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。     

金建祥:国内熔融盐储能技术已趋成熟

<正>中控德令哈10 MW塔式熔融盐太阳能热发电站项目是我国首个投入运行的以熔融盐为传热和储热介质的塔式项目,也是继西班牙Gemasolar、美国Crescent Dunes之后全球第3座商业化运行的熔融盐塔式电站。该电站是浙江中控在水工质塔式太阳能热发电站的基础上改造而来的,将水工质替换为主要通过双储罐结构,以二元硝酸盐作为吸热、储热介质,利用大规模定日镜场收集太阳能,将熔融盐加热并进行储存,     

液体除湿剂和空气热质传递过程的分析

以LiCl溶液为例,根据溶液温度和湿度将溶液表面边界层空气的状态表示在空气焓湿图上,分析了假想条件、理想条件和实际条件下的主流空气和边界层空气之间的热质传递过程,提出了衡量该过程的性能指标,简要介绍了改善该热质传递过程的途径。     

降低聚光太阳能热发电成本的途径

以系统年平均发电效率为引领,以发电工质温度和换热介质种类为主线,提出了降低聚光太阳能热发电成本的途径。     

建筑屋面太阳能被动蒸发冷却研究

提出利用多孔含湿材料太阳能被动蒸发冷却建筑屋面的新方法，建立了多孔含湿材料利用太阳能被动蒸发的热质耦合传递数学模型，通过理论分析，数值计算和实验测试，揭示了热过程规律，结果表明，利用太阳能被动蒸发多孔含湿材料水分降温方法是可行的。     

国内可再生能源文献信息

GN040401以空气为携热介质的开式太阳能吸收式制冷循环研究与分析.徐士鸣,刘渝宏.太阳能学报,2004,25(2):205-209.以空气为携热介质的开式太阳能吸收式制冷循环为研究对象,根据工作循环的特点给出了循环工作流程及计算方法,并对循环进行了详细的计算和分析,得出了循环COP值、制冷量、与湿空气出口处工作溶液与空气的水蒸气分压力差随热空气温度、环境温度和相对湿度之间的关系。通过研究发现,当热空气达到一定温度时,循环具有较好的稳定性。与闭式太阳能吸收式制冷循环相比,开式循环具有启动快、COP值高、系统简单、造价低等优点,特别适…     

太阳能辅助热泵干燥粮食的数值模拟研究

粮食的干燥过程实质上是多孔介质热湿耦合传递的过程。基于多孔介质热质传递理论,通过数值模拟的方法,针对利用太阳能辅助热泵干燥粮食时热风随时间变化的情况,采用综合温度和空气绝对湿度作为瞬态边界条件来对干燥过程中粮食内部温度和水分的变化进行模拟研究。模拟结果显示小麦水分在干燥150h后达到安全水分13.6%(干基),而实验结果显示小麦水分在干燥135h后达到安全水分13.6%(干基),二者对比相差不大,并且模拟温度与试验温度吻合较好。     

不同有机工质下的燃气分布式能源光热补偿供能系统研究

为了提高能源利用率,实现节能减排,以总能系统概念为基础,采用燃气和太阳能为能源,水蒸气与有机工质为工作介质,建立燃气分布式供能系统的热力模型和能效模型,对其热经济性和有机工质进行了计算与筛选。以国内某机场分布式能源站机组为例,基于太阳能的能源补充作用以及有机工质气化潜热小的特性,建立燃气分布式能源光热补偿供能系统,经热经济性计算与分析,结果表明:在100%、75%、50%制冷(制热)工况时、新模型在维持原机组总热耗的情况下,机组冷源损失减少,热经济性提高;经过对3种有机工质的筛选,R245FA是较适合于新模型的有机工质。     

多孔窗的开发与利用

介绍了一种以多孔介质为主体的新颖的空调装置－多孔窗，揭示了环境参数与多孔窗内部热质传递及其换热性能之间的内在联系，讨论了多孔窗性能的评价指标、优化设计参数、适宜工作范围及应用前景，从而为室内环境的降温提供了一种切实可行的方法．     

多层多孔介质层间界面处的热质耦合传递

为解决多层多孔介质层间界面处含湿量不连续而使含湿量梯度不能直接作为质传递驱动势的问题,该文在仍然以含湿量梯度为质驱动势的条件下,对界面处的质量和能量守恒方程进行适当改进,使对多层多孔介质热质耦合传递的模拟结果更符合实际,通过对已发表文献的实验结果进行验证,利用验证改进后的模拟方法对新建建筑多层多孔介质围护结构进行模拟,并与以界面处的平均体积含湿量梯度作为质驱动势对模拟结果进行对比。对比结果发现:利用改进后的模拟方法模拟的围护结构干燥速度小于后者的模拟结果,模拟结果也更接近实际情况。     

Effect of regeneration mode on the performance of liquid desiccant packed bed regenerator

The regenerator is one of the key components in liquid desiccant air-conditioning systems, in which desiccant is concentrated and can be reused in the system. The regeneration heat is supplied into the regenerator by either hot air or hot desiccant. The heat and mass transfer performances of these two regeneration modes are analyzed and compared in detail. In the hot air driven regenerator, the parallel-flow regenerator has the best mass transfer performance and the counter-flow performs poorest under the same conditions, because the heat transfer process is the governing process and the mass transfer performance depends on the promotion of the heat transfer to the mass transfer process. In the hot desiccant driven regenerator, counter-flow configuration has the best mass transfer performance and parallel-flow is the poorest at the same conditions, since mass transfer is the governing process. Regeneration heat should be chosen to heat the desiccant instead of the air in the packed bed regenerator, since the hot desiccant driven regenerator has apparent better mass transfer performance. The proposed regeneration mode and flow pattern will be helpful in the design and optimization of the regenerators.     

Theoretical study of tilted solar still as a regenerator for liquid desiccants

A closed type (tilted solar still) solar regenerator has been studied in application to regeneration with liquid desiccants. Essentially, it consists of a flat blackened, tilted surface with a transparent glazing as a covering. The absorbent solution which is to be regenerated trickles down as a thin film over the absorber and is heated by solar energy. The water vapor that evaporates from the liquid film is condensed on the under side of the glass cover and the solution leaving the regenerator becomes strong. A simple expression is derived, in this paper, to estimate the mass of water evaporated from the weak absorbent solution as a function of climatic conditions and initial conditions of the absorbent solution. A comparison is also made with a forced flow air circulation regenerator, and it was found that the closed type regenerator may be used for regeneration only in hot, humid climates.     

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.     

An experimental study of a forced flow solar collector/regenerator using liquid desiccant

One of the main components of a liquid desiccant cooling system is the regenerator. In a liquid desiccant air conditioner, outside air is dehumidified by liquid desiccant and cooled within the absorber. The diluted desiccant solution thus obtained has to be concentrated for reuse, by passing through the regenerator and the cycle is, consequently, repeated. The regenerator used in this application is a forced parallel flow type solar collector/regenerator. The regenerator has been designed and optimized and the prototype of the solar collector/regenerator has been built and tested. Calcium chloride has been used as the absorbent solution. The results of the tests conducted as a parametric analysis indicate that the air and solution mass flow-rates and the climatic conditions affect the regenerator performance. Furthermore, a comparison between the experimental data obtained and a previously developed model for a forced parallel flow solar collector/regenerator reveals that the experiments are in good agreement with the model predictions. Finally, it was concluded that the proposed solar collector/regenerator performs satisfactorily under the summer conditions of Adelaide, Australia.     

Diurnal response of an open roof solar regenerator system for absorption air-conditioning

This paper presents a time-dependent heat and mass transfer analysis of an open roof surface as a solar collector-regenerator system for absorption air-conditioning. The system consists of water evaporation from a lithium chloride solution (LiClH₂O) flowing on the roof of a building. The analysis takes into account the variation of the solution temperature-concentration and hence the water evaporation from the absorbent solution along the flow length of the regenerator and the periodic variation of the solar intensity and the ambient air temperature. The effects of operational parameters, viz. solution flow rate, regenerator length, humidity ratio and the inlet solution conditions, on the time dependence of the water evaporation have been investigated. It is ascertained that about 2.5–4.0 kg of water can be evaporated per unit solar regenerator area per day under typical operating conditions, and for every kg of water evaporated in the regenerator, 1 kg of water can be evaporated in the evaporator of the absorption cooling system. The overall average daily COP of the cooling system is found to be in the range 0.36–0.57 for a typical hot and dry climate, and hence, the system is more attractive for solar air-conditioning.     

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.     

Thermal characteristics of packed bed storage system

The thermal behaviour of a packed bed storage system charged with hot air is modelled using two partial differential equations representing the energy conservation in the air and solid phases constituting the bed. These two equations are coupled through the heat exchange process between the two phases. A fully implicit numerical scheme based on forward, upwind and central differencing for the time, first and second space derivatives, respectively, is used to solve the modelling equations. Marching technique is used for the air equation and a tri-diagonal matrix solver is employed to solve the solid equation. The solution yields the thermal structure of the bed, namely the air and solid temperature distribution inside the bed at any particular time, and the variation of total energy stored in the bed with time. The effect of bed length, solid diameter and void fraction on the thermal characteristics of the packed bed is studied. Further, the performance of the bed under variable inlet air temperature and mass flow rate is investigated.     

An analytical model to predict the thermal performance of a novel parallel flow packed bed solar air heater

A design of a parallel flow solar air heater with packed material in its upper channel and capable of providing a higher heat flux compared to the conventional non-porous bed double flow systems is presented. An analytical model describing the various temperatures and heat transfer characteristics of such a parallel flow packed bed solar air heater (PFPBSAH) has been developed and employed to study the effects of the mass flow rate and varying porosities of the packed material on its thermal performance. The model employs an iterative solution procedure to solve the governing energy balance equations describing the complex heat and mass exchanges involved. To validate the proposed analytical model, comparisons between theoretical and experimental results showed that good agreement is achieved with reasonable accuracy. Also, PFPBSAH is found to perform more efficiently than the conventional non-porous double flow solar air heaters with 10–20% increase in its thermal efficiency. Furthermore, the effect of the fraction of mass flow rate in the upper or lower flow channel of PFPBSAH device on its performance, has also investigated theoretically. The fraction of the mass flow rate in the respective channels of the PFPBSAH is shown to be dominant parameter in determining the effective thermal efficiency of the heater.     

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.     

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.