【作者】 明廷臻；

【导师】 刘伟；

【作者基本信息】 华中科技大学 ， 工程热物理， 2007， 博士

【摘要】 论文基于太阳能热气流发电系统内流动与传热过程的热力学理论,对Helio-Aero-Gravity效应(简称为HAG效应)、结构参数对系统流动与传热特性的影响、带蓄热层的系统流动与传热特性以及负载条件下系统流动与传热特性进行了系统的分析与研究,取得如下一些有意义的研究成果。(1)对太阳能热气流发电系统不同区域的热力过程进行了分析,重新建立了系统的热力学循环,提出了能量利用度的概念,建立了系统的实际循环效率、理想循环效率以及系统不同部件的火用效率模型。太阳能热气流发电系统循环是一个Brayton循环。烟囱既具有提高系统效率的作用,同时又需要耗费大量的工质能量,这导致系统的循环效率远小于相同增压比的标准Brayton循环效率。此外,kW级小规模系统集热棚的火用效率较高而烟囱火用效率较低;而相比较而言,200MW大规模发电系统集热棚的火用效率显著减小而烟囱火用效率显著增大。(2)对太阳能热气流发电系统的HAG效应作了进一步分析。提出了一个更完善的模型以衡量太阳能热气流发电系统的性能,进一步考虑了太阳辐射和几何参数对系统相对压力、抽力、输出功率以及效率的影响。以西班牙模型为实例,数值模拟结果与理论分析模型预测结果具有良好的一致性。(3)对空载条件下太阳能热气流发电系统进行了流动与传热数值模拟,得到系统的温度场、速度场和压力场。结果表明:集热棚半径、烟囱高度、烟囱形状等几何参数均对系统内的传热与流动特性具有重要影响。之后,设计了一种螺旋集热式太阳能热气流发电系统并对其进行数值模拟,数值模拟结果表明:采用螺旋集热式太阳能热气流发电系统比常规的太阳能热气流发电系统更具有经济性和商业优势。(4)建立了包含蓄热层的太阳能热气流发电系统的流动与传热数学模型,并对包含蓄热层的太阳能热气流发电系统进行耦合数值模拟。计算结果表明:多孔蓄热层对太阳能热气流发电系统流动与传热特性的影响非常显著;多孔蓄热层具有热惯性,采用较高导热系数和热容量的多孔蓄热层对于提高系统发电连续性、调整系统发电峰谷差、提高系统能量利用度具有重要作用。(5)建立了包含透平、集热棚和烟囱的太阳能热气流发电系统的传热与流动数学模型,并对负载条件下不同规模的太阳能热气流发电系统进行传热与流动耦合数值模拟。计算表明:系统输出功率和能量转换效率随透平转速的变化存在一个极大值,系统流量和温度随透平转速的变化也比较显著。本论文提出的数值模拟方法为负载条件下太阳能热气流发电系统的进一步研究提供了有益的参考。(6)构建了小型太阳能热气流发电实验装置,测定了系统的温度随时间和空间的分布,测定了烟囱内的速度随时间的变化关系。实验结果表明集热棚内温度分布以及季节对系统的影响均与理论分析相一致。更多还原

【Abstract】 On the basis of thermodynamic theory for flow and heat transfer in the solar chimney power plant system, systematic investigations to the Helio-Aero-Gravity Effect (HAG Effect), effects of geometric size on the flow and heat transfer characteristics, effects of energy storage medium and turbine on the system performance are made in this dissertation, with some useful results obtained as follows:(1) An analysis of the thermodynamic processes in different regions of the solar chimney is carried out, in which the thermodynamic cycle of the system is rebuilt, the concept of energy utilization degree is put forward, and the mathematical models of practical and ideal efficiencies of the cycle and exergy efficiencies of different parts of the system are established. It is a Brayton cycle in the solar chimney power plant systems. High chimney is used to increase the efficiency of the system, but a great deal of heat energy will be lost when the working fluid passes through the chimney, which results in a much lower thermal efficiency of the system compared with that of the ideal Brayton cycle of the same pressure ratio. In addition, the kW-graded solar chimneys have a comparatively higher exergy efficiency of the collector and a lower one of the chimney, while the exergy efficiency of the collector decreases and that of the chimney increases significantly for the large scale systems with the output power about 200MW.(2) A further investigation to the Helio-Aero-Gravity Effect of the solar chimney power plant is producted. A more comprehensive model is advanced to evaluate the performance of the solar chimney power plant system, in which the effects of various parameters on the relative static pressure, driving force, power output and efficiency have been further investigated. Using the solar chimney prototype in Manzanares, Spain, as a practical example, the numerical studies are performed to explore the geometric modifications on the system performance, which show reasonable agreement with the analytical model.(3) Numerical simulation of the solar chimney power plant system with no load conditions is carried out. From the simulation results of the temperature, velocity and pressure distributions, we can find that the geometry parameters such as collector radius, chimney height and shape have significant effect on the flow and heat transfer characteristic of the solar chimney power plant systems. Furthermore, a new helix-collector solar chimney power plant system is designed, and the simulation results of this new model show that helix-collector solar chimney power plant system has economical and commercial advantages over the traditional solar chimney systems.(4) A set of more comprehensive mathematical models for the solar chimney power plant system including energy storage layer is established, and conjugate numerical simulations of the solar chimney power plant system with energy storage layer under no load conditions are carried out. The numerical results show that energy storage medium has thermal inertia and also has remarkable effects on the heat transfer and flow characteristic of the system, and that the adoption of energy storage medium with comparatively higher heat conductivity and heat capacity will be helpful to improve the continuity of power output, to modulate the difference of output power during the day and night, and to increase the energy utilization degree of the system.(5) A set of mathematical models to explore the performance of the solar chimney power plant systems coupled with turbine is also founded and conjugate numerical simulation on different sizes of the systems is carried out. Numerical simulation results show that, with the increase the turbine rotation speed, both output power and efficiency of the turbine have their maximum values, and that the mass flow rate of the system and temperature of the chimney outlet vary remarkably. The numerical simulation method put forward in this dissertation could give a useful reference to a further investigation of the solar chimney power plant systems coupled with turbines.(6) A minitype solar chimney power plant prototype has been built up, temperature distribution of the system with the time and space and the variation of chimney velocity with time have been measured. The experimental data show that temperature distribution inside the collector and the effects of season on the performance of the system are in great agreement with the theoretical analysis.更多还原