幂律流体管内充分发展的对流换热分析

将非牛顿流体的动量方程、能量方程和幂律流体的本构方程相结合 ,建立了幂律流体管内流动和换热充分发展时的对流换热控制方程组 ,并在恒热流和恒壁温边界条件下分别对方程组进行了求解 ,得到了两种不同边界条件下的温度分布和无量纲对流换热系数 (Nu数 )的表达式。结果表明 ,幂律流体的流变指数对流体流动的影响要大于对换热的影响 ;在恒热流边界条件下 ,幂律流体的温度在管内沿轴向呈线性分布 ;而在恒壁温条件下 ,其截面平均温度沿轴向呈指数规律变化。幂律流体的无量纲对流换热系数与幂律流体的流变指数有关 ,并且在两种边界条件下 ,均随着流变指数的增加而减小

Analysis on fully developed convective heat transfer of power law fluid flowing in tube

Combining the momentum equation and energy equation of non-Newtonian fluid with the constitutive equation of power-law fluid,a mathematical model for fully developed convective heat transfer of power law fluid flowing in tube was set up. The model was solved under the constant heat flux boundary and the constant wall temperature boundary conditions respectively. The temperature profiles and the local convective heat transfer coefficient were derived under the two boundary conditions. The results show that the effect of rheologic index of power-law fluid on the flow is greater than that on the heat transfer. The temperature profile of the power-law fluid along the axial direction is linear under the constant heat flux boundary condition, while the temperature profile at the constant tube-wall temperature is exponential along the flowing direction. The expressions of Nusselt number show that the rheologic index of the power-law fluid has some effect on the Nusselt number. The Nusselt number of the power-law fluid decreases with the increase of rheologic index under the two boundary conditions.