一种新型溶液再生装置理论性能研究——太阳能空气预处理溶液集热/再生装置

提出一种适合我国南方夏季高湿天气的新型溶液再生装置--太阳能空气预处理集热/再生装置,它能使溶液除湿冷却空调系统的溶液在较低温度下实现再生.理论研究发现新型溶液再生器内空气和盐分存在一个匹配流量比ASMR及与之相对应的最大理论蓄能密度SCmax.理论计算发现在Tz=60℃、Cdil.sol=0.3条件下,当Ym由29g/Kg下降到14g/Kg时,匹配流量比ASMR值稳定在26～27范围内,而最大蓄能密度SCmax增大了50%.在定义有效溶液比(ESP)和有效蓄能密度(ESC)两个慨念的基础上,理论计算得出当ESP由100%下降到67%时,ESC不降反升;溶液出口浓度Cstr.sol由0.4升高到0.49,相对于浓度为0.3的稀溶液浓度升幅达90%.这些都充分说明了空气预处理再生装置具有极大提高溶液除湿冷却空调系统性能的潜力.     

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。     

液体除湿空调再生性能试验分析

液体除湿空调中除湿剂再生过程的效率和稳定决定整个系统运行效率和稳定性.对空气与除湿溶液质量流量之比、除湿溶液温度、除湿溶液的溶质浓度对除湿溶液再生系统性能的影响进行了探讨.     

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。     

太阳能空气预处理溶液再生装置稳态性能研究

通过数值模拟方法对太阳能空气预处理溶液再生装置进行研究发现,随着有效溶液比ESP的下降,再生器溶液出口浓度、再生效率ηz以及溶液蓄能密度SC均得到很大程度提高;在采用较小的溶液质量流量和较高再生器进口溶液浓度下,通过降低有效溶液比ESP均能明显提高蒸发率G;空气质量流量m.对再生性能的影响,除盲区和下降区外,有效溶液比ESP降低对再生性能提高显著.这些都说明了空气预处理再生装置具有极大提高溶液再生性能的潜力.     

太阳能液体除湿空调再生性能的实验分析

该文中再生器采用逆流式填料塔,并在填料塔设置中间加热器,采用排风进行再生.实验采用氯化锂作为除湿剂,重点分析了中间再热条件下,空气和溶液进口参数以及中间加热器和再生性能的关系,并讨论了再热对单位再生能耗的影响.     

太阳能平板降膜型再生器的模拟和实验研究

在对液体再生机理研究的基础上,针对对流和辐射传热边界条件,建立了太阳能平板集热型再生器中逆流降膜再生过程的数学模型,并通过实验方法对该模型进行验证,实验采用CaCl2水溶液作为除湿剂,分析了各种进口参数对再生效果的影响.结果表明:模拟结果与实验数据能够较好地吻合;太阳辐射强度、空气温度、空气含湿量和溶液浓度等均对再生过程有不同程度的影响.     

液体除湿空调系统中除湿过程的模拟和实验研究

在对液体除湿机理研究的基础上,针对对流传热边界条件,建立了内冷型竖直板逆流降膜除湿过程的数学模型,并通过实验方法对该模型进行验证,实验采用CaCl2水溶液作为除湿剂,分析了各种进口参数对除湿效果的影响。结果表明:该数学模型能够较好地解释竖直板降膜除湿过程;空气和溶液的流量、温度,空气的含湿量,溶液的浓度等均对除湿过程有不同程度的影响。     

中国公寓建筑热湿独立处理空调系统全年能耗仿真及对比分析

热湿独立处理空调系统是一种新兴的可以将空气温度和湿度分开处理的系统,其强除湿性及节能性对建筑节能具有重要意义。本文在建筑能耗仿真软件中建立了热湿独立处理空调系统,对其能耗进行了全年8 760 h的仿真并与分体式空调系统进行了对比。结果显示：在长江流域以南及沿海地区的热湿气候下溶液除湿空调系统最节能,在长江流域以北内陆地区的寒冷干燥气候下使用分体式空调更加节能,冷凝除湿再热过程是造成热湿气候下分体式空调能耗高的原因。     

基于溶液除湿的风冷热泵系统性能分析

为了克服利用冷却除湿的风冷热泵空调系统机器露点过低、需要再冷和过热、难以适应显热潜热比例的变化、不能蓄能等缺点,提出基于集热再生器溶液除湿的热泵空调系统。通过济南某工程实例研究表明,与冷却除湿空调系统相比较耗电量减少12.3%,利用太阳能加热溶液除湿具有降低空调除湿能耗、利用可再生能源、减少高品位能源消耗等优势。证明太阳能溶液除湿在空调系统中是处理潜热负荷的理想选择,具有较好的节能性。     

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.     

Evaporation rate of a novel tilted solar liquid desiccant regeneration system

The regeneration system represents a vital part of any desiccant air conditioning system. The need of a solar assisted desiccant regeneration system is more important today. In this paper, an experimental study of a novel regeneration system modified from solar tilted still is carried out. A corrugated blackened surface is used to heat the desiccant and an air flow is used to regenerate calcium chloride solution. The effect of the liquid to air flow rate ratio; the desiccant temperature; the desiccant concentration and the inlet air humidity ratio on the evaporation rate has been studied experimentally. A wide range of liquid to air flow rate ratios are employed. The optimum value of the liquid to air flow rate ratio for higher evaporation rate is reported.     

Mathematical modelling and experimental investigation of the hybrid desiccant cooling system

In this paper, an experimental study has been conducted on the hybrid desiccant cooling system by removing the latent heat and sensible heat of air separately by mixing it with the desiccant solution in a counter flow manner. This makes air totally dry and thus saves the energy to cool the air in the refrigeration system. The desiccant chosen here is the aqueous solution of calcium chloride. The packed bed inside the absorber as well as the regenerator consists of a polypropylene cascade ring for the efficient mixing of air and desiccant solution. The effects of various parameters such as desiccant inlet temperature, air inlet temperature, mass flow rate of air and desiccant solution have been studied to investigate the performance of the system. Comparing the results with previous studies, a fair agreement has been reported.     

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.     

Effectiveness of heat and mass transfer in packed beds of liquid desiccant system

A liquid desiccant system (using CaCl₂) is presented for air dehumidification using solar energy or any other low grade energy to power the system. The system utilizes two packed beds of counterflow between an air stream and a solution of liquid desiccant for the processes of air dehumidification and solution regeneration. To simplify the prediction of the performance of the system an effectiveness of heat transfer and an effectiveness of mass transfer in the packed beds are defined. A finite difference model is developed to model the heat and mass transfer in packed beds during the air dehumidification mode and the solution regeneration mode. This finite difference model is used to calculate the effectiveness of heat and mass transfer in the packed beds at various bed heights, various air and solution flow rates, various inlet temperatures of air and solution to the bed, and various concentrations of CaCl₂ solution at the bed entrance. Charts of the effectiveness of heat and mass transfer are presented in a convenient form. A designer of a liquid desiccant system may use the charts in predicting the performance of these systems without having to use the finite difference model for this purpose.     

Quick performance prediction of liquid desiccant regeneration in a packed bed

The major energy requirement associated with any liquid desiccant-based systems is the low-grade energy for desiccant regeneration. This paper presents the results from a simplified model of a packed bed regeneration process in which the desiccant solution is heated in any of the two ways. With method A, the desiccant solution is heated in a heat exchanger with a fluid (water) heated by any low-grade thermal energy such as solar energy or waste heat sources. While in method B, the desiccant solution is heated by a conventional energy source such as a line heater. A closed form solution is obtained for both methods of heating through two dimensionless performance parameters to estimate the water evaporation rate from the weak desiccant solution to the scavenging air stream in terms of known operating parameters. Good agreement is shown to exist between the predictions from the simplified model and the experimental findings available in the literature. The influences of the heating fluid (water) inlet temperature and the effectiveness of the heating fluid-to-desiccant heat exchanger on the performance of the regenerator are studied for method A whereas the effects of energy input on the evaporation rate of water with the scavenging air flow rate are investigated for method B and the results are reported in this paper.     

A new method for determining coupled heat and mass transfer coefficients between air and liquid desiccant

This paper presented the characteristic of liquid desiccant dehumidification based on NTU–Le model. The results showed that the Lewis number Le had little effect on air outlet humidity ratio during desiccant solution dehumidification process. A new method called h_D–Le separative evaluation method was developed for determining coupled heat and mass transfer coefficients between air and liquid desiccant, through which the heat and mass transfer coefficients between air and liquid desiccant were calculated to obtain from experimental inlet and outlet parameters of air and desiccant solution. The effects of the air volume flow rate, temperature, humidity ratio and the solution concentration, temperature on the Lewis number, heat and mass transfer coefficient were analyzed according to experimental data and the h_D–Le separative evaluation method. Based on the computation results, it was concluded that the Lewis number greatly depended on the operation parameters and conditions of the air and desiccant. In addition, the correlations of the heat and mass transfer coefficients were developed. The additional 74 groups of experiments validated the developed correlations by comparison of air/solution parameters change with the calculation data.     

An analytical model for heat and mass transfer processes in internally cooled or heated liquid desiccant–air contact units

Internally cooled or heated liquid desiccant–air contact units can be used for effective air dehumidification or desiccant regeneration, respectively. One-dimensional differential equations were utilized in the present study to describe the heat and mass transfer processes with parallel/counterflow configurations. The effects of solution film heat and mass transfer resistances, the variations of solution mass flow rate, non-unity values of Lewis factor and incomplete surface wetting conditions were all considered in the differential model. On considering the relatively narrow ranges of operating conditions in a specified application, the equilibrium humidity ratio of desiccant solution was assumed to be a linear function of its temperature and concentration. Constant approximations of some properties and coefficients were further made to render the coupled equations linear. The differential equations were rearranged and an analytical solution was developed for newly defined parameters. For four possible flow arrangements and three types of commonly used liquid desiccant solutions, results of analytical solutions were compared with those of numerical integrations over a wide range of operating conditions, and the agreement was found to be quite satisfactory. Further, the heat and mass transfer performances were analyzed and some guidance to improve the unit design was provided.     

The effect of inlet parameters on the performance of packed tower-regenerator

An investigation on the operation of packed tower for the regeneration of liquid desiccant is presented. A theoretical model demonstrating the effect of the system parameters is described. The experimental results are plotted to illustrate the effect of air and liquid parameters on the output variables. The regeneration process is shown to be highly dependent on the air inlet conditions, namely, temperature, humidity and flow rate. Also, the effects of the liquid temperature, concentration and flow rate is discussed. Data obtained were correlated to estimate the rate of water evaporation (regeneration rate) from values of variables that influence the rate of mass transfer in the column.     

Performance study on a structured packed liquid desiccant regenerator

The solution carryover in traditional desiccant regeneration towers is of serious concern in real applications especially when using triethylene glycol (TEG) as a desiccant. In this study, the cellulose rigid media pads are used as the structured packing. The packing arrangements have provided minimum carryover of TEG. A performance study of the simultaneous heat and mass transfer between air and desiccant in a structured packed-stripping tower is conducted. Through the study of the regenerator, important design variables are defined and the regenerator performance is compared with the previous studies. The effects of air and liquid flow rates, air humidity, desiccant temperature and desiccant concentration have been reported on the evaporation rate and humidity effectiveness of the column. It is found that high liquid flow rates do not have a significant effect on the performance variables.