【作者】 李智；

【导师】 俞小莉；

【作者基本信息】 浙江大学 ， 动力机械及工程， 2021， 博士

【摘要】 有机朗肯循环(Organic Rankine Cycle,ORC)因其较高的热效率、较简单的结构和高可靠性等优点,在中低品味余热回收领域拥有广泛的应用前景。当前针对有机朗肯循环的研究多是基于稳态热源进行的,但内燃机余热、工业余热等热源通常呈现波动和间歇特性,这给ORC的安全和高效运行带来了巨大挑战。针对余热源的非稳态问题,本文提出了集成相变储热换热器(Latent Thermal Energy Storage,LTES)的储热式ORC系统,利用相变材料(Phase Change Material,PCM)对非稳态热源进行预处理,使其达到下游ORC的安全运行条件。储热式ORC的成功实施仍面临许多亟待解决的基础问题,例如部件层面的储热换热器和系统层面的储热式ORC动态性能。围绕非稳态热源条件下储热式ORC的若干基础问题,本文的主要工作内容和结论如下:(1)基础ORC对非稳态热源的适应性及安全运行极限快速预测方法研究:探究了热源波动特性、蒸发器结构和材料参数对基础ORC阶跃变工况响应特性和循环变工况运行特性的影响,获得了最小过热度的变化规律,基于此建立基础ORC安全运行所允许的热源波动极限的快速预测方法。(2)非稳态热源对管壳式储热换热器的熔化过程影响机制及强化传热研究:探讨了不同热源波动特性对储热换热器的熔化过程影响机制,发现周期较小的波动热源对熔化过程影响较小,而周期较大的热源可以促进熔化过程。开展了基于肋片的储热换热器强化传热研究,结果表明储热换热器削弱热源波动的效果随着肋片高度的增加而更加显著。(3)PCM热物性参数对储热式ORC的动态运行特性的影响规律研究:分析了PCM热导率和熔点对热源阶跃变化和循环变化条件下储热式ORC动态性能的影响,结果表明储热换热器可以显著降低热源的波动幅度,且降低幅度随着PCM热导率的增加而增强。基于动态运行规律,获得了储热式ORC安全运行的热源波动极限快速预测关联式,结果表明储热式的安全运行极限明显高于基础ORC。(4)内燃机余热驱动的储热式ORC试验台架搭建及试验研究:开展了稳态工况、阶跃变工况和循环变工况条件下基础ORC和储热式ORC的性能对比试验研究,结果表明在阶跃变化比例较小时,储热式ORC能保证安全运行,在阶跃比例较大时可以延长过热度降至0的时间。循环变化热源条件下,储热式ORC可以保证安全运行,且平均理论净功和热效率较基础ORC分别提高23.5%和23.2%。(5)不同储热式ORC方案的性能初步探索研究。提出了储热换热器梯级布置的储热式ORC方案,以及热源-PCM-工质耦合传热的直接蒸发储热式ORC方案。对于PCM梯级布置的储热式ORC,分段数量N=2的方案较N=1和N=3的方案性能更佳。对于直接蒸发储热式ORC系统,不同直接蒸发储热式ORC方案的性能对比研究表明,相同时间内双LTES方案的总输出功和持续运行时长显著优于两种单LTES方案,且双LTES交替工作可以有效地克服单LTES的直接蒸发储热式ORC系统必须面临的间歇性运行问题。更多还原

【Abstract】 Organic Rankine cycle(ORC)has shown great potential in medium-to-low grade waste heat recovery,due to its relatively high thermal efficiency,simple structure and high reliability.Most of present studies about ORC were conducted based on steady heat source conditions,however,typical waste heat sources such as engine exhaust and industrial exhaust always present fluctuating characteristics,posing great challenges to the safe and efficient operation of ORC systems.Considering the fluctuation of many waste heat sources,ORC integrated with latent thermal energy storage(LTES)is proposed in this study,aiming to use phase change material(PCM)to weaken the fluctuation amplitude of dynamic heat source and ensure the safe operation of downstream ORC system.As a novel scenario,many fundamental problems need to be investigated and solved,such as the charging performance of LTES under fluctuating heat source and the dynamic performance of LTES-ORC system.This thesis focuses on solving these fundamental issues.Main tasks and conclusions are summarized as following:(1)Research on adaptation performance of basic ORC to fluctuating heat sources and fast prediction method for safe operating limitation.The effects of characteristics of fluctuating heat sources,parameters of evaporator on the step change and cyclic operating performance for basic ORC are comprehensively investigated.The variation trend of minimum superheat degree of basic ORC during the operating process is deduced,and the fast prediction method is established to obtain the maximum limitation of fluctuating amplitude of heat sources.(2)Research on the influence mechanism of unsteady heat sources on the melting process of shell-and-tube LTES and heat transfer enhancement techniques.The influence mechanism of fluctuation characteristics of different heat sources on the melting process of LTES is explored.It is found that effects of the fluctuation heat source with smaller periods are less on the melting process,while heat sources with larger periods can promote the melting process.Heat transfer enhancement based on fins for LTES is carried out,and results show that the effect of weakening the fluctuation of heat sources becomes more significant as the height of the fins increases.(3)Research on the influence of PCM thermo-physical parameters on dynamic operating characteristics of LTES-ORC.The influence of thermal conductivity and melting point of PCM on the dynamic performance of LTES-ORC under step-change and cyclic operating conditions is analyzed.LTES can significantly reduce the fluctuation range of heat sources,and the reduction range increases with the increase of the thermal conductivity of PCM.Based on the dynamic operation law,the fast prediction correlation formula is obtained to fast predict the maximum fluctuating amplitude of heat sources for the safe operation of the LTES-ORC,and the results show that the safe operation limit of LTES-ORC is significantly higher than that of the basic ORC.(4)Construction and experimental research of LTES-ORC test bench driven by the waste heat of the internal combustion engine.The performance comparison of the basic ORC and LTESORC under steady-state operating conditions,step change operating conditions and cyclic operating conditions has been experimentally compared.When the step change ratio is small,the LTES-ORC can ensure safe operation,and when the step ratio is large,the time for the superheat to drop to 0 can be prolonged.Under the condition of cyclically changing heat source,the thermal storage ORC can ensure safe operation,and the theoretical average net work and thermal efficiency are increased by 23.5% and 23.2% respectively compared with the basic ORC.(5)Preliminary investigation on performance of different novel LTES-ORC schemes.ORC system integrated with cascaded LTES and direct-evaporation ORC system integrated dual LTES are proposed.As for the former system,the number of segments of LTES N=2 possesses the best performance to overcome the fluctuation of heat source.As for latter system,the results indicates that ORC with double LTES can provide larger total output and work for longer time than other two ORC systems with only one LTES,meanwhile,the system with two LTES can effectively overcome the problems of intermittent operation that single-LTES ORC systems have to face.更多还原