球凸板对磁场中导电流体自由表面流动的传热强化

Heat transfer enhancement of free surface MHD-flow by protrusion wall

在许多工业应用和能源工程的磁流体流动传热中,外部磁场抑制导电流体的湍流脉动,降低了其对流传热系数。基于涡流发生的球凸板是一种高效的强化换热手段,其主要特点是传热强度大、流动阻力小、综合传热性能高,本文数值研究了利用球凸板强化磁场中导电流体自由表面流动换热的性能。计算采用磁场作用下的修正湍流模型和诱导磁场方程,并利用标量输运方程的求解器对它们进行求解。结果表明,在中等Hartmann数(30～70)下,球凸板的换热增强因子达到1.3～2.3,而阻力损失仅为光滑平板的1.34～1.45倍。在获得较高强化传热效果的同时,球凸板的阻力损失增加相对较小,因而获得了较高的综合传热性能。

Due to the magnetohydrodynamic （MHD） effect depressing heat transfer coefficients by pulsation suppression of external magnetic field on the electrical conducting fluid flow in many applications, the hemispherical protrusion wall was employed to free surface MHD-flow system as a heat transfer enhancement, because of its excellent characteristics, including high heat transfer coefficients, low friction factors and high overall thermal performance. The heat transfer characteristics of the free surface MHD-flow with hemispherical protrusion wall were simulated numerically by using the magnetic induction method and the modified turbulent equations, which were solved by the scalar transport equation solver. The results showed that in the range of Hartmann number 30-70, the protrusion wall assemblies could achieve heat transfer enhancement by about 1.3-2.3 relative to the smooth channel, with friction loss increase by about 1.34-1.45. Thus higher Nusselt number could be obtained by the protrusion wall with a smaller friction loss increase, resulting in much higher overall thermal performance.