双分散多孔介质圆管通道中骨架发热对强迫对流传热的影响

多孔介质填塞是传热强化的有效方法之一。与单分散(普通)多孔介质相比,双分散多孔介质含有多孔骨架相和裂纹相,流体充满裂纹相(大孔隙)和多孔骨架相内小孔隙,因此具有更大的比表面积。基于双速度-双温度模型,分析了恒热流边界条件下双分散多孔介质圆管通道的强迫对流传热,并推导了两相的无量纲温度以及Nu的解析解。参数分析表明,多孔骨架发热会在通道壁-双分散多孔介质交界面上出现热流(温度梯度)分岔现象,并从数学和传热学角度阐释了其发生机理。在骨架吸热情形下,单分散和双分散多孔介质通道的Nu均呈现不连续特征,而对于双分散多孔介质通道,当有效导热系数比较大时,这种不连续特征仅出现在骨架生热情形。并且分析了Nu的渐近行为。

Effects of Heat-Generating Matrix on the Forced Convective Heat Transfer in a Circular Duct Filled with a Bidisperse Porous Medium

Porous medium filling is one of the effective approaches for the heat transfer enhancement. Compared to the monodisperse (regular) porous medum (MDPM), the bidisperse porous medium(BDPM) includes the porous phase and fracture phase. The fluid satuates the fracture phase (micropores) and the fraction of porous phase (micropores), which makes much larger specific surface area. Based on the two-velocity two-temperature model, the forced convective heat transfer in a circular duct filled with a bidisperse porous medium is analyzed under the constant heat flux boundary condition. And the analytical solutions for dimensionless temperatures of two phases as well as Nusselt number are derived. The parametric study illustrates that the heat-generating porous matrix leads to the phenomenon of heat flux (temperature gradient) bifurcation at the interface between the duct wall and the BDPM. From the mathematical and heat transfer view, the occurrence mechanism of this phenomenon is explained. For the case of heat-absorbing matrix, the Nusselt numbers for both MDPM and BDPM ducts exhibit the non-continuous characteristics. However, when the effective thermal conductivity ratio becomes larger, this non-continuity occurs only in the case of heat-generating matrix.Finally, the asymptotic behaviorof Nusselt number is also investigated.