溶液除湿/再生过程中场均匀分布原则的探讨

通过分析溶液除湿、再生过程中传热作用与传质作用的相互影响关系,得出:传质驱动力(湿差)和全热换热驱动力(焓差)的变化规律并不一致.传质驱动力场分布越均匀,传质效果越优.除湿过程和以热溶液为热源的再生过程中,传质方向与全热换热方向相同,相同条件下逆流流型的传质效果最优、叉流次之、顺流最差.而以热空气为热源的再生过程中,传质方向与全热换热方向相反,相同条件下顺流流型的传质效果最优、逆流最差.     

HAT循环饱和器数学模型及实验研究

在分析饱和器内的传热传质过程基础上,建立了一维数学模型,并通过引入广义传质系数CC,简化了饱和器的计算过程。经实验验证表明该模型具有较好的精度,可以比较准确的模拟饱和器内加湿过程,并且对含有填料的饱和器也具有通用性。通过计算得到的饱和器性能曲线图对设计和研究饱和器工作性能和传热传质规律有较大帮助。     

余热制冷装置中氨吸收器热、质耦合数值研究

船用柴油机废热品位较高,基本满足吸收式制冷装置的需要。作为吸收式制冷装置中重要的部件,吸收器的合理设计直接决定了制冷系统的综合性能。在对水平管氨降膜吸收器中传质与传热的相互关系进行详细分析的基础上,建立了完全基于热、质耦合传递的二维模型。数值计算结果表明,在氨降膜吸收过程中,强烈的传质过程是实质,起着主导作用,而传热过程仪是传质过程的外在表现。     

生物质燃料层热解过程的传热传质模型研究

通过分析生物质热解过程的传热传质特点,建立了生物质燃料层热解过程的传热传质教学模型。通过数值计算,研究了生物质燃料层在热解过程中所发生的热量和质量迁移现象,分析了热解过程生物质床内部温度场的分布、生物质固体密度的变化和热解区的迁移规律。     

中空纤维膜管内LiBr溶液除湿过程的数值研究

为研究中空纤维膜和吸湿溶液结合进行制冷预除湿过程的传质机理,建立了膜管外的水蒸气通过膜孔最后被溴化锂溶液吸收传质过程的数值模型,研究了液体进口流速、进口浓度和进口温度对管内溶液的温度分布、质量分数分布和膜孔内水蒸气质量分数分布的影响,并比较了这三种因素对传质的影响程度。在一般预除湿用疏水性膜组件的内部溶液压力条件下(小于10kpa),溶液与水蒸气的接触面在疏水性膜内壁表面。溶液流速的增大,溶液进口质量分数的增大以及溶液进口温度的降低均有利于传质进行,其中,提高溶液进口质量分数对加强传质最为有效。     

基于有限元方法的溴化锂降膜吸收传热传质的数值研究

吸收器是吸收式制冷系统的重要部件。溴化锂溶液的降膜吸收是吸收器中最常见的传质传热形式之一。通过对溴化锂溶液在降膜吸收过程中传质和传热特性的分析,使用基于有限元法的COMSOL Multiphysics软件,建立了溴化锂溶液和水蒸汽降膜吸收的物理数学模型,计算了液膜内部温度和质量分数的分布、界面处传质通量、界面处传热通量、传质传热速率和液相传质传热系数。根据计算结果分析了喷淋密度对平均传质通量、平均传热通量和平均传质传热系数的影响。结果表明:平均传质系数和平均传热系数均随着喷淋密度的增大而增大;平均传质通量和平均传热通量均随喷淋密度的增大而先增后减。     

质子交换膜燃料电池的多尺度传热传质

介绍了目前质子交换膜燃料电池(PEMFC)在膜、电极、单电池、电堆或系统等四个结构尺度上的传热传质过程研究;主要讨论了PEMFC内的多组分传输、膜内水管理和多孔电极内的传热、传质过程;认为建立在孔尺度水平的研究方法是深入探讨电池内多孔材料微结构传热传质的有效途径;多维、多尺度模型的建立及其模拟计算能准确反映PEMFC内部的传递过程机理,为进一步优化电池结构和操作条件提供有价值的参考。     

微尺度催化燃烧过程中传质准则数分析

在微尺度燃烧过程中,由于在很小的范围内各种中间组分和燃烧产物的传质和传热过程以及化学反应过程相耦合,因此微燃烧室内部的对流传质问题比较复杂.基于金属Pt壁面催化微燃烧室的模拟结果,分析了燃烧化学反应过程中组分OH的浓度梯度、传质和流动过程的计算结果,并结合无量纲分析法,推导出传质准则数舍伍德数Sh的数学表达式,通过OH的截面平均Shx去表征微燃烧过程中空间气相反应的变化,并分析入口参数对Shx的影响及空间气相反应与表面催化反应之间的抑制作用.     

喷淋式烟气脱碳传质过程的半经验模拟与分析

为进一步精确建立基于喷淋式的烟气脱碳传质模型,探究不同吸收剂和气液进口参数对传质性能的影响,基于双膜理论,以实验数据为基础建立烟气脱碳气相总传质系数的半经验模型,并探究其与气液流动相关参数的定量关系.结果 表明:流场湍动和界面扰动对液相过程传质的影响不可忽略;所提出的半经验模型在变化趋势和数值上均能有效表征气液进口参数对传质过程的影响;在此基础上,进一步建立了修正系数与操作参数间的无因次幂律关联模型,其拟合优度R2为0.948;结果可为喷淋式烟气脱碳设备的性能预测和评价提供理论参考.     

沿垂直壁面气-液降膜流动传质过程的数值研究

在考虑气-液两相间质量源项和能量源项的条件下,基于VOF算法,建立了水和空气沿竖直平板壁面两相降膜流动传热传质的CFD模型。利用该模型研究了水和空气两相间的传质特性,分析了液膜波动、进气进液速度以及温度对传质的影响,计算结果表明:一定程度的液膜波动、进气速度和进液速度的提高、气-液之间的温差的增加,都能强化气-液之间的传质过程。     

Analysis of a counter-current vapor flow absorber

Analytical investigation of a combined heat and mass transfer process in a counter-current ammonia-water based absorber is presented. The model accounts for both liquid and vapor phase mass transfer resistances, and uses empirical correlations to predict the heat and mass transfer coefficients. The model was used to analyze a lamella plate based absorber with falling film absorption. A finite difference technique was employed to solve the numerical model. It was found that the major portion of the mass transfer resistance lies primarily in the liquid phase. A parametric analysis was also conducted to assess the effect of various parameters on the performance of the absorber.     

Direct numerical simulation of interphase heat and mass transfer in multicomponent vapour–liquid flows

A Volume-of-Fluid methodology for direct numerical simulation of interface dynamics and simultaneous interphase heat and mass transfer in systems with multiple chemical species is presented. This approach is broadly applicable to many industrially important applications, where coupled interphase heat and mass transfer occurs, including distillation. Volume-of-Fluid interface tracking allows investigation of systems with arbitrarily complex interface dynamics. Further, the present method incorporates the full interface species and energy jump conditions for vapour–liquid interphase heat and mass transfer, thus, making it applicable to systems with multiple phase changing species. The model was validated using the ethanol–water system for the cases of wetted-wall vapour–liquid contacting and vapour flow over a smooth, stationary liquid. Good agreement was observed between empirical correlations, experimental data and numerical predictions for vapour and liquid phase mass transfer coefficients. Direct numerical simulation of interphase heat and mass transfer offers the clear advantage of providing detailed information about local heat and mass transfer rates. This local information can be used to develop accurate heat and mass transfer models that may be integrated into large scale process simulation tools and used for equipment design and optimization.     

Experimental and Numerical Study on Heat and Mass Transfer of Cross-Flow Liquid Desiccant Dehumidifier/Regenerator

Abstract

A liquid desiccant air dehumidification system driven by heat pump was established. The performance of cross-flow dehumidifier/regenerator was experimentally investigated. The empirical correlations of Sherwood number for dehumidification/regeneration were obtained by fitting the experimental data. On the basis of the empirical correlations of Sherwood number and thermodynamics analysis of heat and mass transfer process for dehumidifier/regenerator, a cross-flow heat and mass transfer model was established. The effects of air and solution parameters on the dehumidification/regeneration performance were analyzed. The number of mass transfer units and the height-to-length ratio of the packing module were also studied. The results show that there exist optimal number of mass transfer units and height-to-length ratio in the dehumidifier/regenerator.     

Numerical prediction on the erosion in the hearth of a blast furnace during tapping process

The erosion caused by mass transfer in hearth is the most important factor for determining blast furnace campaign life. To support a helpful insight information of mass transfer for the hearth of the No. 2 blast furnace at CSC (China Steel Corporation), a numerical model including the mass transfer of carbon in thermal convective flow from a blast furnace hearth has been developed during the steady tapping process (based on a uninterrupted tapping process assumption). The three dimensional Navier–Stokes equation combined with the transport equations of energy and species with conjugate heat transfer and physical dissolution source is solved by the finite control volume scheme subjected to the segregated iterate under propriety boundary conditions. The results showed the concentration distribution of carbon expressed in terms of mass flux for analyzing the erosion of carbon brick in the blast furnace hearth with the different conditions including the status of dead-man, production of liquid iron, carbon concentration at the inlet, and porosity distribution in coke zone during tapping process at steady state. The result is useful to mitigate the erosion caused by mass transfer, and prolong the life span of the blast furnace.     

FINITE ELEMENT ANALYSIS OF COUPLED HEAT. MASS,AND PRESSURE TRANSFER IN POROUS BIOMATERIALS

Abstract

The finite element method was used to solve Luikov's system of partial differential equations for neat, mass, and pressure transfer in capillary porous bodies. The finite element predictions were validated by comparing with exact solutions and the analytical results given by Mikhailov and Shishedjiev [1]. An application of the finite element method to the drying of wood (spruce) and a comparison based on an eigenvalue solution for simultaneous heat and mass transfer [2] are also provided. This technique was applied to study the coupled transport process in a silicon gel. The simulation indicated that the results obtained from the heat, mass, and pressure transfer model showed a marked difference from the results obtained by the heat and mass transfer model.     

Numerical simulation of a closed wet cooling tower with novel design

A closed wet cooling tower with novel design was proposed and numerically investigated. The studied cooling tower consists of two main parts: one heat and mass transfer unit (HMTU) and one heat transfer unit (HTU). In the HMTU, copper tubes are arranged as heat transfer tubes while plastic tubes are collocated to enlarge the mass transfer area between the spray water and the airflow. In the HTU, only copper tubes are adopted as heat transfer tubes. Heat and mass transfer process takes place among the process water, airflow and spray water in the HMTU, while in the HTU only heat transfer between the process water and the spray water is observed. A transient one dimensional distributed-parameter model was adopted to evaluate the cooling tower performance under different operating conditions. Determination of heat and mass transfer coefficients, as well as the influence of Lewis number on the cooling tower performance, was presented.     

固着液滴蒸发研究进展及展望

固着液滴是指附着于壁面上的液滴,其蒸发行为及传热传质特性是喷雾冷却、喷墨打印等相变传热传质领域的基础问题之一。文中重点针对固着液滴蒸发过程所涉及的自身形态演变规律、气液固三相耦合传热/传质/流动特性进行了综述。结合毫微尺度固着液滴基本蒸发模式、热质传递形式、气液两相流动特征和界面输运行为,分析了液滴性质、壁面条件、气相环境条件等关键因素对固着液滴蒸发过程的内在作用机制和影响规律,提出了微纳尺度固着液滴（群）热质传递过程与机理的相关研究展望。     

Effect of regeneration mode on the performance of liquid desiccant packed bed regenerator

The regenerator is one of the key components in liquid desiccant air-conditioning systems, in which desiccant is concentrated and can be reused in the system. The regeneration heat is supplied into the regenerator by either hot air or hot desiccant. The heat and mass transfer performances of these two regeneration modes are analyzed and compared in detail. In the hot air driven regenerator, the parallel-flow regenerator has the best mass transfer performance and the counter-flow performs poorest under the same conditions, because the heat transfer process is the governing process and the mass transfer performance depends on the promotion of the heat transfer to the mass transfer process. In the hot desiccant driven regenerator, counter-flow configuration has the best mass transfer performance and parallel-flow is the poorest at the same conditions, since mass transfer is the governing process. Regeneration heat should be chosen to heat the desiccant instead of the air in the packed bed regenerator, since the hot desiccant driven regenerator has apparent better mass transfer performance. The proposed regeneration mode and flow pattern will be helpful in the design and optimization of the regenerators.     

Handling zone dividing method in packed bed liquid desiccant dehumidification/regeneration process

Dehumidifier and regenerator are the most significant components in liquid desiccant air-conditioning systems, in which air directly contacts liquid desiccant and heat and mass transfer process occurs between the two fluids. Heat transfer process and mass transfer process within dehumidifier/regenerator influence each other and should not be separately considered. Based on the previous reachable handling region analysis, a zonal method is proposed in present study. Four zones are divided in the psychrometric chart according to the relative position of inlet air to inlet desiccant including two dehumidification zones, zone A and zone D, and two regeneration zones, zone B and zone C. In zone A or C, mass transfer is key process, and counter-flow configuration has the best mass transfer performance and parallel-flow is the poorest in the same operating conditions. In zone B or D, heat transfer is governing process, parallel-flow has the best mass transfer performance and counter-flow is the poorest. In order to obtain better mass transfer performance, liquid desiccant should be cooled (in zone A) rather than air (in zone D) in dehumidifier, and liquid desiccant should be heated (in zone C) rather than air (in zone B) in regenerator. The divided zones and the corresponding zonal properties will be helpful to the design and optimization of dehumidifiers and regenerators.