两段式塔式太阳能腔式吸热器设计及性能优化

发布时间：2019-03-08 18:57

【摘要】：随着国家能源结构调整步伐的推进,太阳能热发电由于其在节能减排、提升经济效益上巨大的潜力,已经被提上中国清洁能源重点发展的“日程”。从审批通过太阳能热发电项目到电价政策出台,可以预见,在未来的几年内,我国太阳能热发电产业将会出现“百家争鸣”式的发展。目前太阳能热发电主要以槽式为主,塔式太阳能热发电系统中又主要以熔盐为导热介质为主,对于以水/水蒸气为传热介质的吸热器,汽液两相分配的复杂性始终是阻碍其发展的一大障碍;同时,太阳能热发电的不连续性及热流密度分配不均等问题,也使得气液两相流分配不均更加严重。本文针对一种新型两段式塔式太阳能热发电的吸热器进行几何设计,建立了高斯热流密度分布条件下吸热器辐射和对流换热以及流动模型,确定了吸热器I和吸热器II受热面蛇形管管道布置方式和几何尺寸,获得了吸热器内部不同位置受热面的热流密度分布情况;结合气液两相传热和流动特点确定了吸热器典型管道内部工质温度、干度、压降和沿管道流程的壁温分布规律;整理出两段式太阳能腔式吸热器几何结构的系统化设计流程。对吸热器进行热力性能分析结果表明:两段式腔式吸热器能够有效减少预热蒸发吸热器的几何尺寸,提高平均辐射热负荷的同时降低吸热器的平均温度,有效提高吸热器的热效率;多管程蛇形管道布置可使出口参数分布更加均匀,避免受热严重不均等安全问题。为进一步改善联箱内部的水工质在加热过程中的两相流动特性,基于专利提出的笛形管均流器对联箱内两相流均匀分配的作用,本文采用CFD数值模拟,对加装笛形管前后联箱内汽液两相流的体积分数、速度场及分支管出口两相流的流量分配特性进行比较。结果表明:在两相流吸热器联箱中加装合适的笛形管均流器能对联箱内的汽液两相流进行再分配,明显改善联箱内部汽液分层现象和两相流分配不均匀问题。对太阳能热发电水工质吸热器设计有一定的指导意义。
[Abstract]:With the progress of national energy structure adjustment, solar thermal power generation has been put on the agenda of China's clean energy development because of its huge potential in energy saving and emission reduction and in promoting economic benefits. From the examination and approval of solar thermal power projects to the introduction of electricity price policy, it can be predicted that in the next few years, there will be a "hundred schools of thought"-style development in China's solar thermal power generation industry. At present, solar thermal power generation mainly consists of trough type, tower type solar power generation system is mainly composed of molten salt as heat conduction medium, and water / water vapor as heat transfer medium. The complexity of vapor-liquid two-phase distribution is always a major obstacle to its development. At the same time, the discontinuity of solar thermal power generation and the uneven distribution of heat flux make the distribution of gas-liquid two-phase flow more uneven. In this paper, the geometric design of a new type of two-stage tower solar energy heat exchanger is carried out, and the radiation, convection heat transfer and flow model of the absorber under the condition of Gao Si's heat flux distribution are established. The arrangement mode and geometric size of the snakelike pipes on the endothermic I and II heating surfaces are determined, and the heat flux distribution of the heating surfaces in different positions of the endoheater is obtained. Combined with the gas-liquid two-phase heat transfer and flow characteristics, the working fluid temperature, dryness, pressure drop and wall temperature distribution along the pipeline flow are determined, and the systematic design process of the geometry structure of the two-stage solar cavity absorber is arranged. The thermal performance analysis shows that the two-stage cavity absorber can effectively reduce the geometric size of the preheated evaporator, increase the average radiative heat load, and decrease the average temperature of the absorber, and the results show that the two-stage cavity heat absorber can effectively reduce the geometric size of the preheated evaporator. The heat efficiency of the heat absorber is improved effectively; The arrangement of multi-pipe serpentine pipe can make the distribution of outlet parameters more uniform and avoid the serious unbalance of heat. In order to further improve the two-phase flow characteristics of the hydraulic fluid in the header during the heating process, based on the effect of the patented pipe equalizer on the uniform distribution of the two-phase flow in the header, the numerical simulation of the two-phase flow in the header is carried out by using the CFD numerical simulation. The volume fraction, velocity field and flow distribution characteristics of the two-phase flow at the outlet of the branch pipe were compared before and after the flutes were installed in the header. The results show that it is possible to redistribute the vapor-liquid two-phase flow in the two-phase flow heater header by adding a suitable flute-tube equalizer, which can obviously improve the phenomenon of vapor-liquid stratification and the uneven distribution of the two-phase flow in the header. It has a certain guiding significance for the design of solar thermal hydro-hydraulic absorbers.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM615

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