真空膜蒸馏过程膜参数模拟计算

为了研究膜材料对透过通量的影响,文章建立了真空膜蒸馏过程的微观传热传质模型,并利用该模型对文献中的实验数据进行了模拟,得到了比较满意的结果。进而对不同条件下膜的长度、厚度、内径以及曲折因子、传质系数进行了模拟计算,并讨论了不同膜参数对膜透过通量的影响,为真空膜蒸馏过程中膜材料的选取及合理利用提供一定的理论依据。     

水冷却塔传质系数计算模型初探

冷却塔填料表面传热传质过程的理论计算都与一个经验参数——传质系数有关。因为过去人们都将这个参数表示成水气流量的函数,未能正确地反映传质系数对水冷却塔传热传质过程重要影响的本质。采用液膜蒸发理论,将传质系数表示成湿空气温差及压差的函数,新的计算方法将改善冷却塔的设计计算。     

浓水溶液的膜蒸馏行为——Ⅱ.蒸气压下降和透析作用的影响

膜蒸馏的蒸馏通量随溶液浓度的增加而逐渐降低,其实质是传质分数和组件的蒸馏效率随浓度增大而下降。本文近似地计算了理论传质分数,实际透过分数和组件的蒸馏效率在不同温度条件下的变化情况以及浓度变化对它们的影响,从中分析了浓溶液的蒸气压下降对膜蒸馏的影响,讨论了膜蒸馏过程中因渗透压而产生的透析现象的存在以及透析现象对膜蒸馏的干扰作用。     

全钒液流电池与质子交换膜燃料电池中可控的传热传质研究

简述了全钒液流电池和质子交换膜燃料电池系统中通过控制传热传质机理来提高电池系统性能的研究进展。在VRB中主要回顾了温度场、电极、质子交换膜、流场设计及外场对传热传质过程影响的相关研究。关于PEMFC主要介绍了温度、膜电极的有序化、流场设计及重力场对传热传质过程影响的相关研究。总结了这2类电池传热传质过程研究的主要方向,并展望了这2类电池的发展前景。     

LiCl溶液垂直管外降膜发生效果的实验

为了探究LiCl水溶液在低位太阳能吸收式制冷系统中的发生过程中的传热传质效果,在降膜发生实验装置基础上研究了LiCl水溶液在垂直管外降膜发生的传热传质过程。阐述了不同运行工况如不同的热水和溶液的流量、热源的温度、溶液的浓度和系统压力对LiCl水溶液发生过程传热传质效果的影响。同时也进行了相同工况下LiBr水溶液的对比实验。结果表明相同运行工况下LiCl水溶液降膜发生过程和LiBr水溶液的降膜发生过程有着相似的变化规律。虽然LiCl水溶液的垂直降膜发生速率略低于LiBr水溶液,但传质效果相差不大,LiCl溶液的低运行浓度有利于循环热力性能的提升。     

LiCl溶液垂直管外降膜发生效果的实验

为了探究LiCl水溶液在低位太阳能吸收式制冷系统中的发生过程中的传热传质效果,在降膜发生实验装置基础上研究了LiCl水溶液在垂直管外降膜发生的传热传质过程。阐述了不同运行工况如不同的热水和溶液的流量、热源的温度、溶液的浓度和系统压力对LiCl水溶液发生过程传热传质效果的影响。同时也进行了相同工况下LiBr水溶液的对比实验。结果表明相同运行工况下LiCl水溶液降膜发生过程和LiBr水溶液的降膜发生过程有着相似的变化规律。虽然LiCl水溶液的垂直降膜发生速率略低于LiBr水溶液,但传质效果相差不大,LiCl溶液的低运行浓度有利于循环热力性能的提升。     

低温膜蒸馏及其过程模拟

采用聚丙烯中空纤维膜对纯水介质膜蒸馏、冷侧盐水循环有温差膜蒸馏及等温渗透膜蒸馏进行了实验研究,建立了描述膜蒸馏过程的传质及传热数学模型,以实验数据为基础对模型中的参数进行了回归并对数学模型进行了计算机数值求解,计算结果与实验数据吻合较好     

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。     

气隙式膜蒸馏传递过程的研究

本文用气隙式膜蒸馏装置测定了膜两侧流体的温度、流量及料液浓度对膜蒸馏通量的影响,并从理论上描述了传热、传质过程,建立了可以预测膜蒸馏过程渗透通量的数学模型.实验结果与模型预测吻合较好.     

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...     

Effect of Pressure on Moisture Transfer During Moisture Adsorption

ABSTRACT

A set of coupled heat, mass, and pressure transfer equations was used to describe the moisture adsorption process in gmn kernels. The finite element method was used to solve the system of equations. The technique was applied to analyze the temperature, moisture, and pressure distribution in a barley kernel during soaking with steep water. The temperature and moisture distributions with (heat, mass, and pressure transfer model) and without (heat and mass uansfer) the effect of pressure were simulated for assumed conditions. The results obtained from the heat, mass, and pressure transfer model show a marked difference from the results obtained from the heat and mass transfer model. This indicated that a pressure gradient exists during the transfer Process, causing additional moisture movement due to filtration effect. Hence. the pressure tern cannot be assumed constant during the moisture adsorption process. The simulated temperature, moisture and pressure profiles and gradients can be used for determining the optimum time required for solking kernels with sleep water to produce barley malt.     

SIMULATION OF THE HEAT AND MOISTURE TRANSFER PROCESS DURING DRYING IN DEEP GRAIN BEDS

ABSTRACT

Grain drying is a simultaneous heat and moisture transfer problem. The modelling of such a problem is of significance in understanding and controlling the drying process. In the present study, a mathematical model for coupled heat and moisture transfer problem is presented. The model consists of four partial differential equations for mass balance, heat balance, heat transfer and drying rate. A simple finite difference method is used to solve the equations. The method shows good flexibility in choosing time and space steps which enable the simulation of long term grain drying/cooling processes. A deep barley bed is used as an example of grain beds in the current simulation. The results are verified against experimental data taken from literature. The analysis of the effects of operating conditions on the temperature and moisture content within the bed is also carried out     

DRYING OF CARROTS. I. DRYING MODELS.

Three models of different complexity are proposed to describe the falling rate period of the carrot drying process with shrinkage. A moving or fixed boundary problem as well as a constant or local moisture and temperature dependent effective diffusivity are considered. The moving boundary problem is solved by an explicit finite difference method. Heat transfer coefficient and effective diffusivity identification were carried out. The results of the heat transfer coefficient show a good agreement with other sources. Using experimental data and the models. describing the heat and mass transfer three different expressions for the effective diffusivity are established. Two of them are only temperature dependent considering or not particle shrinkage. The third one takes into account temperature and local moisture as well as shrinkage.

Drying of foods is a complicated process involving simultaneous coupled heat and mass transfer phenomena which occur inside the material being dried (Chiang and Petersen, 1987). Several models are found in the literature, representing mass and energy transfer which take place during food drying (King, 1968; Sokhansanj and Gustafson, 1980). Usually, approximate solutions are obtained with these     

流化床氛围下多孔物料干燥传热传质的数值模拟

用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法（TDMA）用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明：干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。     

膜蓄能器放能过程的传热传质特性分析

膜构架蓄能器是以中空纤维膜为基本结构，不仅能够实现蓄能，同时能够解决溴化锂溶液浓度差蓄能器中结晶后的放能困难的问题。搭建了膜蓄能器放能过程传热传质实验测试系统，建立了应用于太阳能吸收式制冷系统中的膜架构蓄能器传热传质的三维数学模型，并利用 CFD 软件进行了求解。将计算结果与实验结果相比较，验证了该三维非稳态数学模型的可靠性。实验和仿真结果表明，质量分数为70% 的溴化锂溶液的水蒸气分子平均传质速率比质量分数为60%的溶液高44.03%；当蒸发温度从4.5℃提高到12.3℃时，水蒸气分子的平均传质速率将提高108.34%；当膜通道的有效长度从80 mm减少到30 mm时，水蒸气分子的传质速率会提高40.77%。     

基于亲水/憎水复合膜的全热交换器换热换湿性能[

膜全热交换器由于可以同时回收空调排风中的潜热和显热而受到重视。研究了基于PVAL/PVDF复合透湿膜的全热交换器的透热透湿性能，实验测定了新风与排风之间的显热交换能力和水蒸气交换能力，并建立了基于亲水/憎水复合膜的逆流膜全热交换器传热传质计算模型，实验与理论结果吻合较好。结果表明，该复合膜全热交换器的总传热系数为20～35 W·m-2·℃-1，总传质系数为（1.5～3.5）×10-3 m·s-1。     

Conjugate heat and mass transfer model for predicting thin-layer drying uniformity in a compact,crossflow dehydrator

Abstract

A conjugate heat and mass transfer model was implemented into a commercial CFD code to analyze the convective drying of corn. The Navier–Stokes equations for drying air flow were coupled to diffusion equations for heat and moisture transport in a corn kernel during drying. Model formulation and implementation in the commercial software is discussed. Validation simulations were conducted to compare numerical results to experimental, thin-layer drying data. The model was then used to analyze drying performance for a compact, crossflow dehydrator. At low inlet air temperatures, the drying rate in the compact dehydrator matched the thin-layer drying rate. At higher temperatures, heat losses through the external walls resulted in temperature and moisture variations across the dehydrator.     

Mathematical modelling of an industrial furnace for high‐temperature heat treatment of wood

There are various high‐temperature treatment methods for wood. In the “Bois Perdure” process, the thermal treatment of wood is carried out in a furnace by contacting it with hot combustion gases over 200°C without the addition of any chemicals in order to improve its dimensional stability and durability. The treatment eliminates free and bound water in the wood and modifies its molecular structure. In this study, a mathematical model describing the industrial furnace has been developed. The overall model consists of a 3‐D unsteady‐state sub‐model which solves for the flow, heat, and mass transfer in the gas coupled with a 1‐D unsteady‐state sub‐model which calculates the heat and mass transfer in the wood. The 3‐D gas sub‐model was developed using the commercial CFD code CFX. The 1‐D wood sub‐model is based on the solution of simultaneous heat and mass transfer equations (Luikov equations) using the implicit finite difference formulation. The model predicts the temperature and moisture distributions in the wood as well as the flow, heat, and moisture profiles in the gas. The model results are compared with the data obtained from the industrial furnace, and a good agreement was found between them.     

错流降膜液体干燥剂除湿/再生传热传质数学模型及分析

分析了错流降膜液体干燥剂除湿及再生传热传质过程 ,建立了基于实际除湿系统的描述再生和除湿过程的数学模型 ,考虑到除湿过程中产生的热效应 ,以氯化钙溶液为除湿剂时 ,对气侧和液侧的传热传质系数进行了理论和数值求解 .计算结果表明 ,传热传质系数与气流流动状态、除湿剂的热物理性质等因素有关     

膜式液体除湿器研究进展

膜式液体除湿技术可很好地解决传统气液直接接触填料塔式液体除湿技术中存在的除湿溶液液滴夹带问题。在膜式液体除湿技术中,湿空气和除湿溶液被半透膜隔离。该膜只允许水蒸气的透过,而严格阻止其它气体和液体的渗透。本文概述了膜式液体除湿器中常用膜材料和膜组件的研究进展,重点阐述了膜式液体除湿器中的热质共轭传递数学模型,展望了膜式液体除湿器的发展方向。容易发现,在膜材料方面,在防止溶液泄露的前提下,应降低膜内部湿传递阻力;在膜组件（膜除湿器）方面,文献中获得的流动与传热传质基本准则数为膜组件的设计和优化提供了理论依据,另外,可通过增加翅片、冷却盘管或使用椭圆形中空纤维管来强化组件除湿性能。