【作者】 刘研；

【导师】 高青；

【作者基本信息】 吉林大学 ， 动力机械及工程， 2010， 博士

【摘要】 道桥固体结构太阳能集热属固体平面太阳能集热的一种形式,其收集的能量可以通过跨季节地下储存直至冬季道路融雪化冰应用,形成夏集热蓄能冬融雪化冰的复合能源利用系统,将成为未来的新型道路交通和建筑领域应用的能源技术。道桥固体结构太阳能集热是夏集热蓄能冬融雪化冰系统的关键组成,因此本研究以新型道路冰雪热融技术为背景,通过理论分析、模拟计算与实验研究,探索其中所涉及的固体结构太阳能集热、地下蓄能和固体结构内管束循环流体流动等多阶段复杂时变过程的传热问题。在建立子模型分析基础上进行模型耦合,研究运行过程传热效能和能量利用,以及集热蓄能动态过程的控制和优化,为相关技术理论奠定基础,推动技术应用和科技进步。研究工作在国家自然科学基金项目(No.50776039)的支持下,针对道桥等固体结构构建夏季集热蓄能冬季融雪化冰复合系统,研究夏季太阳能集热单过程纯集热系统的传热特性和运行性能;分析夏季太阳能集热蓄能双过程中不同集热、蓄能控制方式的影响特点,探寻最佳控制方式;同时通过建立简化融雪化冰模型,耦合集热蓄能双过程模块,建立集热蓄能融雪化冰全过程仿真模型,系统分析不同气候条件下夏季集热过程收集能量和冬季融雪化冰过程支出能量的平衡性关系。其中,在针对夏季道桥路面太阳能集热过程研究中,建立了独立的数学模型和相应模块,以该模块应用为例分别研究道桥路面集热时循环流体流速、固体结构埋管管径、固体结构埋管管间距、固体结构集热表面状况、环境风速、环境温度以及浮云等因素的影响作用。结果表明,循环流体流速对集热量和流体温度作用明显,从集热蓄能综合角度考虑,其中低流速时蓄能效果更加显著应优先选择。埋管管径和埋管管间距增加对集热量和集热温度的影响具有相反效果,因此必须合理选择两者的关系,即在满足集热温度要求的情况下,合理选择布管参数以达到集热量获取最大化目的。吸收特性较好的集热表面有利于集热量和集热温度的增加,但集热表面温度也会因之大幅提升。环境风速和浮云的出现均会使集热量降低,对集热过程是一个不利因素。另外,同上述影响因素相比,环境温度变化对集热过程影响效果较小(环境温度上升1℃时单位面积集热量上升2W/m~2～3W/m~2),实际工程运行中可忽略其对集热系统的影响效果。通过开展道路应用模拟实验,进一步获知固体结构作为太阳能集热系统在夏季可以获得可观的热量,自然条件下集热能力为150W/m~2～250W/m~2,可以明显降低路面温度。同时道路等固体结构由于热容量较大,其集热温度和集热量变化时序均延迟于热源辐射强度的变化,表现出显著的集热滞后特性。实验还发现,固体结构内的埋管布置形式和流体流态参数对集热效果影响较大。随着循环流体流量的增大,集热效率增加,通常集热效率可达30%以上。随埋管管间距降低,集热效率明显提高,即表明集热面上的太阳辐射热量得到了充分吸收。实验研究范围内,管间距每降低10mm,集热效率平均升高5.5%。针对道路固体结构太阳能集热过程的主要影响因素开展实验研究,首次建立了固体结构热辐射集热室内实验系统,进一步研究单一影响因素对固体结构太阳能集热过程的影响效果,探索诸如辐射强度等众多客观因素的影响和作用。在定辐射强度和动态辐射强度实验中,重点研究了集热量、集热温差、集热效率和集热表面温度的影响特性。实验可知,随着热源辐射强度增加,集热系统的集热能力呈线性上升,但集热效率却呈下降趋势,而且道路等固体结构集热系统存在明显的热响应滞后性。另外增大环境风速可以降低路面集热温度,减小路面受热腐蚀,但循环流体集热温差和集热量却会随之下降,不利于集热和能量储存。同仿真计算结果相同,随循环流体流速增加,循环流体集热量和集热效率先增加而后降低,但集热温差逐渐降低。集热系统集热表面的吸热能力越强,集热效果越好,但表面温度也会上升,会降低路面强度,不利于路面的保护。在实验范围内,埋管管间距的增加使循环流体集热温差、集热量和集热效率降低。同蛇形直列盘管布置相比,椭圆盘管布置形式时循环流体集热温差和集热效率较高,利于集热蓄能,可见合理的埋管布置形式有利于太阳能吸收。为了探究夏季太阳能集热蓄能双过程的影响特性,基于Matlab/Simlink平台,又建立了太阳能瞬时辐射模块、固体结构集热器模块、蓄热水箱模块和地下换热器模块,以及利用模块组合构建出集热与地下蓄能复合系统,实现耦合分析。模拟计算集热蓄能双过程的传热特性,比较不同集热蓄能控制方法以寻找最优控制模式。通过组合系统研究发现,所提出的温差梯级流量蓄能控制模式在复合系统控制中更加有效,该方法通过控制开启、关闭蓄能运行和循环流体流量逐级变化,可避免路面平均温度过低地下热量回流散失的问题;同时避免地下换热器热源周边局部温升加大和路面集热能力下降的不良现象,保证路面集热蓄能系统综合用能效率,提高系统运行效能。而且控制温差不同集热蓄能双过程复合系统的运行性能也变化,本模拟计算中控制温差上升1℃地下温度下降约0.5℃。另外,太阳能集热控制方法中以温差开关控制为最优。研究中发现,虽然晴空辐射条件下太阳开关控制集热方法最优,但是实际气候条件瞬息万变,易造成系统运行状态变化,由于太阳开关控制没有产生与系统状态变化的联动性,因此对于太阳能固体结构集热器的控制应选择温差开关控制。通过建立简化的融雪化冰模块,研究工作对于夏季集热蓄能冬季融雪化冰全过程的传热效能和能量利用进行分析,研究发现集热能量不足或融雪化冰所需能量过大时,都会出现能量入不敷出现象,指出进一步探索集热蓄能和融雪化冰能量均衡,以及提升能源利用综合效率将是一项重要的进一步研究内容。综合研究表明,道路等固体结构太阳能集热是多阶段复杂时变传热过程。集热蓄能过程耦合、集热蓄能与融雪化冰过程耦合使研究面临更复杂的传热关联问题。本研究通过理论分析和模拟计算,结合实验研究,探索路面太阳能集热、地下蓄能,以及融雪化冰释热过程传热传质机理和特征规律,揭示集热蓄能融雪化冰各阶段的瞬态过程及其耦合控制策略,拓展和完善路面等固体结构集热蓄能融雪化冰过程的基础理论,可指导工程应用。更多还原

【Abstract】 Solar energy collection on pavement and bridge is of solar energy collection of solid structure. The collecting energy can be stored into underground and used to melt snow and deice in winter. Composite system of collecting and storing solar energy in summer and melting snow and deicing in the winter is constructed, which will be applied in road traffic and construction of new energy technology in the future.Solar collecting on the solid structure is a key component of composite system of collecting and storing solar energy in summer and melting snow and deicing in the winter. According to new hot melt snow technology, theoretical analysis, simulation and experiment is combined to study some complex heat transfer problems in the solar energy collecting, underground energy storage and circulating fluid. By coupling of sub-model, heat transfer performance, energy usage and control methods and optimization methods in the solar energy collecting and storage dynamic process are studied. The research is the basis of the relevant technical theory to promote the technology and scientific progress.Supported by the National Natural Science Foundation of China (No.50776039), a composite system is designed on the solid structure in this paper, which can collect solar energy and store energy in the underground in the summer, and melt away snow and deice in the winter. Heat transfer characteristics and operation performance of solar energy collecting system in the summer are studied. Influencing characteristics of different controlling methods in the process of solar energy collecting and energy storing are analyzed to work out the optimal controlling method. Simplized snow melting and deicing models are established and combined with solar energy collecting and energy storing process. Progress of solar energy collecting and storing and snow melting and deicing is simulated. Balance between energy collecting in the summer and energy using in the winter is analyzed accordingly.In the research of composite system of collecting and storing solar energy in summer and melting snow and deicing in the winter, an independent mathematic model and the corresponding module are established. Using heat collecting model, heat collecting characteristics and instantaneous influence effect of different influence factors, such as hydrolic fluid velocity, diameter and spacing of pipes buried in the solid structure, surface status, ambient wind velocity, ambient temperature and effect of cloud, are analyzed. The results show that with increasing of fluid velocity, heat collecting quantity per unit area increase, however, increasing extent will decrease. In the simulating range the optimal velocity is between 1m/s and 1.5m/s. Influence of pipe diameter and pipe spacing on heat collecting quantity and heat collecting temperature difference is reverse, so the relation should have an optimal range. Under reasonable heat collecting temperature, parameters of pipes should be chosen to make heat collecting quantity be maximized. Surface which has larger absorptance is in favor of heat collecting, but surface temperature will be higher. Wind and cloud reducing heat collecting quantity and are disadvantage factors. In addition, comparing with the above factors, effect of environmental temperature on the collector is smaller (when the ambient temperature rises 1℃, heat collecting quantity per unit area increases 2~3 W/m~2), thus its effects can be ignored in the actual construction of its operation.From the outdoor experimental system, it can be seen that large heat collecting quantity can be obtained by using solid structure as heat collecting slab. In the outdoor experiment the heat collecting quantity is about 150W/m~2~250W/m~2 under natural conditions. At the same time the temperature of road can be reduced. Due to the larger heat capacity of solid structures, the change of surface temperature and heat collecting quantity is lagged behind that of radiation intensity. In addition, pipe layout and fluid flowing state has a great impact. With the increasing of circulating fluid flow, collection efficiency increases. Collecting efficiency is usually up to 30%. With pipe spacing reducing, heat collecting efficiency improves significantly. As shown in the results, pipe spacing reduces with 10mm, heat collecting efficiency increases by an average 5.5%, which indicates that surface solar radiation energy has been fully absorbed.Since some factors are difficult to be controlled, the outdoor experiments the impacting effect of some factors are also possible crossed, and it is difficult to determine the impacting effect of a particular factor. Therefore, in order to study influence of single factor on the heat collecting process in the solid structure, and indoor thermal radiation simulation experiment bench is built to explore heat collecting performance and laws in the solid structure such as bridge and road.The experiment results show that with the increasing of heat radiation intensity, the heat collecting capacity in the system increases linearly, while heat collecting efficiency reduces. Solid structures such as road and bridge have obvious thermal response lag. In addition, with increasing of wind speed, heat surface temperature and corrosion reduce, while temperature difference per pipe length and heat collecting quantity per unit area will reduce, which is not conducive to energy storage. When circulating hot fluid flow velocity increases, temperature difference per pipe length, heat collecting quantity per unit area and heat collecting efficiency will increase, while the temperature of road will rise accordingly to reduce the strength of pavement and be not conducive to road protection. In the experimental range, with the increasing of the circulating pipe spacing, the temperature difference per pipe length, heat collecting quantity per unit area and heat collecting efficiency will reduce. Comparing with the snake coil arrangement, the temperature difference per pipe length, heat collecting quantity per unit area and heat collecting efficiency is higher in the ellipse coil arrangement, which is helpful for energy storage. Reasonable pipe layout is conducive to solar energy collecting.In order to explore influencing characteristics of solar energy collecting and storage (SECS) in summer, instantaneous solar radiation module, solid structure collector module, storage water tank module and underground heat exchanger module are designed based on Matlab/Simlink platform, to established solar heat collecting and underground energy storage model. Heat transfer characteristics of SECS is simulated and studied accordingly. Different controlling methods of SECS are compared to work out the optimal one. From the research, it is found that temperature control method is optimal, which is controlled by opening and closing storage process and adjusting the fluid flowrate. This method can not only avoid the average temperature of road to be too low to make heat of underground loss, but also avoid the temperature around the underground heat exchanger to be higher and reduce heat collecting ability of solid structure to ensure that the solid structure heat collecting and storage system and the system performance. When the controlling temperature difference changes, operating performance also changes. In the simulation cases, if the underground temperature rises 1℃, the decrement of controlling temperature difference will be about 0.5℃. In addition, the temperature difference switch control method in the solar collectors is an optimal one. Study also find that although under the conditions of clear sky solar switch control method is the best, the actual climatic conditions always changing, which will lead to operating system changing. Because there is no relation between the solar switch control and system changing, temperature difference switch control method should be chosen in the solar energy collector of solid structure.Finally, in order to study the operating performance of process of solar energy collecting and storing in the summer and snow melting and deicing in the winter. Using simplized snow melting and deicing models, combining with model of solar energy collecting and storing in the summer, heat transfer efficiency and energy usage of operating progress is studied. As shown in the results, when the collecting energy is too less or energy used in the melting snow and deicing is too much, so that energy does not make ends meet, underground temperature will be too low, and the system efficient will be too low.Comprehensive studies have shown that solar energy collection on the solid structures such as roads is a complicated heat transfer process. Coupling energy collecting with storage and couple energy storage and collecting wiht the process of melting snow and deice are more complex problems associated with heat transfer. In this study, theoretical analysis and simulation, combined with experimental studies are used to explore the mechanism and characteristics of heat and mass transfer. Thermal progress and control strategy in the energy underground storage and melting snow and deicing is revealed. The basic theory of solar energy collecting and underground storage and snow melting is developed and improved, which can be used to guide engineering applications.更多还原