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Modeling transient fully-developed natural convection in vertical ducts - Method of eigenfunction superposition

机译:在垂直管道中建模的瞬态完全开发的自然对流 - 特征叠加的方法

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This paper models the transient natural convection problem for the hydrodynamical and thermal fully-developed open vertical ducts. The powerful method of eigenfunction superposition yields analytic solutions for general duct cross sections. It is found that the induced flow rate approaches a constant in the steady state, but the transient depends on the Prandtl number (Pr). The rise time to reach 95% of steady state is 3/(Pr lambda(1)) if Pr 1, and is 3/lambda(1) if Pr 1, where lambda(1) is the lowest eigenvalue of the Helmholtz equation. The theory is then applied to the circular, semi-circular, rectangular and equilateral triangular ducts. For low Pr at small times, the transient induced velocity is larger in the velocity boundary layer near the walls but the maximum velocity is near the corners of the duct. (C) 2019 Elsevier Inc. All rights reserved.
机译:本文为流体动力和热完全开发的开放式垂直管道模拟了瞬态自然对流问题。特征功能卓越的强大方法产生了一般管道横截面的分析解决方案。发现诱导的流速在稳定状态下恒定地接近恒定,但瞬态取决于普朗特数(PR)。如果PR <1,如果Pr> 1,则为3 /λ(1),其中Lampda(1)是Helmholtz的最低特征值,达到95%的稳态稳定状态为3 /(PRλ(1))是3 /(Pr Lambda(1))方程。然后将该理论应用于圆形,半圆形,矩形和等边三角形管道。对于在较小次的低Pr,瞬态诱导的速度在壁附近的速度边界层中较大,但最大速度靠近管道的角落。 (c)2019 Elsevier Inc.保留所有权利。

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