【作者】 韩崇巍；

【导师】 季杰；

【作者基本信息】 中国科学技术大学 ， 热能工程， 2009， 博士

【摘要】 近年来,我国城乡建筑的发展非常迅速。每年新建房屋的建筑面积高达16-19亿平方米。到2001年底,全国城乡的房屋建筑面积已超过360亿平方米。目前,全国建筑能耗已超过全国总能耗的四分之一以上,而且有持续上升的趋势。建筑能耗包括热水、采暖、空调、照明、家电等。其中,住宅和公共建筑的空调能耗在全部建筑能耗中占有很大的比重。随着常规能源的日益匮乏和环境问题的日益严峻,太阳能因其洁净、无污染、可再生等优点,日益受到人们的重视和青睐。在太阳能热利用领域,太阳能制冷空调具有对能量地利用与季节相匹配、对环境无破坏作用等优点,近几十年来得到了迅速发展。太阳能溴化锂吸收式制冷是目前最成熟的太阳能制冷技术,现已进入实用化示范阶段。目前,针对太阳能溴化锂吸收式制冷地研究开发主要集中在单效系统,这主要是因为单效系统对热源要求低（75-90℃）,系统通常选用价格便宜的平板型或真空管型太阳能集热器即可,系统成本相对较低,但系统的效率不高（COP 0.6-0.7）。本文对太阳能双效溴化锂吸收式制冷系统进行了理论研究。系统的太阳能集热部分采用具有反映灵敏、集热效率高和工作流体出口温度高等优点的抛物面槽太阳能聚焦集热器（PTC）,制冷机采用性能系数较高的热水型双效并联溴化锂吸收式制冷机。与太阳能单效溴化锂吸收式制冷系统相比,双效系统对热源的要求较高（120-160℃）,但对太阳能的利用效率更高（COP 1.2-1.5）,具有更好的节能效果。首先建立了PTC的一维、非稳态传热模型,对其沿轴线的光强分布进行了计算,对PTC在给定工况下的动态性能进行了数值模拟,并与远大空调有限公司的实验结果进行了比较,模拟结果与实验结果相差在4.61%以内,两者吻合较好,验证了模型的合理性。建立了热水型双效并联LiBr/H₂O吸收式制冷系统的稳态集中参数模型。通过数值模拟,研究了热源水进口温度、热源水流量、冷却水进口温度、冷却水流量、冷冻水出口温度、冷冻水流量、溶液分配比和溶液循环量等运转条件的变化对系统性能的影响,分析了运转条件变化容易引发的系统故障。计算结果表明:系统的制冷量和COP随运转条件的变化而变化;运转条件的变化需要控制在一定范围内,否则将引发溶液结晶、工作压力过高、冷剂水或冷冻水结冰等系统故障。以PTC和双效并联LiBr/H₂O吸收式制冷系统的模型为基础,对采用抛物面槽聚焦集热器（PTC）的太阳能双效LiBr/H₂O吸收式制冷系统的性能进行了数值模拟,研究了运行温度对系统总效率的影响,计算结果显示:PTC在高温工作条件下具有非常高的集热效率;运行温度为173.5℃时,系统总效率最高,达到0.8250;与采用复合抛物面聚焦集热器（CPC）和高效真空管集热器（ETC）相比,采用PTC的太阳能双效吸收式制冷系统具有最佳的系统性能;相同条件下,选用PTC时集热面积最小,但由于PTC的价格很高,导致系统成本很高。在合肥地区的气候条件下,对采用抛物面槽聚焦集热器（PTC）的太阳能双效LiBr/H₂O吸收式制冷系统进行了设计优化和经济性分析。系统由66.125m²PTC和16kW双效并联溴化锂吸收式制冷机组成,并增设了蓄热水箱和燃气辅助加热装置。研究了蓄热水箱容量及燃气辅助加热设定温度等对系统性能的影响。结果表明:蓄热水箱容量为0.6 m³、燃气辅助加热设定温度为158.0℃时,系统在制冷期内所消耗的燃气量最少;制冷期内系统获得太阳能113594.52MJ,太阳能保证率达0.5997;与只采用燃气的双效溴化锂吸收式制冷系统相比,太阳能双效制冷系统全年制冷期内可节省燃气4091.11m³;系统运行费用较低,但系统仍然是不经济的,这主要是由于PTC价格昂贵、初投资过大所致;当PTC价格低于$350.0/m²时,太阳能双效制冷系统才比只采用燃气的双效溴化锂吸收式制冷系统更经济。对双效并联溴化锂吸收式制冷系统双热源工作模式的热性能进行了理论研究,分析了低压发生器所消耗的热量及系统运转参数的变化对系统热性能的影响。计算结果显示:在双热源工作模式下,随着低压发生器所消耗热量的变化,为保证系统的正常运行,需要对溶液流量进行调节控制:随着低压发生器所消耗热量的增加,系统的节能效果更好,运行费用更低;溶液分配比的可调节范围随着运转条件的变化而变化。更多还原

【Abstract】 In recent years,the architecture of China has received great development.The area of the buildings in construction is 1600-1900 million square meters per year.By the end of 2001,the total area of the buildings of China has been more than 36000 million square meters.Now,more than a quarter of the total energy consumption of China is on building,and the trend keeps on increasing.As is known,the building energy consumption includes many aspects,such as hot water,heating,air conditioning,lighting,household appliances,etc.As a clean,non-polluting and renewable energy source,solar energy has received considerable attention due to the shortage of the normal fossil energy and the pollution of the environment.In the field of solar thermal utilization,solar cooling has received great development in recent decades since the availability of solar radiation matches very well with the varying cooling load demand and is friendly to environment.Among the solar cooling technologies,the solar LiBr/H₂O absorption cooling which has been in the stage of demonstration is ripest.Nevertheless,nearly all the studies on solar absorption cooling system focused on single-effect LiBr/H₂O systems.Single-effect LiBr/H₂O systems require hot water generator inlet temperatures in a low range of 75-90℃,so collectors of low price such as flat-plate pattern and evacuated tube collectors can be matched with them.Solar single-effect LiBr/H₂O systems has the advantage of low cost,but the energy efficiency is low （COP 0.6-0.7）.In this study,a solar double-effect LiBr/H₂O absorption cooling system is theoretical studied.The system mainly consists of parabolic trough collectors（PTC） and a double-effect LiBr/H₂O absorption chiller.PTC has the ability to obtain a high fluid temperature with high energy efficiency.Compared with single-effect chiller, double-effect chiller requires hot water generator inlet temperatures in a high range of 120-160℃.The energy efficiency of double-effect system is higher（COP 1.2-1.5）, which means a better energy-efficiency effect.An unsteady,one-dimensional heat transfer model of PTC is presented in this article.The distribution of the concentrated solar radiation along focal axis has been calculated.The thermal performance of the PTC is simulated,and the simulated results are compared with the experimental results.The comparison shows that the simulated and experimental results are in good agreement,and the difference between them is within 4.61%,which means the model set up is reasonable.A steady state concentrated parameter model of hot-water-driven double-effect parallel-flow LiBr/H₂O absorption refrigeration system is set up.The effect of the variation of operating conditions such as inlet temperature and mass flow rate of hot water,inlet temperature and mass flow rate of cooling water,outlet temperature and mass flow rate of cold water,solution distribution ratio and mass flow rate of solution on system performance is studied,and the possible faults caused by the variation of operating conditions are analyzed.Results show that the cooling capacity and the COP of the system vary with the variation of the operation conditions;system faults such as solution crystallization,overhigh working pressure, freezing of cooling water or chilled water will be caused if the variation of the operation conditions is out of range.Based on the theoretical study of the PTC and the double-effect parallel-flow LiBr/H₂O absorption refrigeration chiller,the system performance of the solar cooling system with PTC and a double-effect LiBr/H₂O absorption chiller is studied, and the influence of the operating temperature on the overall efficiency of the system is studied.Results show that the PTC has the ability to work at high temperature with high efficiency;the overall efficiency of the system achieves a maximum value of 0.8250 at operating temperature of 173.5℃;the system with PTC and a double-effect LiBr/H₂O absorption chiller has better system performance compared with the solar absorption cooling system with CPC and ETC;when PTC is used,its area is the least under the same design condition,but due to its high price,the cost of the system is still at a high level.A modelling and simulation is carried out for evaluating the system performance of a solar-assisted absorption cooling system under the climatic conditions of Hefei,China.The system consists of 66.125m² parabolic trough collectors（PTC）,a double-effect LiBr/H₂O absorption chiller of 16kW cooling capacity and a storage tank.The effects of gas-firing thermostat setting,storage tank size and collector area on the system performance are analyzed.The results show that an optimal performance is attained when the storage tank size is 0.6 m³ and gas-firing thermostat setting is 158.0℃.During the cooling season,the collector energy gain is 113594.52MJ,and the solar fraction reaches 0.5997.Though 4091.11m³ gases are saved per year compared with the gas-fired double-effect absorption cooling system,the system is not cost-effective due to the high initial cost. It is found that the solar-assisted absorption cooling system is marginally competitive with gas-fired absorption system when collector prices reach values less than $350.0/m².The thermal performance of double-effect parallel-flow LiBr/H₂O absorption refrigeration system under dual-heat mode of operation is theoretically studied,and the influence of variation of external heat capacity of low pressure generator and operation parameters on the performance of system is analyzed.Results show that under dual-heat mode of operation,the flux of solution should be adjusted with the variation of the external heat capacity of low pressure generator to ensure the normal operation of the system;an increase in external heat capacity of low pressure generator leads to a better effect of energy-saving and a lower operating cost;the adjustable range of solution distribution ratio changes with the variation of operating conditions.更多还原