超临界水在倾斜上升管内的非均匀传热特性数值模拟

对超临界压力水在管径为Φ32mm×3mm、长度为8000mm、倾角为20°的倾斜光管内的流动与传热特性进行数值模拟研究,重点考察超临界水在大比热区内的奇异物性变化对倾斜管内的传热特性的影响.通过与实验数据的对比,验证计算模型的正确性;计算压力P=26,34 MPa时,不同质量流速和热负荷下倾斜光管内壁温随超临界水焓值增大而变化的规律,以及倾斜光管内壁周向温度及热负荷分布的不均匀性;分析大比热区管内上下母线处内壁温度差随工质焓值变化的特性及机理,讨论大比热区水的物性变化对倾斜光管内传热不均匀性的影响;引入截面横向动能与截面相对横向动能两个变量对二次流的强度进行描述,重点考察超临界水在大比热区内的二次流的流动特点及其对倾斜管内传热特性影响的机理.并利用截面中垂线上的密度梯度定量分析二次流变化的规律,讨论超临界压力下大比热区内倾斜光管内壁温分布异常的机理.

Numerical Simulation on Heterogeneous Heat Transfer in Water at Supercritical Pressures in Inclined Upward Tubes

Numerical simulation on flows and heat transfer of water at supercritical pressures in inclined upward smooth tubes of Φ32 mm ×3 mm at an angle of 20° respect to the horizon is made. Length of the tube is 8 000 mm. Influence of violent variation of water properties in the so-called "large specific heat region" on heat transfer characteristics was investigated. Numerical method was validated by comparing numerical results with experimental data. Variation of the inner surface temperature of tube wall with enthalpy of water, mass flow rate and heat flux were obtained at pressures of 26 MPa and 34 MPa, respectively. It was found that distributions of wall temperature, as well as heat flux, along tube wall' s circumference were non-uniform. Difference between top generatrix wall temperatures and the bottom generatrix wall temperature was analyzed. Effect of water properties in the so-call "large specific heat region" on heat transfer of water was also discussed. Two parameters, namely cross-section transverse kinetic energy and cross-section relative transverse kinetic energy were introduced to quantitatively describe intensity of secondary flow. And density grads along a cross-section perpendicular bisector were used to analysis secondary flow. Abnormal mechanism of inner wall temperature distribution in a large specific region in inclined upward tubes at supercritical pressures was discussed.