冷凝内热源式液体空调再生器模拟研究

本文对以冷凝热为热源的LiCl溶液再生器进行仿真模拟,阐述了模型的建立及参数的选择。考虑利用冷凝热对除湿溶液进行再生,将管壁边界条件设为恒壁温,在恒壁温边界条件下,分别研究了溶液入口流速、温度及浓度、空气入口流速及温度与再生器出口参数的关系,得到空气出口温度随着空气入口温度、氯化锂溶液温度、浓度增加而增加;空气含湿量沿空气流动方向逐渐增加,并且随溶液入口温度、空气入口温度增加而增加;出口浓度随着入口氯化锂溶液浓度增加而增加等规律,当其他入口参数不变,溶液浓度达到34%时,溶液的再生量为11.3%。     

溶液除湿空调系统中叉流再生装置热质交换性能分析

再生器是溶液除湿空调系统中的重要传热传质部件。搭建了叉流再生器性能测试的实验台,并建立了叉流再生器中传热传质过程的数学模型。以溴化锂溶液为除湿剂,采用总换热量、全热效率描述再生器的热质交换总体效果,采用再生量、再生效率描述传质效果,实验测试了溶液和空气的进口参数对再生器性能的影响,并与逆流再生器的实验结果进行了比较。以实验得到的量纲一传质系数作为数学模型的输入条件,数值计算结果与73组实验数据吻合很好,全热效率和再生效率的偏差均集中在±15%以内。     

复合型太阳能溶液除湿空调的性能模拟

结合热湿地区的气候特点,设计了复合型太阳能溶液除湿空调系统,并通过数值模拟,分析了除湿器和再生器入口空气参数对系统性能的影响.结果表明,除湿器入口空气温、湿度从36℃和80%冷却减湿预处理到26℃和90%时,除湿器的体积可减小约63%,溶液循环量减小约58%;使用房间排风作为再生空气源,可明显提高溶液的再生效率和浓度,有效降低再生热源温度.     

除湿转轮效率研究

分析了目前除湿转轮效率定义存在的问题,提出了一种新的转轮效率定义.建立了一维非稳态氯化锂除湿转轮的数学模型,计算得到了不同再生空气温度、含湿量和不同处理空气温度、含湿量下的除湿转轮的除湿量及效率,并与文献实验结果进行对比,结果较为吻合.当转轮效率取0.85时,计算值与实验值的误差在±20%以内,且大部分值的误差都在±10%以内.     

基于高压雾化的溶液除湿性能实验研究

采用高压雾化将除湿液雾化成细小颗粒,可增大溶液除湿的接触面积,从而提高除湿效率。基于高压雾化的原理,搭建高压雾化溶液除湿系统实验台,研究空气量、溶液流量、空气状态对雾化除湿性能的影响。结果表明:高压雾化溶液除湿系统的除湿量随空气量、进口空气含湿量以及溶液流量的增加而增加;在进口空气温度为29.5℃,含湿量为21.44 g/kg,液气比为0.19的情况下,实验系统单位溶液除湿量可达15.78 g/kg;实验过程中,单位溶液的平均除湿量为10.39 g/kg;在相同除湿量下,雾化溶液除湿的单位溶液除湿量比传统填料式除湿器高2倍以上;拟合出除湿量的经验公式,可知实验值与测量值吻合得较好。     

液体除湿空调除湿性能影响分析

以液体除湿空调系统为实验对象,改变系统中除湿器入口空气及溶液的参数,得出空气出口温、湿度随之变化的状况.与理论模拟计算值比较,发现实验值和理论值有相同的变化趋势.由此得出各入口参数中,溶液的温度和流量的变化对空气出口温、湿度影响较大,空气的出口温度实验值偏小于理论值,空气的出口湿度实验值偏大于理论值.这将对液体除湿空调系统的性能分析和设计提供帮助.     

溶液除湿用泡沫陶瓷填料性能的实验研究

使用耐腐蚀的10PPI氧化铝(Al2O3)陶瓷泡沫作为溶液除湿填料并对其进行了实验研究.采用氯化锂的水溶液作为除湿剂.实验在人工环境舱中进行,研究了在溶液和空气处于逆流的情况下,进口空气流量、干球温度、含湿量以及进口溶液温度、浓度、流量对除湿量和除湿效率的影响.除湿效率和除湿量最高分别可以达到62.69％和0.819g/s.进口空气流量、含湿量,进口溶液流量、浓度的增加对除湿量增加起促进作用,但是进口空气干球温度、进口溶液温度的增加时除湿量是减少的.进口空气流量、干球温度以及进口溶液温度的逐渐增加时,除湿效率呈现下降趋势.进口溶液浓度对除湿效率的影响很小.利用实验结果拟合出了除湿效率和除湿量的表达式.     

平板降膜除湿场协同性分析

溶液除湿方式在节能领域有广阔的发展前景,对溶液除湿涉及的传热传质耦合过程进行研究可以完善相关理论知识。本文采用Fluent数值模拟方法,在渗透理论模型的基础上,从场协同的角度,利用协同角评价标准分析了不同工况下平板降膜溶液除湿过程。对不同入口速度、入口温度、入口浓度、入口含湿量进行了数值模拟。研究结果表明:选定工况范围内,浓度场和速度场的协同性随着入口溶液温度、入口空气流速的升高而减弱,随着入口空气含湿量、入口溶液浓度的增加而增强。该数值模拟为溶液除湿研究提供了新的研究角度。方差法分析得到各因素对协同性影响程度由大到小排序为溶液温度、溶液浓度、气流速度、空气含湿量。     

液体除湿再生性能的理论与实验差异性分析

以实际液体除湿空调系统为对象,进行了数值模拟和实验对比研究,结果表明,实验值和模拟值有相同的变化趋势;在诸多的入口参数中,溶液的温度、浓度以及空气含湿量对再生溶液浓度变化影响较大;溶液出口温度的实验值偏小于理论值,浓度变化的实验值偏大于理论值.重点分析了理论数据和实验数据产生差异的原因.     

金属填料型吸收式除湿器的除湿性能研究

通过理论和实验相结合的方式,对金属填料型吸收式除湿器的除湿性能进行了研究,分析和讨论了空气和溶液的进口状态参数对出口状态参数的影响.依据双膜理论建立了该除湿器的传热传质数学模型,并进行了理论研究.实验测试与模拟计算结果表明,溶液的状态参数对除湿器传热传质的影响较大.实验过程中除湿器运行稳定,具有应用的可行性.     

Performance analysis on the internally cooled dehumidifier using liquid desiccant

Dehumidifier is one of the most important components in liquid desiccant air-conditioning systems. Previous study shows that the internally cooled dehumidifier may have better mass transfer performance than the adiabatic unit. The effect of flow pattern, especially the flow direction of air to desiccant on the internally cooled dehumidifier performance is numerically analyzed in detail. The result shows that counter-flow configuration of air to desiccant has better dehumidification performance, and parallel-flow configuration performs the poorest with the same conditions, due to more uniform mass transfer driving force expressed in the counter-flow configuration. The decrease of the desiccant concentration is the main factor that influences the internally cooled dehumidifier's performance, while the increase of the desiccant temperature is the main performance restricting factor in adiabatic dehumidifier. Internally cooled dehumidifier has better mass transfer performance compared with adiabatic dehumidifier plus external heat exchanger.     

Experimental study on dehumidifier and regenerator of liquid desiccant cooling air conditioning system

A new type of air conditioning system, the liquid desiccant evaporation cooling air conditioning system (LDCS) is introduced in this paper. Desiccant evaporation cooling technology is environmental friendly and can be used to condition the indoor environment of buildings. Unlike conventional air conditioning systems, the system can be driven by low-grade heat sources such as solar energy and industrial waste heat with temperatures between 60 and 80 °C. In this paper, a LDCS, as well as a packed tower for the regenerator and dehumidifier is described. The effects of heating source temperature, air temperature and humidity, desiccant solution temperature and desiccant solution concentration on the rates of dehumidification and regeneration are discussed. Based on the experimental results, mass transfer coefficients of the regeneration process were experimentally obtained. The results showed that the mean mass transfer coefficient of the packing regenerator was 4 g/(m² s). In the experiments of dehumidification, it was found that there was maximal tower efficiency with the suitable inlet humidity of the indoor air. The effective curves of heating temperature on the outlet parameters of the regenerator were obtained. The relationships of regeneration mass transfer coefficient as a function of heating temperature and desiccant concentration are introduced.     

液体除湿器的数值模拟分析

建立了带填充物的液体除湿器的传热传质数值模型,并进行了相应的数值计算。计算结果表明,溶液入口温度和浓度对除湿性能有显著影响,进而影响液体除湿冷却空调的送风温度。     

溶液除湿过程热质交换规律分析

除湿器和再生器是溶液除湿系统的重要传热传质部件。建立了一个测试叉流除湿、再生模块性能的实验台,以溴化锂溶液为除湿剂,用除湿量、除湿效率和体积传质系数描述除湿效果,实验测试了溶液和被处理空气的进口参数对除湿器性能的影响。由实验数据得到的准则关联式,可供叉流除湿器设计参考使用。     

Modeling and simulation of desiccant wheel for air conditioning

This paper presents the modeling of a desiccant wheel used for dehumidifying the ventilation air of an air-conditioning system. The simulation of the combined heat and mass transfer processes that occur in a solid desiccant wheel is carried out with MATLAB Simulink. Using the numerical method, the performance of an adiabatic rotary dehumidifier is parametrically studied, and the optimal rotational speed is determined by examining the outlet adsorption-side humidity profiles. The solutions of the simulation at different conditions used in air dehumidifier have been investigated according to the previous published studies. The model is validated through comparison the simulated results with the published actual values of an experimental work. This method is useful to study and modelling of solid desiccant dehumidification and cooling system. The modeling solutions are used to develop simple correlations for the outlet air conditions of humidity and temperature of air through the wheel as a function of the physically measurable input variables. These correlations will be used to simulate the desiccant cooling cycle in an HVAC system in order to define the year round efficiency.     

Similarity of coupled heat and mass transfer between air–water and air–liquid desiccant direct-contact systems

Packed-bed heat and mass transfer devices are widely used in air-conditioning systems, such as cooling tower, evaporative cooler of air–water direct-contact devices, dehumidifier and regenerator of air–liquid desiccant direct-contact devices. Similarities of heat and mass transfer characteristics between air–water and air–liquid desiccant devices are considered and investigated in this paper. Same reachable handling region of outlet air can be obtained for both air–water and air–liquid desiccant devices, which is among three boundary lines, isenthalpic line of inlet air, iso-relative humidity line of inlet fluid (water or desiccant), and the connecting line of inlet statuses of air and fluid. Inlet conditions of air and fluid affect heat and mass transfer characteristics to some extent, so that a zonal method is proposed only according to the relative statuses of inlet air to inlet fluid. Four zones, dehumidification zones A, D and regeneration zones B, C, are divided for air-desiccant direct-contact devices. The first three zones A, B and C are divided for air–water direct-contact devices, with the same zonal properties as those of air-desiccant devices. In order to obtain better humidification performance, fluid should be heated (in zone C) rather than air (in zone B). And fluid should be cooled (in zone A) rather than air (in zone D) to obtain better dehumidification performance. Counter-flow pattern should be applied for best mass transfer performance in the same conditions within the recommended zone A or C, while parallel-flow pattern is the best in zone B or D.     

Simulation and experimental analysis of a fresh air-handling unit with liquid desiccant sensible and latent heat recovery

This article introduces a liquid desiccant fresh air processor. Its driving force is low-grade heat (heat obtained from 65 – 75°C hot water). Inside the processor, the air is dehumidified by the evaporative cooling energy of the indoor exhaust air. A four-stage structure is used to increase the efficiency of the combined sensible and latent heat recovery from the exhaust air. A mathematical model of the fresh air processor was set up using Simulink®. A liquid desiccant fresh air processor was constructed and tested for outside air conditions of 29.1 – 33.6°C, 13.7 – 16.7g/kg humidity ratio, and supply air conditions of 23.6 – 24.2°C, 7.4 – 8.6g/kg humidity ratio. The average measured COP _f was 1.6 (cold production divided by latent heat removed) for the range of conditions tested. The corresponding average COP _sys of the system including the regenerator was 1.3 (cold production divided by heat input). The detailed operating parameters of each part of the test unit were also measured. The test data was compared with the simulated performance. The characteristic coefficients (such as the volumetric mass transfer coefficient of the air-water evaporative cooling module, etc.) in the mathematical model were modified to calibrate the model output to the measured data. The calibrated simulation model was used to investigate the control strategy of the fresh air processor. The flow rate of the strong solution into the unit and the number of operation stages may be controlled separately or together to meet different indoor air requirements at different outdoor conditions. The hot water driven liquid desiccant air conditioning system was compared with a typical vapor compression system with an average COP of 4.5; the pump and fan power of the proposed system was 40% of the combined chiller, pump, and fan consumption. We achieved savings of over 30% of the power consumption compared with the traditional system under the designed outdoor air conditions.     

地源吸收式热泵夏季运行方式研究

针对现有的地源吸收式热泵在夏季运行工况时所出现的系统能耗高、空调房间易结露等问题,提出将集中热源驱动的新风溶液除湿机组和地埋管夏季免费供冷相结合,构成集中热源驱动的土壤源温湿度独立控制空调系统。选取北京地区某典型办公房间,以该系统为研究对象,建立各部分的数学模型,并模拟分析了新风量对系统性能的影响。结果表明:随着单人新风量的增加,地埋管水流量基本保持不变,除湿器入口溶液流量先是急剧下降,而后基本保持不变;再生器入口溶液温度逐渐升高,而再生器耗热量先是急剧下降,而后又逐渐上升,当单人新风量为30 m~3/(h·人)时,再生器耗热量达到最低;除湿器和再生器的湿传递效率均逐渐降低。     

溶液-湿空气热质交换过程的匹配研究

吸湿性溶液与空气的热质交换过程既有热量的交换又有质量的交换,提高该过程的可逆程度是提高溶液除湿空调系统性能的重要手段。在对溶液的性质进行合理简化的基础上,分析了溶液与空气的热质交换过程的流量比和过程需要吸收或释放的热量,得到在不同工况下,可逆过程所要求的流量比和应该补充或带走的热量。认为这一结论有助于溶液除湿空调流程的设计和相关参数的选取。