摘要
[目的]CO_(2)布雷顿循环在能源动力转换领域具有广阔的应用前景.在实际工程应用中,循环常处于亚临界和超临界工况,因此,深入了解研究亚临界和超临界压力工况下CO_(2)的流动传热特性对系统的安全运行至关重要.[方法]本研究利用CO_(2)流动传热实验台架,探究了在管径10 mm的竖直圆管中,热通量在38.4~439.1 kW/m^(2)范围内的亚临界和超临界CO_(2)的传热特性.[结果]低热通量下,亚临界压力工况下的CO_(2)传热能力强于超临界压力工况下的CO_(2);当压力接近拟临界区时CO_(2)的流动传热特性与超临界CO_(2)的传热特性相似;随着热通量的增加,亚临界和超临界压力工况下均会出现传热恶化现象,超临界压力工况下CO_(2)传热会出现传热恶化—传热恢复—传热正常的转变现象.[结论]本研究探析了CO_(2)在不同工况下的传热现象,对实际工程应用具有指导意义.尤其是高热通量下的实验现象差异表明亚临界压力工况比超临界压力工况对热力设备构成的威胁更大.同时,超临界压力工况下传热恶化恢复与恶化位置固定等现象有进一步研究的价值,值得深入挖掘.
[Objective]Compared to other thermodynamic cycles,the supercritical CO_(2)(S-CO_(2))recompression Brayton cycle exhibits a relatively high thermal efficiency,while maintaining a relatively simple cycle arrangement.It demonstrates significant efficiency in the temperature range of 400700℃.The CO_(2) Brayton cycle system has broad application prospects in the field of power cycle electricity generation.It has garnered widespread attention in applications such as solar energy carbon capture and storage in coal-fired power plants,waste heat utilization,and GenerationⅣnuclear power systems.Furthermore,the CO_(2) Brayton cycle frequently operates under both subcritical and supercritical conditions in industrial applications.Therefore,it is crucial to have a thorough understanding of the flow and heat transfer characteristics of CO_(2) under subcritical and supercritical pressures for the safe operation of the system.However,current research predominantly focuses on the heat transfer characteristics of CO_(2) under supercritical pressure and low heat flux.In this study,the heat transfer characteristics of subcritical and supercritical CO_(2) in a vertical circular tube are investigated to address the data gap under high heat flux conditions and provide guidance for practical engineering applications.[Methods]Based on the experience of domestic and international scholars in building supercritical fluid test benches,appropriate instruments and equipment have been selected to construct an CO_(2) forced circulation bench at the School of Energy,Xiamen University.The entire test bench has a rectangular structure with a height of 2.6 m and a length of 8.6 m.The outer wall temperature was measured by welding armored thermocouples onto the outer surface of the test section.The main circuit consists of uniform 316L stainless steel pipes withΦ10 mm×1.5 mm,while the test section was made of Incoloy800H pipes withΦ14 mm×2 mm.These pipes have undergone bright annealing treatment.The test section was heated by a 75 kW DC power supply and insulated with a 60 mm thick aluminum silicate ceramic fiber insulation blanket and 100 mm thick rock wool insulation pipe.[Results]The results indicate that at low heat flux,the heat transfer capacity of CO_(2) under subcritical pressure was greater than that under supercritical pressure.At a heat flux about 155 kW/m^(2),heat transfer deterioration occurred in CO_(2) at 4.8 MPa,while no such deterioration was observed in CO_(2) at supercritical pressure(8.8 MPa).Following heat transfer deterioration,the heat transfer capacity of CO_(2) under subcritical pressure conditions decreased sharply,with the heat transfer coefficient approaching that observed under supercritical pressure conditions.CO_(2) at pressures of 4.8 and 6.2 MPa exhibited similar heat transfer characteristics under subcritical conditions,although subtle differences in heat transfer deterioration were observed.CO_(2) at a pressure of 9.5 MPa was in a supercritical state in the test section,and its heat transfer characteristics at low heat flux were consistent with those at 8.8 MPa,while heat transfer deterioration occurred at higher heat flux.The heat transfer deterioration of CO_(2) at 7.1 and 9.5 MPa pressure conditions was similar,occurring at 0.15 m in the test section,followed by recovery of heat transfer after deterioration.[Conclusion]As the pressure approaches the pseudo critical zone,the flow and heat transfer characteristics of CO_(2) become similar to those of S-CO_(2),and it s worth mentioning that CO_(2) exhibits a phenomenon where heat transfer deterioration is followed by heat transfer recovery and then a return to normal heat transfer.As the heat flux increases,heat transfer deterioration occurs under both subcritical and supercritical pressure conditions.However,heat transfer deterioration occurs at a lower heat flux under subcritical conditions compared to supercritical conditions and is more dangerous under subcritical conditions.This pattern implies that the subcritical pressure condition poses a greater threat to thermal equipment than supercritical pressure conditions.
作者
卢功豪
张广旭
张文佳
谢榕顺
王海鑫
洪钢
张尧立
LU Gonghao;ZHANG Guangxu;ZHANG Wenjia;XIE Rongshun;WANG Haixin;HONG Gang;ZHANG Yaoli(College of Energy,Xiamen University,Xiamen 361102,China;Beijing Institute of Spacecraft System Engineering,Beijing 100094,China;Fujian Research Center for Nuclear Engineering,Xiamen 361105,China)
出处
《厦门大学学报(自然科学版)》
北大核心
2025年第1期169-176,共8页
Journal of Xiamen University:Natural Science
基金
厦门市自然科学基金(3502Z202373016)。
关键词
超临界CO_(2)
传热恶化
高温工况
高热通量
supercritical CO_(2)
heat transfer deterioration
high-temperature condition
high heat flux
