竖直上升直肋管内超临界二氧化碳换热特性与肋结构优化

Heat transfer characteristics of supercritical carbon dioxide and structural optimization in vertical straightly-ribbed-tube

高性能超临界二氧化碳(S-CO_(2))换热器是实现S-CO_(2)布雷顿循环系统高效紧凑化的关键核心设备,S-CO_(2)在光滑通道内换热系数较低,寻求高换热性能与低阻换热结构是发展高效紧凑式换热器的关键。采用五轴电火花成型技术制造出直肋管,通过实验方法研究了S-CO_(2)在四头直肋管内传热规律,系统分析了流动参数对直肋管强化传热特性影响,定量评估了直肋管与光管换热能力的差异;采用数值模拟方法研究了直肋管结构参数对强化传热和阻力特性的影响规律,获得最优的直肋管结构。结果表明:增加压力和质量流速可以降低壁面温度,提高对流换热系数,直肋管的平均换热能力是圆形光管的1.96倍左右;相较于圆形光管,直肋管可以有效延迟传热恶化发生,且使传热恶化延迟能力提升0.3~1.8倍;当固定肋宽0.5 mm,肋高2.5 mm,直肋管的综合换热能力最好,综合换热因子为1.58;而固定肋高为0.5 mm,高宽比0.33,直肋管的综合换热能力最好,综合换热因子为1.22。

The high-performance supercritical CO_(2) heat exchanger is the key core equipment to realize the efficient and compact S-CO_(2) Brayton cycle system.S-CO_(2) has a low heat transfer coefficient in the smooth channel,and seeking high heat transfer performance and low-resistance heat transfer structure is the key to the development of efficient and compact heat exchangers.Five-axis EDM was used to fabricate the straightly ribbed tube,and the heat transfer behaviors of S-CO_(2) in the four-headed straight rib tube was experimentally studied,the effect of flow parameters on the heat transfer characteristics of the straight rib tube was systematically analyzed,and the difference in the heat transfer performance between the straight rib tube and the smooth tube was quantitatively evaluated.The influence of structural parameters on the enhanced heat transfer and resistance characteristics was studied by numerical simulation method,and the optimal straight rib tube structure was obtained.The results show that increasing the pressure and mass flow rate can reduce the wall temperature,improve the convective heat transfer coefficient,and the average heat transfer capacity of straight rib tube is about 1.96 times that of smooth tube.Compared with smooth tubes,straight ribbed tubes can effectively delay the occurrence of heat transfer deterioration,the ability to delay the occurrence of heat transfer deterioration by using straightly-ribbed tubes is increased by 0.3~1.8 times.When the fixed rib width W=0.5 mm and the rib height H=2.5 mm,the PEC is the best,and the value of PEC is1.58.However,the fixed rib height is H=0.5 mm,ε=0.33,and PEC of the straightly-ribbed tube is the best,with the value of PEC is 1.22.