超临界压力区倾斜上升光管壁温分布与传热特性的试验研究

Experimental Research on Wall Temperature Distribution and Heat Transfer Characteristics of the Tilted Smooth Riser Tubes in the Supercritical Pressure Region

在超临界压力下,对倾角α=20°的φ25×2.5(mm)不锈钢倾斜上升光管内水的传热特性及管壁温分布进行了试验研究.试验参数范围:p=23～28 MPa,质量流速G=600～1200 kg/(m2s),平均内壁热流密度q=300～600 kW/m2.试验结果表明:倾斜管壁温及传热系数沿周向分布不均匀;不均匀分布特性在不同焓值区不同;在略低于拟临界焓值区,管壁面换热系数有一个峰值;提高质量流速可减小不均匀性,压力对拟临界焓值区的传热特性和不均匀性影响较明显;内壁平均热流密度对不均匀性和传热的影响大,在较低热流密度时,上母线温度最高,下母线的温度最低,而在高热流密度时,侧面的温度最高.并研究了因为浮力引起的自然对流对不均匀性的影响.

Experimental research under supercritical pressure conditions has been carried out on heat transfer characteristics of water within 20° tilted smooth riser tubes of φ25×2.5mm stainless steel as well as on their wall temperature distribution. The pressures range concerned was from 23 to 28 MPa, mass flow velocity varied between 600 and 1200kg/m^2s, with the mean heat flux crossing the inner tube surface varying from 300 to 600 kW/m^2 . Experimental results indicated that the temperature distributions along the wall＇ s circumference as well as the heat transfer were nonuniform, with the degree of nonuniformity changing in different regions of enthalpy. A peak heat transfer coefficient can be observed in the region somewhat below the pseudocritical enthalpy. The nonuniformity can be reduced by increasing mass flow. Heat transfer and nonuniformity in the pseudocritical enthalpy region are remarkably influenced by pressure. The mean heat flux crossing the inner tube surface also has a great influence on nonuniformity and heat transfer. At moderate heat flux, a maximal wall temperature appears at the top of the tube＇ s cross-section, and a minimum wall temperature will appear at the bottom; whereas the maximal wall temperature will appear at the lateral side of the cross-section in case of high heat flux. The influence of natural convection, caused by buoyance, on nonuniformity also has been studied. Figs 6 and refs 9.