Mesoscopic modelling of heterogeneous boundary conditions for microchannel flows
Mesoscopic modelling of heterogeneous boundary conditions for microchannel flows
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DOI：
10.1017/s0022112005007512
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发表时间：
2005-02
影响因子：
3.7
通讯作者：
R. Benzi;Luca Biferale;M. Sbragaglia;S. Succi;F. Toschi
中科院分区：
文献类型：
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作者：
R. Benzi;Luca Biferale;M. Sbragaglia;S. Succi;F. Toschi
我们提出了微通道几何形状中流动的流体-壁相互作用的介观模型。我们为描述壁限单相流体的玻尔兹曼方程的离散版本定义了边界条件的合适实现。我们通过引入滑移函数来区分表面上的不同滑移特性，定义边界处流体动力场的局部滑移程度。滑移函数起着重正化因子的作用，它以某种程度的任意性结合了对介观描述的微观影响。我们讨论了滑移长度、滑移速度、压降减少（阻力减少）和微通道中质量流量的介观滑移特性，作为滑移程度及其空间分布和定位的函数，后者参数模拟了实际实验中超疏水材料的粗糙程度。我们还讨论了过渡状态下滑移长度的增量，即 ${O}(1)$ 克努森数。最后，我们将我们的结果与滑移长度对平均通道压力和局部滑移特性的依赖性的分子动力学研究以及压降减小对表面上沉积的疏水材料的百分比的实验依赖性进行比较。
We present a mesoscopic model of the fluid–wall interactions for flows in microchannel geometries. We define a suitable implementation of the boundary conditions for a discrete version of the Boltzmann equations describing a wall-bounded single-phase fluid. We distinguish different slippage properties on the surface by introducing a slip function, defining the local degree of slip for hydrodynamical fields at the boundaries. The slip function plays the role of a renormalizing factor which incorporates, with some degree of arbitrariness, the microscopic effects on the mesoscopic description. We discuss the mesoscopic slip properties in terms of slip length, slip velocity, pressure drop reduction (drag reduction), and mass flow rate in microchannels as a function of the degree of slippage and of its spatial distribution and localization, the latter parameter mimicking the degree of roughness of the ultra-hydrophobic material in real experiments. We also discuss the increment of the slip length in the transition regime, i.e. at ${O}(1)$ Knudsen numbers. Finally, we compare our results with molecular dynamics investigations of the dependence of the slip length on the mean channel pressure and local slip properties and with the experimental dependence of the pressure drop reduction on the percentage of hydrophobic material deposited on the surface.