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主题 : 2009年全国优秀博士论文:溶液调湿式空气处理过程中热湿耦合传递特性分析
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楼主  发表于: 2009-10-10   

2009年全国优秀博士论文:溶液调湿式空气处理过程中热湿耦合传递特性分析

作者姓名:刘晓华 6 . +[ z  
  论文题目:溶液调湿式空气处理过程中热湿耦合传递特性分析 HI"!n$p  
  作者简介:刘晓华,女,1980年9月出生,2002年9月师从于清华大学江亿教授(中国工程院院士),于2007年7月获博士学位。 &rl]$Mtt  
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  中文摘要 ^DW#  
  溶液式空气处理装置是与常规空调完全不同的空气处理方式,其不是通过对空气进行降温到露点以下使水蒸气凝结从而除湿,而是通过液体吸湿剂与湿空气直接接触实现对空气的湿度处理过程。与传统的空气处理方式相比,采用溶液式空气处理方式,具有如下优越性:取消了冷凝水表面,消除了霉菌等生长所需的潮湿环境;既可以对空气除湿处理,又能实现冬季对于空气的加湿处理过程;可方便调节处理后的相对湿度,不再是常规冷凝除湿方式中接近100%相对湿度的出口空气参数;避免了常规空调系统冷凝除湿后温度过低还需再热带来的冷热抵消问题;可以充分利用低品位能源如太阳能和废热实现溶液再生,节省系统电耗。然而值得注意的是,尽管这种溶液式空气处理方式已出现近70年,但由于空气处理流程内在的问题,导致能源利用效率低于常规空调,因此并未得到广泛应用。本研究试图从溶液与空气之间最基础也是最重要的传热传质过程出发,深入剖析传热过程与传质过程的相互耦合影响,设法利用传热过程促进传质过程的进行,使溶液式空气处理方式的能源利用效率大幅度提高,从而替代目前空调系统中的空气处理方式,得到大幅降低能耗、精确控制室内温湿度和改善室内空气品质的效果。 ^7ea6G"  
论文的主要研究工作为: @e.OU(Bf  
  首先,对溶液与空气热质交换过程中传热、传质作用相互耦合影响的现象以及原因进行了全面的分析。给出了顺、逆、叉流不同流型下,溶液与空气绝热热质交换过程的数学模型,通过与溶液除湿/再生工况的大量实验数据的对比分析表明:Le数等于1时,求解结果与实验结果很好的吻合。溶液与空气之间的传热驱动力 、传质驱动力 相互耦合、影响,可能出现溶液与空气出口温度或(等效)含湿量超出二者进口参数所界定范围的情况。相互耦合影响的传热驱动力 与传质驱动力 ,可表示为相互独立的焓差驱动力 和相对湿度差驱动力 。 表征全热换热能力、 表征扩散到平衡的穷尽程度,溶液与空气出口参数在互相独立的两驱动力所界定的范围内变化。 %=NM_5a}]  
  其次,在相互独立的热质交换过程驱动力的基础上,提出了任意状态的溶液与空气热质交换过程所能达到的处理区域在:①空气进口等焓线;②溶液进口等浓度线(或等效相对湿度线);③两进口参数的连线所构成的三角形区域内。边界线①和②与相互独立的热质交换驱动力一致,边界线③的物理意义为:当溶液流量相对于空气流量非常大,热质交换过程对溶液状态的影响可以忽略不计时,空气处理过程的终状态点就位于两流体进口状态的连线上。溶液与空气热质交换过程的可及处理区域刻画出了任意状态的溶液与空气的热湿处理过程所能达到的处理状态,该可及处理区域适用于任意状态的溶液与空气的降温除湿、加热除湿、加热加湿、降温加湿等各种热湿交换过程的分析,从而为溶液与空气的热湿处理过程指明了方向。 !7IT~pO`  
  在可及处理区域的基础上,得到影响热质交换效果的核心因素除了众所熟知的溶液与空气的流动形式(顺流、逆流、叉流)、溶液与空气的流量比与传热传质系数外,溶液与空气的进口状态(溶液温度与浓度、空气温度与含湿量)也在很大程度上决定了除湿与再生过程的特性。以溶液的进口状态为中心,根据空气进口状态相对于进口溶液状态的位置,在焓湿图上划分成热质交换性能不同的A~D四个处理区域:A和D区为除湿区、B和C区为再生区;A和C区全热换热方向与传质方向相同、而B和D区相反。在相同条件下,位于A区的除湿(传质)效果远优于处在D区的冷却空气方式的除湿效果,位于C区的加热溶液方式的再生(传质)效果远优于处在B区的加热空气方式。相同条件下,位于A区的除湿过程和位于C区的再生过程中,逆流热质交换装置的传质性能最优,顺流装置最差,叉流装置介于二者之间;但对于B区的再生过程和D区的除湿过程,当溶液浓度变化较小(通常情况)时,顺流装置的传质性能最优,逆流装置最差,流型的优劣排序与A和C区有着明显的差异。 Z]7;u>2  
  而后,重点分析了溶液与空气的热湿耦合传递过程与单纯显热换热过程的异同,发现溶液与空气的全热交换过程(用焓表征)与单纯显热换热过程(用温度表征)有着相似的形式,可以应用显热换热过程的结果分析溶液与空气全热换热过程的特性。但由于在溶液与空气的热质交换过程中,传热过程与传质过程相互影响,目前普遍采用的借鉴传热学分析方法的对数平均湿差 法分析溶液与空气的传质过程,可能出现无意义或者计算结果与实际工况偏离较大的情况。本文提出采用对数平均焓差 法分析溶液与空气的热湿传递过程,计算结果与实际工况很好的吻合。 3PvZ_ !G  
  综合考虑溶液与空气热质交换装置的传热传质性能与压降损失,给出了处于不同分区内的单元热质交换装置的性能优化分析方法。溶液与空气热质交换过程所能达到的理想效率为热容量比m*、进口无量纲参数 与 的函数;可采用有效度 来衡量现有装置相对于理想装置的性能差异,从而为进一步提高其性能指明方向。原有叉流除湿/再生模块的尺寸为500×500×1200mm3,优化后的尺寸为600×350×830mm3,优化后的传热传质效果与压降损失与原有装置类似,但体积仅为原有装置的58%。 :/yr(V{  
  最后,在上述理论的指导下(譬如,热质交换过程宜位于A、C区,使传热过程尽可能促进传质过程等),以单元热质交换装置为基础构建出了溶液式全热回收装置、热泵驱动和余热驱动的多种形式的溶液调湿式空气处理设备,并在实际应用中取得了显著的节能效果。对于溶液式全热回收装置,在不增加体积投入的情况下,增加热回收装置的级数可以使得传热传质驱动力场分布更加均匀,是提高其效率的有效措施。由溶液式全热回收装置和热泵系统结合的溶液调湿新风机组,冬、夏测试工况下新风机组的性能系数COP均超过5。采用70~75℃热源驱动的溶液调湿新风机组的性能系数为1.2,远高于热水驱动的吸收式制冷机的性能系数,为夏季高效利用低品位热能提供了有效途径,对于我国城市能源结构有着重要意义。与国际上的研究成果相对比,热泵驱动的溶液调湿新风机组的性能系数提高了28%,余热驱动的溶液调湿新风机组的性能系数提高了约50%。溶液调湿新风机组处理后的干燥空气,可承担建筑所有的湿负荷从而有效地控制室内湿度,是温湿度独立控制空调系统的核心组成部件;而且可使用17℃左右的冷水(不再是常规空调系统中的7℃冷水)实现对室内温度的控制调节,为地下水、土壤等天然冷源的使用提供了条件。实际应用效果表明:当溶液再生热量可以免费获得时,温湿度独立控制空调系统的运行能耗仅为常规空调系统的50%左右;当再生热量不能免费获得时,则能比常规空调系统节省20%~30%的运行能耗。 5`{|[J_[  
  博士论文创新成果主要体现在以下几个方面: APHtJoS  
  在基础研究方面,1)分析了热湿耦合传递过程的可及性,提出了溶液与空气的热质交换过程终状态的可及范围;2)分析了不同入口条件下热湿传递过程的各自特点,据此提出了处理过程的区域划分方法,并给出了各区域的优化分析方法与热质交换过程所推荐的区域;3)揭示了溶液与空气的热质交换过程与单纯显热换热过程的异同,利用相似性直接获得溶液-空气热质交换体系的特征。以第一作者发表SCI检索文章8篇、EI检索文章6篇。 4! Oa4  
  在空气处理流程与工程应用方面,1)利用上述传热传质过程的结论,构建出溶液全热回收装置、热泵与余热驱动的多种形式的溶液除湿与再生装置的新处理流程,显著提高了溶液式空调设备的能源利用效率,并提出基于溶液调湿方式的温湿度独立控制空调系统形式;2)与课题组成员一起,研制出一系列溶液式空调样机并实现产品化,应用上述新处理流程的设备性能明显优于国外同类产品,已在北京奥林匹克森林公园艺术中心、上海建科院办公楼、深圳招商地产办公楼等二十余个建筑中应用,取得了显著的节能效果,约比常规空调系统节能30%。作者已获得授权的发明专利3项、实用新型专利4项(该实用新型专利同时申报了发明专利,其中3项发明专利在2008年7月至12月期间已授权,另有1项发明专利仍在审查过程中);以第一作者出版了《温湿度独立控制空调系统》的专著;溶液式空调方式的研究成果荣获2007年度国家技术发明奖二等奖(作者为第四完成人,学生中第一完成人)。 %vf2||a$BS  
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  关键词:溶液除湿,再生,温湿度独立控制,传热传质装置,空气调节 !OuTXa,I H  
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沙发  发表于: 2009-10-10   
Combined Heat and Mass Transfer Characteristic in Air Handling Process Using Liquid Desiccant h87L8qh9  
Liu Xiao-hua l# !@{ <  
ABSTRACT g6@NPQ  
Liquid desiccant air-conditioning system, in which air can be processed by directly contacting liquid desiccant, is one of the most efficient ways to deal with latent load (or moisture) in buildings and realizes a separately control of temperature and humidity. Comparing with conventional air handling process, the liquid desiccant air-conditioning system can dehumidify air without cooling down to its dew point. Meanwhile, counteraction cooling and heating can be avoided, which usually happened in conventional air handling process and led to huge energy waste. In addition, during the air handling process no condensation water separates out of the air in the liquid desiccant air-conditioning system, thus, avoid fungi thrives in moist environment of traditional air handling process. Not only being applied in dehumidification process in summer, the system can also realize humidification process in winter conditions efficiently. Furthermore, liquid desiccant system can be driven by low grade energy, such as solar energy and waste heat. ~P]HG;$?n  
The liquid desiccant system has already been applied for more than 70 years. However, due to unsolved problems existing in the air handling process which leads to a poor energy performance, the traditional liquid desiccant system was far from wide application. The study of this thesis focuses on the most elementary heat and mass transfer processes between air and liquid desiccant, especially dealing with the coupling impact of heat and mass transfer processes, which will contribute greatly to improve the energy performance, indoor air quality and promote liquid desiccant air-conditioning system in practices. \[IdR^<YM  
The main works of this dissertation are shown as following: (}~eD  
Firstly, the combined characteristic of heat and mass transfer processes between air and liquid desiccant is carefully investigated. Heat and mass transfer models at parallel-flow, counter-flow and cross-flow configurations are proposed and validated by large numbers of experimental results including dehumidification and regeneration processes. The numerical results show good agreement with the experimental results when Le number is assumed as one. The key physical parameters representing heat and mass transfer such as temperature and humidity ratio are investigated and one finds that these parameters of outlet air and desiccant can even exceed those of the inlet air and desiccant, due to the two driving forces of heat and mass transfer are combined. The combination of heat transfer driving force  and mass transfer driving force  can be presented as uncoupled driving forces of differential enthalpy  and differential relative humidity . Thus, differential enthalpy  presents the combined heat and mass transfer ability, which is the content of nearing equilibrium for total heat exchange. And differential relative humidity  presents the content that moisture near the equilibrium status. From a perspective of differential enthalpy  and differential relative humidity , the parameters of outlet air and desiccant are within those of inlet air and desiccant. PO%yWns30o  
Secondly, based on the uncoupled driving forces analysis, the reachable handling regions of heat and mass transfer between air and liquid desiccant are proposed. The parameters of outlet air are within a triangle area shown in the psychrometic chart, which is composed of the three boundary lines: (1) isenthalpic line of inlet air, (2) iso-concentration line (or iso-relative humidity line) of inlet desiccant, and (3) the linkage between the inlet status of air and that of desiccant. The boundary lines (1) and (2) are same to the uncoupled heat and mass transfer driving forces. There is a clear physical explanation of boundary line (3), that the parameters of outlet air will locate in the boundary line (3) when the flow rate of desiccant is essential large comparing with the flow rate of air, thus, the influence of heat and mass transfer on the variance of desiccant parameters can be neglected. The reachable handling region is universal applied that means it is suitable for any air and desiccant status, including cooling and dehumidification process, heating and dehumidification process, cooling and humidification process, heating and humidification process and so on. Thanks to this reachable handling region, the direction of liquid desiccant air-conditioning processes and the maximal /minimal reachable parameters of outlet can be easily determined. * 0&i'0>  
Thirdly, a zonal method is proposed for liquid desiccant air-conditioning processes analysis. Other than the well-known factors such as flow pattern, flow rate ratio, heat and mass transfer coefficients, mass transfer performance is also influenced significantly by inlet status of the air and that of the desiccant, including temperature and humidity ratio of the air, temperature and concentration of the desiccant. Four zones are divided in the psychrometic chart according to the relative inlet position of air to desiccant including two dehumidification zones, zone A and zone D, and two regeneration zones, zone B and zone C. In zones A and C, the direction of mass transfer is same to that of the combined heat and mass transfer, which is opposite in zones B and D. With the same operating conditions, the dehumidification performance in zone A is much higher than that in zone D, and the regeneration performance in zone C with hot liquid desiccant is much better than that in zone B with hot air as heating source. In zones A and C, counter-flow configuration leads to the best mass transfer performance; on the other hand, in zones B and D, parallel-flow configuration performs best when the desiccant concentration changes little (common condition). qh)!|B  
Fourthly, similarities and differences between the combined heat and mass transfer processes in dehumidifier/regenerator and the sensible heat transfer process in heat exchanger are analyzed. The total heat and mass transfer process (denoted as enthalpy “h”) in dehumidifier/regenerator is almost same to the sensible heat transfer process (denoted as temperature “t”) in heat exchanger. The solutions of the combined heat and mass transfer process in dehumidifier/regenerator can then be derived theoretically with that of sensible heat exchanger. One finds that the commonly used logarithmic mean differential moisture method may fail in prediction the mass transfer performance in dehumidifier/regenerator, or even meaningless in some situations, due to the influence of heat transfer on mass transfer process. New logarithmic mean differential enthalpy method is proposed which is applicable and adequate in prediction the coupled heat and mass transfer performances in air and liquid desiccant contacting processes. cT>z  
Fifthly, performance optimization in different zones is processed on single module considering of both heat and mass transfer performance and pressure drop. The ideal efficiency of air and liquid desiccant contacting process is a function of heat capacity ratio m*, air and desiccant inlet dimensionless parameters  and . The availability content  is then defined and used to evaluate the performance difference of current devices to the ideal condition. The module sizes before and after optimization are 0.5×0.5×1.2 m3 and 0.6×0.35×0.83 m3 respectively. Comparing to the original module size, the optimized packing volume decreases to 58% with almost same heat and mass transfer performance as well as the packing pressure drop. 2=Y_Qrhi  
In addition, new types of liquid desiccant air-conditioning devices are proposed based on the aforementioned studies and applied in practical projects. Thanks to the more uniformly heat and mass transfer driving forces, total heat recovery device based on the single module have better mass transfer performance with larger stages though the overall heat and mass transfer volume keeps constant. The COP of heat pump driven liquid desiccant outdoor air processor is over 5 both in summer for dehumidification and in winter for humidification. The COP of heat (70~75ºC) driven liquid desiccant outdoor air processor is 1.2, which provides an effectively mode to use the low grade heat in summer and benefits to the urban energy configuration. The performance of current heat pump driven and heat driven liquid desiccant outdoor air processor is 28% and 50% higher respectively, compared with other available liquid desiccant devices. Furthermore, liquid desiccant based temperature and humidity independent control air-conditioning (THIC) system is introduced, in which liquid desiccant system removes the entire latent load and other chilled water system (about 17ºC, instead of 7ºC in conventional air-conditioning system) removes the remained sensible load. The temperature requirement of chilled water makes the utilization of “free” cooling sources possible. The operating cost of the THIC system is only 50% of conventional air-conditioning system when regeneration heat of liquid desiccant is free, and the operating energy will also save 20%~30% even if regeneration heat can not be freely gained. {o5K?Pb  
The main innovative works are summarized as following: ];b!*Z  
Fundamental researches: 1) to propose the reachable handling region of air and liquid desiccant contacting process based on the decoupling analysis of heat and mass transfer driving forces; 2) to provide the handling zone dividing method only according to inlet parameters of air and desiccant; and 3) to analysis similarities and differences between the combined heat and mass transfer processes in dehumidifier/regenerator and the sensible heat transfer process in heat exchanger. The author has published 8 SCI-cited papers and 6 EI-cited papers. pZ_FVID  
Application researches: 1) to develop new liquid desiccant air-conditioning devices based on the above theory with higher energy-saving potential, including total heat recovery device, heat pump or heat driven liquid desiccant outdoor air processors, and provide liquid desiccant device based temperature and humidity independent control air-conditioning system; and 2) to develop a series prototypes with the cooperation of the research team members, and now the produces have already commercial available in the market and widely applied in Beijing, Tianjing, Shanghai and Shenzhen, and the performances are obviously higher than those of other available liquid desiccant products. The author has been authorized 7 patents, published 1 book as the first author, and awarded the Second National Prize for Technological Invention in 2007. :|m~<'g  
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Key words: liquid desiccant dehumidification, regeneration, independent temperature and humidity control, heat and mass transfer device, and air-conditioning
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