近临界压力区垂直内螺纹管临界热流密度实验研究

Experimental Investigation on Critical Heat Flux in Vertical Rifled Tube of Near-critical Pressure Region

在近临界压力区,对垂直上升内螺纹管流动沸腾的偏离泡核沸腾(DNB)型临界热流密度(CHF)现象进行了实验研究。试验段采用ф35 mm×5.67 mm六头内螺纹管。实验参数范围为:压力18~21 MPa,质量流速500~1 000kg/(m^2·s),进口过冷度3~5℃,内壁热负荷40~960kW/m^2。实验得到了不同工况下的内壁温度和传热系数分布特性,分析了流动参数对内螺纹管中DNB型CHF的影响,并根据实验数据拟合出两相区的传热关联式与临界热流密度(qCHF)预测关联式。内螺纹管的qCHF实验数据被用于与光管的qCHF预测值进行对比,发现内螺纹管具有一定的CHF强化作用,但当压力越靠近临界压力时这种作用会被抑制甚至消失。实验结果表明:在近临界压力下,内螺纹管会在低干度区甚至过冷区发生DNB现象,压力的增大和质量流速的减小均会使DNB提前发生。qCHF随压力的减小和质量流速的增大而增大。在特定工况下,试验段不同截面会分别发生偏离泡核沸腾与蒸干。

In near-critical pressure region,for the purpose of investigating critical heat flux（CHF）of departure from nucleate boiling（DNB）in a vertical upward rifled tube,the experiment was conducted with the range of pressure from 18 to 21 MPa,mass flux from 500 to 1 000 kg/（m^2·s）,inlet subcooling temperature from 3 to 5 ℃ and inner wall heat flux from 40 to 960 kW/m^2 in a six-head rifled tube with the size of ф35 mm×5.67 mm.The inner tube wall temperature and heat transfer coefficient distribution in different operating conditions were obtained in the experiment.The effects of the operating parameters on CHF were analyzed.Meanwhile,based on the experimental data,aheat transfer correlation utilized in two-phase region and an empirical correlation used to predict the critical heat flux recorded as qCHF were developed.Moreover,experimental qCHFin the rifled tube was compared with predicted qCHFin smooth tube,revealing the enhancement effect of CHF in rifled tube.The experimental results show that at nearcritical pressure,DNB can occur at low vapor quality and even in subcooled region in rifled tube.The increase of pressure and the decrease of mass flux can both lead to the earlier occurrence of DNB.Meanwhile,qCHFincreases with the decrease of pressure and the increase of mass flux.In addition,in specific operating conditions,DNB and dryout can coexist at different sections of the rifled tube respectively.