塔式太阳能热发电吸热器蒸发段沸腾传热的数值模拟

发布时间：2018-01-12 04:25

本文关键词：塔式太阳能热发电吸热器蒸发段沸腾传热的数值模拟　出处：《华北电力大学》2015年硕士论文　论文类型：学位论文

【摘要】：近年来,随着能源需求的剧烈增长,太阳能热发电技术正成为世界范围内可再生能源领域的热点。太阳能吸热器是太阳能热发电站中光-热转换的核心部件,其性能直接影响整个电站的正常运行。吸热管面向镜场的半圆周受热,且热流密度沿轴向不断变化,背向镜场的半圆周绝热；同时集热管内水-蒸汽工质的沸腾流动换热尤为复杂,因此研究其受热特性具有重要意义。本文基于ANSYS FLUENT平台,数值计算三维、非稳态的汽液两相流动。模拟分析结果呈现了吸热管管内的汽液两相流动特性,描述了吸热管轴向方向汽液两相流的流型演变和速度分布。另一方面,结果揭示了吸热管管内工质和管壁的热特性。沿轴向方向,工质不断受热,温度逐渐升高至饱和温度373 K。吸热管管壁温度在轴向和周向方向温度分布极不均匀,与管壁受热侧表面能流密度分布有很大的相关性。最大壁温和管道横截面最大温差均出现在Z=1000mm的吸热管管道截面。吸热管轴向的Nu数与管内汽液两相流流型密切相关,在泡状流阶段达到最大值。进一步,文章分析了吸热管三个方向(轴向、轴向、径向)的温度梯度变化和最大绝对温度梯度。该文分析结果有助于深入了解塔式电站吸热器吸热管的整体性能。塔式太阳能热发电站定日镜场通常采用多点聚焦策略来降低吸热器表面辐射能流的不均匀性,防止发生过热故障。本文以塔式电站柱式吸热器单根吸热管为研究对象,采用具有多个极大值的高斯函数来描述多点聚焦时吸热管表面具有多个能流集中点的辐射能流分布,数值模拟分析吸热管的热参数特性。结果显示：聚焦点个数一定时,存在最优的聚焦点位置,使得吸热管表面辐射能流不均匀性最低。同时随着聚焦点个数增加,吸热管表面辐射能流更加均匀,最大壁温减小,而轴向最大绝对温度梯度增大。因此对于多点聚焦,应综合考虑吸热管的热参数,选择最优化的聚焦点个数和聚焦点位置。
[Abstract]:In recent years, with the rapid growth of energy demand, solar thermal power generation technology is becoming a worldwide hot spot in the field of renewable energy. Solar energy absorber is the core component of photothermal conversion in solar thermal power plants. Its performance directly affects the normal operation of the whole power station. The heat flux of the endothermic tube is heated on the semi-circular circle of the mirror field, and the heat flux is constantly changing along the axial direction, and the semi-circular circumferential adiabatic heat of the backmirror field is obtained. At the same time, the boiling heat transfer of water-steam working fluid in the collector pipe is very complicated, so it is of great significance to study its heating characteristics. Based on the ANSYS FLUENT platform, the three-dimensional numerical calculation is carried out in this paper. The simulation results show the characteristics of vapor-liquid two-phase flow in an endothermic pipe, and describe the evolution and velocity distribution of the gas-liquid two-phase flow in the axial direction of an endothermic tube. The results reveal the thermal characteristics of the working fluid and the tube wall in the endothermic pipe, and the working fluid is continuously heated along the axial direction. The temperature gradually rises to the saturation temperature 373 K. the temperature distribution of the endothermic tube wall in the axial and circumferential directions is extremely uneven. The maximum temperature difference of the cross section of the maximum wall and pipe appears in the section of the endothermic pipe with Z1000 mm. The number of Nu in the axial direction of the endothermic pipe and the steam in the tube are closely related to the distribution of the energy flow density on the surface of the heated side of the tube wall. The flow pattern of liquid two-phase flow is closely related. In the bubbly flow stage, the maximum value is reached. Further, the three directions (axial, axial) of the endothermic tube are analyzed. Radial). The results of this paper are helpful to understand the whole performance of the absorber tube of tower type power station. The multi-point focusing strategy is usually used in the helioscope field of tower solar thermal power station. Reduce the non-uniformity of radiation energy flow on the surface of heat absorber. In this paper, the single tube of column absorber of tower power station is taken as the research object. The Gao Si function with multiple maximums is used to describe the radiation energy flow distribution on the surface of endothermic tube with multiple energy flow concentration points. The numerical simulation results show that there is an optimal focal point position when the number of focal points is fixed. At the same time, with the increase of the number of focal points, the radiation energy flow on the surface of the endothermic pipe is more uniform, and the maximum wall temperature decreases. The axial maximum absolute temperature gradient is increased. Therefore, the heat parameters of endothermic pipe should be considered synthetically, and the optimum number of focal points and the location of focal point should be selected for multi-point focusing.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM615

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