考虑压降下有机朗肯循环的性能分析及蒸发器优化设计

发布时间：2018-03-13 22:27

本文选题：有机朗肯循环　切入点：流动压降　出处：《湘潭大学》2017年硕士论文　论文类型：学位论文

【摘要】：有机朗肯循环(Organic Rankine Cycle,简称ORC)发电技术是一种高效低品位余热回收技术,具有结构简单、热效率高,蒸发压力相对较低等优点。本文针对ORC发电技术,在考虑流动压降下分析运行参数对系统整体性能的影响,开展蒸发器运行参数和结构参数的多目标优化,该研究对ORC发电技术的工业应用有一定的指导作用。具体内容和结论如下:1)建立ORC系统流动压降计算模型与系统热力分析模型,根据给定的初始参数对系统蒸发器和冷凝器进行设计,得到翅片管式蒸发器的管长为159.6m、换热面积为46.26m~2,板式冷凝器的板片数为57、换热面积为27.58m~2;依据ORC系统工质筛选原则,选取R245fa、R123、R600a、R141b、R134a和R236ea等六种常用循环工质。在此基础上,利用文献结果验证了模型的可靠性。2)研究运行参数(蒸发压力、过热度、节点温差)和热源温度对流动压降的影响规律,并以净输出功、热效率、?效率、热回收率、不可逆损失为评价指标,对比分析流动压降对ORC系统性能的影响规律。结果表明:ORC系统的流动压降主要由蒸发器压降组成,且蒸发压力是影响系统压降的主要因素。考虑流动压降下,蒸发压力低于0.8MPa会导致系统各性能指标的降幅增大。对于干工质,节点温差与过热度对流动压降的影响较小,不同节点温差下流动压降对系统性能的影响小于10%;流动压降随着热源温度的升高而增大。此外,工质是影响系统流动压降与系统性能的重要因素,几种工质中,R141b和R245fa为最佳工质。3)以ORC系统的流动压降、净输出功、热效率和热回收率为优化目标,以蒸发器的热力参数(蒸发压力、过热度、节点温差)、蒸发器结构参数(换热管的管长、单排管子数、翅片高度、翅片厚度和翅片间距)为设计变量,采用模拟退火优化算法对ORC系统蒸发器进行优化设计,分析蒸发器热力参数和结构参数对ORC系统性能的影响规律。结果表明:系统各性能指标之间存在博弈与对立现象,蒸发器热力参数中蒸发压力对目标函数值的影响最大,优化条件下R245fa的最佳蒸发压力为2.5MPa;蒸发器结构参数中,翅片结构是影响系统热力性能的重要因素,而换热管布置方式对系统热力性能的影响基本可以忽略。对于R245fa,优化后的翅片结构参数为翅片高度34mm、翅片厚度7.3mm、翅片间距3.5mm。
[Abstract]:Organic Rankine cycle (ORC) power generation technology is an efficient and low grade waste heat recovery technology, which has the advantages of simple structure, high thermal efficiency and relatively low evaporation pressure. Considering the flow pressure drop, the influence of operation parameters on the overall performance of the system is analyzed, and the multi-objective optimization of evaporator operating parameters and structural parameters is carried out. The research can be used to guide the industrial application of ORC power generation technology. The specific contents and conclusions are as follows: 1) the flow pressure drop calculation model of ORC system and the thermodynamic analysis model of ORC system are established. According to the design of system evaporator and condenser based on the given initial parameters, the tube length of finned tube evaporator is 159.6 m, the heat transfer area is 46.26 mm2, the plate number of plate condenser is 57, and the heat transfer area is 27.58 m2.According to the working medium screening principle of ORC system, Six commonly used circulating working fluids, R245faa R125faan R123AU R141bP134a and R236ea, are selected. On this basis, the reliability of the model is verified by using the results of literature. The effects of operating parameters (evaporation pressure, superheat degree, node temperature difference) and heat source temperature on the flow pressure drop are studied. And with the net output work, thermal efficiency? Efficiency, thermal recovery and irreversible loss are the evaluation indexes. The effect of flow pressure drop on the performance of ORC system is compared and analyzed. The results show that the flow pressure drop of ORC system is mainly composed of evaporator pressure drop. The evaporation pressure is the main factor affecting the pressure drop of the system. Considering the flow pressure drop, when the evaporation pressure is lower than 0.8 MPA, the decrease of the system performance will increase. For the dry working fluid, the effect of node temperature difference and superheat on the flow pressure drop is small. The effect of flow pressure drop on system performance is less than 10 under different node temperature differences, and the flow pressure drop increases with the increase of heat source temperature. In addition, the working fluid is an important factor affecting the system flow pressure drop and system performance. R141b and R245fa are the best working medium. 3) with the flow pressure drop, net output work, thermal efficiency and thermal recovery of ORC system as the optimization objectives, the thermodynamic parameters of evaporator (evaporation pressure, superheat degree, etc. The parameters of evaporator structure (tube length, pipe number, fin height, fin thickness and fin spacing) are used as design variables. Simulated annealing optimization algorithm is used to optimize the design of evaporator in ORC system. The influence of thermodynamic parameters and structural parameters of evaporator on the performance of ORC system is analyzed. The results show that there is a game and opposition phenomenon among the performance indexes of the system, and the evaporation pressure has the greatest influence on the objective function value of the thermodynamic parameters of the evaporator. The optimum evaporation pressure of R245fa is 2.5 MPA, and the fin structure is an important factor affecting the thermodynamic performance of the evaporator. For R245 faa, the optimized fin structure parameters are fin height 34mm, fin thickness 7.3mm, fin spacing 3.5mm.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM617

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