湿有着显著的影响,空气来流速度对膜换湿特性的影响则很小,薄膜吸附类型参数C在较小的情况下,传质通量随C的增大有较显著的增加,而在C>2的情况下,传质通量随C的增大变化很小,趋向于一定值.     

波纹板片上降膜吸收过程的传热传质数值仿真

建立了在连续的竖直波纹板上降膜吸收过程的传热传质数学模型,并进行了无因次化处理和仿真数值计算。给出了溶液液膜内流场、温度场、质量分数分布的计算结果,比较了交叉双尺度波纹板片和当量平板上的吸收传热和传质系数随不同溶液喷淋密度的变化结果,显示出前者具有更好的性能,并讨论了波纹节距对传热和传质系数的影响关系。     

气隙式膜蒸馏中空气隙内流动与换热研究

本文针对膜蒸馏实验中开放式的窄空气隙,研究其内流动与换热机理.研究发现,对于开放式的大宽隙比(120:1)空气隙,即使其厚度仅为 1 mm,也会形成向上流动的流场,其流动状态为层流,温度分布为直线分布.空气隙内按实验结果求得的热流密度大于按导热公式计算的结果.本文给出的数值模拟结果与实验结果吻合较好.     

膜蒸馏装置热容腔流场数值模拟的可行性分析

本文运用CFD软件,采用水作为工质,在第Ⅲ代膜组件基础上,对旋转切向入流空气隙膜蒸馏热容腔内的流场进行了模拟计算,通过数值模拟结果与实验数据的比较分析,验证了针对膜组件热容腔进行理论模拟所设置的物理模型和边界条件是符合实际的,理论模拟值和实验值的误差在20%范围内,其结果较为理想.     

Phase transitions of adsorbed fluids computed from multiple-histogram reweighting

This paper demonstrates the effectiveness of using multiple-histogram reweighting (MHR) to study phase transitions in confined fluids by examining capillary condensation, prewetting, and layering transitions for different systems. A comparison is made with previously published simulations, where available, to establish the accuracy of MHR as applied to inhomogeneous systems. Overlap between adjacent state points is assessed through single-histogram reweighting. Capillary condensation for methane adsorption in slit-like graphite pores exhibits 2D behaviour. Crossover of the effective exponent for the width of the coexistence curve from 2D Ising-like (1/8) further away from the critical point to mean-field (1/2) near the critical point is observed. The reduced critical temperature, the density and the effective value of the exponent for the model system are 0.77, 0.482, and 0.119, respectively, based on a fit to the simulation data. Prewetting transitions are observed for adsorption of Ar on solid CO₂ using model potentials. The wetting temperature is estimated based on the intersection of the pre-wetting and bulk vapour-liquid lines, and also by extrapolation to zero of the difference between the saturation and prewetting chemical potentials. The reduced wetting temperature is estimated to be around 0.69. The reduced prewetting critical temperature, calculated from the disappearance of the two peaks in the density probability distribution, is estimated to be 0.92. The monolayer to bilayer (1-2) transition for propane on graphite is computed over a range of temperatures. Results for the 1–2 layering transition computed from MHR from a small system are in good agreement with grand canonical Monte Carlo simulations for a much larger system.     

考虑毛细滞后效应的未饱和含湿多孔介质传热和传质理论

毛细滞后是未饱和多孔介质中很重要的特性之一。在许多情况下，毛细滞后现象对介质中传热和传质过程有着显著的影响。本文引入最小梯度概念，用以描述多孔体中毛细水运动滞后的定量行为，进而建立了考虑毛细滞后效应的未饱和含温多孔介质传热和传质的系统理论，为进一步定量研究毛细滞后对传热传质的影响打下了理论基础。     

A non-equilibrium molecular dynamics approach to fluid transfer through microporous membranes

The colour field non-equilibrium molecular dynamics method is applied to model fluid transfer between two fluid phases separated by microporous membranes (i.e. pore width ≤ 2 nm). The model is simple. All particles show short range spherical interactions, but reproduce the main features of the experimental phenomenology of molecular sieve membranes. An external force is applied to the fluid particles and, due to the presence of the membrane, a stationary flux across the system results. A range of mass transfer coefficients was investigated and the fluxes were found to be linear with force intensities. The density was found to have a small effect on molecular mobility, while temperature had a more significant effect, showing the features of an activated process. In addition, the changes in these fluxes with the membrane size, and the cross interaction parameters between the fluid and the membrane particles were examined.     

Morphology and Formation Mechanism of Poly(Vinylidene Fluoride) Membranes Prepared with Immerse Precipitation: Effect of Dissolving Temperature

Poly(vinylidene fluoride) (PVDF) membranes were prepared by the immersion precipitation method. The effects of polymer dissolving temperature for the dopes on the morphology, crystallization and performance of prepared membranes were examined. Polymer dissolving temperature was varied from 50 to 120°C. N,N-dimethylacetamide (DMAc) and de-ionized water were used as solvent and non-solvent, respectively. Based on the membrane morphology and the schematic phase diagram of the ternary system, the membrane formation mechanism was analyzed theoretically. The binodal liquid-liquid demixing took place first for the nucleation and growth of droplets in the polymer poor phase; then consequently the spinodal liquid-liquid demixing occurred in the polymer rich phase. The demixings together resulted in the prepared membranes having a cross-section composed of interconnected globule-like particulates with bi-continuous structured surfaces. The dissolving temperature of the dopes had a remarkable effect on the morphology of the cross-section, even when the solution underwent a long time cooling before the demixing. The increase of the diameter of the particulates with the dissolving temperature was theoretically analyzed according to the conditions of the polymeric solution.     

低品位烟气余热回收换热器热力学分析

低品位烟气余热回收过程存在冷凝现象,烟气的放热过程分为显热、潜热两部分。冷凝时,局部热流率和熵产率明显增大;增加水蒸气质量分数、冷却水质量流量和降低烟气入口温度都会导致烟气提前冷凝;存在最优冷却水质量流量使得热回收过程熵产数最小。另外,提出热回收效率评价烟气热回收程度,该指标受冷凝的影响很大。随着烟气中蒸汽质量分数的增加,冷凝过程的影响明显增强,因此,在低品位烟气的全热回收中必须考虑潜热的影响。     

Preparation of Symmetric Network PVDF Membranes for Protein Adsorption via Vapor-Induced Phase Separation

Symmetric network poly(vinylidene fluoride) (PVDF) membranes without a dense skin layer were prepared by vapor-induced phase separation from a PVDF/N,N-dimethylacetamide (DMAc)/water system. The effects of evaporation atmosphere, temperature, and humidity during the preparation of the membranes on their morphologies were investigated by scanning electron microscope (SEM). With low temperature and high humidity, the polymer crystallization mechanism dominated the membrane formation process, and the casting solution formed membranes with symmetric morphologies in the vapor phase containing 0.79% DMAc. The effect of additives on the membrane structure and performance was also investigated. The results of adsorption experiments showed that the binding capacity of bovine serum albumin (BSA) increased with the appearance of a circular network morphology and the decrease of mean pore size of the membrane. With the addition of LiCl to the casting solution, the obtained membrane can adsorb BSA up to 150 μg/cm². Proteins on sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis gels were successfully electro-blotted onto these PVDF membranes. Compared with commercial membranes, the PVDF membranes prepared in this work were more suitable for protein blotting.