叉流溶液除湿装置全热交换过程的解析解

除湿器是溶液除湿空调系统的重要组成部件。在已有叉流热质交换模型的基础上,通过合理简化给出了空气焓值、溶液等效焓值在除湿器内部的分布情况以及全热效率的解析解。解析解得到的焓值场分布情况与精确数值模型差分离散求解结果进行了比较,解析解得到的全热效率采用叉流除湿装置的实验结果进行验证,解析解与数值求解结果和实验结果很好的符合。该解析解可用于叉流除湿器的设计计算,也为叉流除湿器的场分布优化提供了条件。     

内冷却紧凑式叉流除湿器性能数值模拟与分析

该文提出了一种内冷却紧凑式叉流除湿器，对的该除湿器的除湿以及再生过程建立了热质交换的二维动态数学模型，并运用全隐式差分格式获得了该模型的数值解，对影响该类除湿器工作性能的多种因素及其作用结果进行了分析和对比，为除湿器结构的设计、工作状态点的选择提供了必要的理论依据。结果表明，本文提出的内冷却紧凑式叉流除湿器的性能较普通固定床式除湿器的性能有显著提高。     

内冷型液体除湿器数学模型及性能分析

提出了一种内冷型液体除湿器,并对该除湿器的除湿过程建立了热质交换的稳态数学模型.通过与实验结果的比较,发现数值计算结果与实验结果吻合较好,多数数据的偏差都在±10%以内.分析了各参数对除湿性能的影响,为除湿器的结构设计和性能分析提供了理论和应用依据.     

转轮除湿器简化模型数值模拟与性能分析

针对转轮除湿器建立了简洁实用的无量纲数学模型,分析了影响该设备除湿效果的无量纲因素;同时,通过对模型进行数值计算,以处理气流出口平均含湿量以及除湿效率为目标函数,定量分析了转轮结构、热质交换性能、运行设置、工作气流入口状态等几个重要方面的参数对除湿效果的影响,为转轮除湿器性能的优化提供必要的理论依据。     

逆流填料式液体除湿系统传热传质过程的分析解法及应用

通过对逆流填料式液体除湿系统传热传质过程数学模型的合理简化,推导出描述这一热质传递过程的常微分方程组的分析解,并与未简化数学模型的数值解作对比,二者具有良好的吻合性。所得分析解可用于分析填料高度上各参数的分布情况及各参量的变化对除湿性能的影响,并可用于除湿系统的设计校核计算等,具有较高的理论及应用价值。     

太阳能溶液除湿系统再生器的实验研究

结合工程实例进行了太阳能溶液除湿系统除湿溶液再生实验,研究了除湿溶液再生过程的热质交换特性,得到了不同溶液入口参数下再生器内部各测点温度,揭示了不同空气和溶液入口参数对出口溶液浓度的影响和填料对再生器热质交换的影响。文章可为太阳能溶液除湿系统再生器的设计提供依据。     

液体除湿系统的研究发展

液体除湿空调不仅可以对热负荷和湿负荷独立处理,而且不断循环的盐溶液还可以对空气起到很好的杀菌效果,这可以提高人们生活和工作的空气品质,避免由传统空调引起的温室效应。但是在溶液除湿和再生的过程中溶液表面的水蒸气压力与空气的水蒸气压力差不断减小,阻碍了除湿过程和再生过程的进行,所以为了得到更高的效率,需要探索新型的液体除湿装置。液体除湿系统主要由除湿器、再生器、循环溶液组成,其中再生器的性能直接影响到整个液体除湿系统的性能。简要介绍了传统液体除湿系统的再生器、除湿器、除湿溶液及新型液体除湿系统再生器的发展。     

内冷却紧凑式固体除湿器动态除湿性能研究

提出并研制一种新型粘贴干燥剂颗粒的内冷却紧凑式叉流固体除湿器,描述了这种除湿器的物理和数学模型,运用隐式差分格式数值求解该除湿器的偏微分控制方程组,模拟除湿器的动态除湿过程。通过实验得到了该除湿器的实际动态除湿性能,并将除湿器除湿性能的数值模拟结果与实验结果与进行了比较。实验和模拟计算结果均显示:该文研制的新型除湿器在高湿、低湿环境工况下都有良好的除湿性能;实验与计算的结果比较表明,本文所采用的内冷却紧凑式固体除湿器数学模型的数值解与实验结果吻合良好。该文研究结果对研制新型固体除湿(干燥)器具有很好的参考价值和应用价值。     

盐溶液与空气接触的除湿单元模块性能研究

在实验测量的基础上,分析了使用Celdek规整填料和溴化锂除湿溶液的叉流除湿模块的全热效率及除湿效率的影响因素,给出了两个效率的经验关联式,使用该经验关联式计算的全热效率和除湿效率的数值与实验结果的平均偏差分别为6.3%和6.0%。通过与文献中逆流除湿器的实验结果对比,该经验关联式的预测结果与实验结果很好的符合,也可用于预测逆流除湿器的性能。     

内冷型溶液除湿器的热质交换分析及流型比较研究

建立了分析传热传质的数学模型,并采用了文献中的实验数据进行验证,模型的计算值和文献中实验结果的偏差在±10%以内.藉此模型进行计算分析,得出内冷型除湿器的除湿量随着空气进口含湿量、溶液进口浓度、空气与溶液的传质单元数NTUa、溶液与冷水的传热单元数NTUw的增加而增大,随着冷水进口温度的增加而降低.针对文献中的空气与溶液逆流、冷水与溶液叉流的流型1和空气与溶液顺流、冷水与溶液逆流的流型2进行比较分析,得出相同情况下流型1的除湿性能总优于流型2,且两种流型的除湿量的差别随,NTUa的增加而增大.     

Model validation and case study on internally cooled/heated dehumidifier/regenerator of liquid desiccant systems

Traditional dehumidifiers and regenerators of liquid desiccant systems often use packed columns supporting adiabatic heat and mass transfer between air and liquid desiccant. As new-style equipment, internally-cooled dehumidifiers can improve dehumidification performance due to restraining temperature increase of the desiccant. Similar to internally-cooled dehumidifiers, an idea of internally heating is imitated to put forward internally-heated regenerators. The uniform mathematical model for an internally cooled dehumidifier and internally heated regenerator was presented and validated by comparison of computation results with experimental data in this study. The case study focused on the parameters distribution comparisons of the internally cooled/heated dehumidifier/regenerator with adiabatic ones and demonstrated coupled heat and mass transfer behavior. The results show that the internally-heated regenerator can produce higher regeneration efficiency than the adiabatic one to produce better energy efficiency and eliminate the dehumidification possibility which would happen in adiabatic regenerators. The internally-cooled dehumidifier can also provide better dehumidification performance comparing with the adiabatic one; however its benefit would be not as good as the internally-heated regenerator. In addition, effect of the width of the air channel on internally cooled/heated dehumidifier/regenerator was discussed and the results can help the optimal design of this kind of dehumidifiers and regenerators.     

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.     

Coupled heat and mass transfer characteristic in packed bed dehumidifier/regenerator using liquid desiccant

The dehumidifier and regenerator are two key components in liquid desiccant air conditioning systems. The heat transfer driving force and the mass transfer driving force influence each other, the air and desiccant outlet temperatures or humidity ratio may exceed the air and desiccant inlet parameters in the dehumidifier/regenerator. The uncoupled heat and mass transfer driving forces, enthalpy difference and relative humidity difference between the air and desiccant are derived based on the available heat and mass transfer model and validated by the experimental and numerical results. The air outlet parameter reachable region is composed of the air inlet isenthalpic line, the desiccant inlet equivalent relative humidity line and the linkage of the air and desiccant inlet statuses. Except the mass flow rate ratio and the heat and mass transfer coefficients, the air and desiccant inlet statuses and flow pattern have great effects on the dehumidifier/regenerator performance. The counter flow configuration expresses the best mass transfer performance in the dehumidifier and the hot desiccant driven regenerator, while the parallel flow configuration performs best in the hot air driven regenerator.     

Experimental Study on Effectiveness of Celdek Packed Liquid Desiccant Cooling System

Dehumidifier and regenerator are the most important components in a liquid desiccant cooling system. Present paper is focused on study the effect of inlet process parameters on the effectiveness of dehumidifier and regenerator of liquid desiccant cooling system. Experimental study is performed with varying inlet process parameters; mass flow rate of air, desiccant solution flow rate, inlet air temperature, inlet solution temperature, inlet specific humidity and concentration of desiccant solution. Celdek structured pads as packing material and calcium chloride as liquid desiccant is investigated first time using counter flow of the desiccant solution and air. It is concluded from the results that the effectiveness of dehumidifier increases with solution flow rate, inlet specific humidity while decreases with increasing mass flow rate of air, inlet temperature of air and desiccant, temperature and concentration of desiccant solution. The effectiveness of regenerator increases with increasing solution flow rate and inlet desiccant concentration and it decreases with increasing inlet air temperature, air flow rate and inlet solution temperature. Present paper adds to effect of inlet specific humidity, inlet temperature of the air and solution on the effectiveness of desiccant cooling system on the past research.     

Simplified analysis of coupled heat and mass transfer processes in packed bed liquid desiccant-air contact system

One-dimensional model is frequently used to describe the coupled heat and mass transfer processes in the packed bed liquid desiccant dehumidifier/regenerator. In this paper, within relatively narrow range of operating conditions which are usually encountered in practical dehumidification/regeneration processes, the linear approximation was made to find out the dependence of equilibrium humidity ratio on solution temperature. New parameters were defined and the original equations were rearranged to obtain two coupled ordinary differential equations. For the general cases with different values of Lewis factor, approximations of constant properties and coefficients were further made to render the coupled equations linear. Roots of the characteristic equation were determined algebraically and analytical solution to the linear coupled equations was obtained. Analytical expression for the tower efficiency was further developed based on the analytical solution. The way for obtaining the averaged overall heat and mass transfer coefficients from experimental data in a coupled heat and mass transfer manner was finally indicated. Coefficients obtained in this manner can be used in finite difference model to produce more accurate outlet conditions.     

Analytical solution of combined heat and mass transfer performance in a cross-flow packed bed liquid desiccant air dehumidifier

Heat and mass transfer between air and liquid desiccant in a cross-flow packed bed dehumidifier is investigated. Analytical solutions of air and desiccant parameters as well as enthalpy and moisture efficiencies are given in the present study, based on the analogy between the combined heat and mass transfer process in the cross-flow dehumidifier and the heat transfer process in the cross-flow heat exchanger. The results given by the analytical solution are compared with numerical solutions and experimental findings. Good agreement is shown between the analytical solutions and the numerical or experimental results. The analytical solutions can be used in the optimization of the cross-flow dehumidifier.     

Modeling and performance analysis of solar air pretreatment collector/regenerator using liquid desiccant

A solar liquid regenerator that embodies energy saving effect is a key part in solar liquid cooling air-conditioning system. Solar air pretreatment liquid collector/regenerator as a novel solar C/R (collector/regenerator) can achieve liquid regeneration in lower temperature, which is suitable to be employed in the high humidity area. The heat and mass transfer process was simulated in the novel liquid regenerator and the conclusions show that the increment of solution outlet concentration increases 70%, regeneration efficiency η_z augments 45.7% and storage capacity SC increases 44% as effective solution proportion ESP falls from 100% to 62%. For higher solution outlet concentration needed in the dehumidifier, both lower solution mass flow rate and higher solution inlet concentration all can be adopted in the novel C/R, in which the decrease of effective solution proportion ESP can increase the rate of evaporation G significantly. Along with the augment of air mass flow rate, the rate of evaporation G rises fast firstly and then falls slowly. The simulated results show that there is huge potential of improving and regulating solution regeneration performance by employing the novel C/R.     

Performance studies for an experimental solar open-cycle liquid desiccant air dehumidification system

A nominal 10.5-kW (3-ton) open-cycle liquid desiccant dehumidification system has been designed, installed, and successfully operated at the Solar Energy Applications Laboratory, Colorado State University. Packed bed units were used to dry the air in the dehumidifier and to concentrate the desiccant in the regenerator. Liquid distribution in the regenerator was studied for two systems: a gravity tray distributor, and a spray nozzle system. Higher capacities (40–50% increase) and lower pressure drop (30–40% reduction) for the air flow were observed with the spray system. Cooling capacities of 3.5–14.0 kW (1.0–4.0 refrigeration tons) were achieved for both the regenerator and dehumidifier. Functional relationships correlating the independent variables to the rate of vaporization in the regenerator and rate of condensation in the dehumidifier were obtained by statistical analysis of the experimental data. These studies thus provide data and correlations useful for design guidance and performance analysis of similar open-cycle liquid desiccant cooling systems, particularly for the liquid/vapor contact units.     

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.