太阳能腔式熔盐吸热器随时空变化的光-热-力耦合一体化方法、机理分析及其失效准则研究

Study on the coupled photon-thermal-stress integration method,characteristics with time and failure criterion in the solar molten salt cavity receiver

基于本团队前期已提出的蒙特卡洛光线追迹(MCRT)与杰勃哈特(Gebhart)方法耦合的光学模型,在综合考虑了吸热器内复杂的导热-对流-辐射耦合换热过程的前提下,建立了塔式系统中熔盐吸热器的光-热-力耦合的一体化数值分析模型.基于此模型,探讨了典型工况下吸热器的太阳辐射能流、温度以及热应力的时空分布特性,并考察了不同管材导热性能、熔盐流路布置方式对吸热器的光-热-力耦合特性的影响规律;最后提出了光-热-力耦合条件下腔式熔盐吸热器应力失效的临界能流密度判定准则.结果表明:非均匀的辐射能流对吸热器的温度与热应力影响显著,温度与热应力分布也呈强烈非均匀性;辐射能流与热应力随时空变化显著,但温度变化不明显,正午时刻辐射能流与热应力峰值最高,与上午11时和下午13时相比,峰值热应力分别增加11%与10%;不同管材对热应力的影响较为显著,采用高导热性能的吸热管材可有效降低热应力,与800H管材相比,采用高导热性能的316H管材峰值热应力可降低37%;采用低能流区向高能流区的熔盐流路布置方式吸热器温度分布更均匀,有利于降低热应力峰值,与相反的流路布置相比,峰值热应力可降低20%;管材断裂韧性可作为判断熔盐吸热器应力失效的重要指标,由本文提出的应力失效的临界能流密度判定准则表明,管材断裂韧性劣化越严重,导致吸热器应力失效的临界能流密度越低,增加吸热器失效的风险.

In this paper, the studies on the characteristics with time and failure criterion in the solar molten salt cavity receiver are carried out based on the coupled photon-thermal-stress integration method. Especially, the truly non-uniformed solar heat flux in the cavity receiver with different time are simulated using the optical simulation approach coupling the Monte Carlo ray tracing and Gebhart methods proposed by our team. Besides, the complex coupled heat transfer process of conduction, convection and radiative in the receiver are also comprehensively considered. Based on the integrally model, the solar flux, temperature and thermal stress on the absorber surfaces with different time are obtained. Then, the influ- ences of different tube materials, flow layouts of molten salt on the coupling performances of photon-thermal-stress conversion process are discussed. Finally, the stress failure criterion in the molten salt cavity receiver is proposed based on the fracture mechanics theory. The results show that the temperature and thermal stress are influenced significantly by the non-uniformed solar flux, the distribution of temperature and thermal stress are also extremely non-uniformed. The solar flux and thermal stress change remarkably with different time, the peak heat flux and stress are maximum at 12：00 noon, and the peak thermal stress could increase by 11% and 10% compared with 11：00 and 13：00. It is also found that the peak thermal stress would be reduced effectively when the receiver tube with better thermal conductivity property and the molten salt flow layout which is from low-flux area to high-flux area are adopted. For example, compared with 800H receiver tube, the peak thermal stress of 316H tube could be reduced by 37%. Meanwhile, the peak thermal stress of flow layout which is from low to high flux area would be 20% lower than that with the opposite layout. The fracture toughness of receiver tube, which is influenced by the molten salt corrosion, is one of the key parameters to assess stress failure. Based on the stress failure criterion of critical solar flux proposed by this paper, the critical heat flux of stress failure would exhibit a decreasing trend when the fracture toughness degradation is serious in the molten salt receiver.