On the forced convective flow inside thermal collectors enhanced by porous media: from macro to micro-channels
On the forced convective flow inside thermal collectors enhanced by porous media: from macro to micro-channels
复制标题
多孔介质增强集热器内部的强制对流：从宏观到微通道
DOI：
--
复制
发表时间：
2021
期刊：
影响因子：
--
通讯作者：
S. Rashidi
中科院分区：
文献类型：
--
作者：
M. Dehghan;Zahra Azari Nesaz;A. Pourrajabian;S. Rashidi
目的
为了得到空气基太阳能集热器内部的速度分布和泊松叶数等流动特征参数，本研究对空气基太阳能集热器中常用的填充多孔介质的矩形通道内的三维强迫对流流动进行了研究。考虑了流体流动的最一般模型(即滑移和无滑移边界条件下的非线性Darcy-Brinkman-Forchheimer偏微分方程组)。
设计/方法/方法
基于摄动技术对一般控制方程进行了解析求解，并与基于非均匀结构网格上的有限差分解的数值模拟结果进行了验证。
发现
得到了上述一般情况下基于指数函数的速度分布解析解，并相应地给出了PO的表达式。结果表明，随着风道长宽比的增大，速度分布趋于均匀。此外，还提出了动量方程中非线性阻力项(即Forchheimer项)的考虑和忽略准则。根据敏感性分析，结果表明，只有在高达西数的多孔介质中，非线性阻力项对努塞尔数的影响才是重要的。
原创性/价值
在一般的Darcy-Brinkman-Forchheimer模型和包括无滑移和滑移两种流型的一般边界条件下，得到了填充多孔介质的矩形管道内三维强迫对流流动的一般解析解。得到了计算PO数的解析表达式，可用于工程估算，为数值模拟的验证提供了依据。文中还介绍了动量方程中考虑/忽略非线性阻力项的判据。
Purpose
Aiming at finding the velocity distribution profile and other flow characteristic parameters such as the Poiseuille (Po) number, this study aims to focus on the three-dimensional forced convective flow inside rectangular ducts filled with porous media commonly used in air-based solar thermal collectors to enhance the thermal performance. The most general model for the fluid flow (i.e. the non-linear Darcy–Brinkman–Forchheimer partial differential equation subjected to slip and no-slip boundary conditions) is considered.
Design/methodology/approach
The general governing equations are solved analytically based on the perturbation technique and the results are validated against numerical simulation study based on a finite-difference solution over a non-uniform but structured grid.
Findings
The analytical velocity distribution profile based on exponential functions for the above-mentioned general case is obtained, and accordingly, expressions for the Po are introduced. It is found that the velocity distribution tends to be uniform by increasing the aspect ratio of the duct. Moreover, a criterion for considering/neglecting the nonlinear drag term in the momentum equation (i.e. the Forchheimer term) is proposed. According to the sensitivity analysis, results show that the nonlinear drag term effects on the Nusselt number are important only in porous media with high Darcy numbers.
Originality/value
A general analytic solution for three-dimensional forced convection flows through rectangular ducts filled with porous media for the general model of Darcy–Brinkman–Forchheimer and the general boundary condition including both no-slip and slip-flow regimes is obtained. An analytic expression to calculate Po number is obtained which can be practical for engineering estimations and a basis for validation of numerical simulations. A criterion for considering/neglecting the nonlinear drag term in the momentum equation is also introduced.