Heat and momentum transfer to a particle in a laminar boundary layer
Heat and momentum transfer to a particle in a laminar boundary layer
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DOI：
10.1017/jfm.2020.45
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发表时间：
2020-02
影响因子：
3.7
通讯作者：
A. Lattanzi;Xiaolong Yin;C. Hrenya
中科院分区：
文献类型：
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作者：
A. Lattanzi;Xiaolong Yin;C. Hrenya
在许多工业系统中，边界壁或浸入表面被用作加热气固混合物的主要热源。先前解决固体在边界附近的传热问题的努力涉及将无界对流关联扩展到近壁区域，并结合间接传导的粒子尺度理论。此外，在近壁区域（不加修饰）利用无界阻力相关性来解析流体施加在固体颗粒上的力。我们严格测试无界相关性和间接传导理论对输出的直接数值模拟层流通过一个热板和一个静态的，冷的粒子。在这里，局部变量被用于与未解决的计算流体动力学离散元方法的一致性，并导致与自由流变量获得的自相似的新的无界相关性。新的与局部流体速度的阻力相关性捕获了无界系统和近壁区域的阻力，而经典的与自由流动流体速度的无界阻力相关性显着过度预测了近壁区域的阻力。类似地，发现经典的无界对流关联低估了发生在近壁区域的传热。除了无界对流外，还包括间接传导，性能明显更好。为了考虑边界效应，我们建立了一个新的努塞尔关系式，用于超越局部无界对流的传热。多余的壁面努塞尔数仅依赖于无因次的粒子-壁面分离距离，当粒子-壁面分离距离较大时，多余的壁面努塞尔数渐近衰减为零，将无界区和近壁区拼接在一起。
Bounding walls or immersed surfaces are utilized in many industrial systems as the primary thermal source to heat a gas–solids mixture. Previous efforts to resolve the solids’ heat transfer near a boundary involve the extension of unbounded convection correlations into the near-wall region in conjunction with particle-scale theories for indirect conduction. Moreover, unbounded drag correlations are utilized in the near-wall region (without modification) to resolve the force exerted on a solid particle by the fluid. We rigorously test unbounded correlations and indirect conduction theory against outputs from direct numerical simulation of laminar flow past a hot plate and a static, cold particle. Here, local variables are utilized for consistency with unresolved computational fluid dynamics discrete element methods and lead to new unbounded correlations that are self-similar to those obtained with free-stream variables. The new drag correlation with local fluid velocity captures the drag force in both the unbounded system as well as the near-wall region while the classic, unbounded drag correlation with free-stream fluid velocity dramatically over-predicts the drag force in the near-wall region. Similarly, classic, unbounded convection correlations are found to under-predict the heat transfer occurring in the near-wall region. Inclusion of indirect conduction, in addition to unbounded convection, performs markedly better. To account for boundary effects, a new Nusselt correlation is developed for the heat transfer in excess of local, unbounded convection. The excess wall Nusselt number depends solely on the dimensionless particle–wall separation distance and asymptotically decays to zero for large particle–wall separation distances, seaming together the unbounded and near-wall regions.