内螺纹管中超临界水的传热数值模拟

Numerical Simulation of Supercritical Water Heat Transfer in Rifled Tubes

通过数值模拟研究了超临界水在半周加热内螺纹管中的流动传热过程。采用SST k-ω湍流模型求解流固耦合换热,在压力25 MPa、质量流速600 kg/(m^(2)·s)、热流密度分别为280 kW/m^(2)和470 kW/m^(2)条件下研究了螺纹高度、螺距和螺纹形状等结构参数对超临界水传热的影响,比较了全周加热和半周加热条件下螺纹结构参数对传热的影响差异,揭示了螺纹结构参数变化引起的传热强化机理。结果表明:与全周加热相比,半周加热条件下螺纹结构参数增强了对加热侧换热性能的影响,削弱了对整体平均换热性能的影响,冷侧壁面温度主要受周向导热的影响,仅与热流密度有关,不同螺纹结构参数下冷侧温度分布几乎没有变化;当浮升力准则数Bo>10^(-5)时,优化螺纹结构对改善超临界水换热性能的效果更突出,增大螺纹高度、减小螺距能够强化换热,矩形内螺纹管的换热性能优于梯形内螺纹管;旋流是内螺纹管中超临界水传热强化的主要因素,结构参数主要通过强化边界层30<y+<100区域内的旋流强度,最终实现管内超临界水换热性能的提升。

The flow and heat transfer process of supercritical water in a half cycle heated internally threa⁃ded tube was studied through numerical simulation.The SST k⁃ωturbulence model was used to solve the fluid⁃structure interaction heat transfer.The effects of the screw thread height,pitch and shape on the heat transfer of supercritical water were studied under the conditions of pressure 25 MPa,mass flow rate 600 kg/(m^(2)·s),and heat flux density 280 kW/m^(2)and 470 kW/m^(2),respectively;the difference in the influence of thread structure parameters on heat transfer under full cycle heating and half cycle heating conditions was compared,and the heat transfer enhancement mechanism caused by changes in screw structure parameters was revealed.The results show that compared with the full cycle heating,the screw thread structure parameters under the half cycle heating condition enhance the influence on the heat trans⁃fer performance of the heating side,and weaken the influence on the overall average heat transfer per⁃formance.The cold side wall temperature is mainly affected by the circumferential heat conduction,only related to the heat flow density,and the cold side temperature distribution has almost no change under different screw thread structure parameters;when the buoyancy criterion number Bo>10-5,optimizing the threaded structure has a more prominent effect on improving the heat transfer performance of supercrit⁃ical water.Increasing the threaded height and reducing the pitch can enhance heat transfer,and the heat transfer performance of rectangular rifled tubes is better than that of trapezoidal rifled tubes;swirl flow is the main factor for heat transfer enhancement of supercritical water in rifled tubes.The structural parame⁃ters mainly enhance the swirling strength in the 30<y+<100 region of the boundary layer,and ultimate⁃ly improve the heat transfer performance of supercritical water in tubes.