Numerical Investigation of Natural Convection Dynamics in Open-Ended Vertical Channels with Different Aspect Ratios

TL;DR

This study numerically investigates natural convection in open-ended vertical channels with different aspect ratios, revealing flow acceleration near heated walls and the impact of aspect ratio on flow patterns and velocity profiles.

Contribution

It provides new insights into how aspect ratio influences natural convection flow patterns in open vertical channels using numerical simulations.

Findings

Flow accelerates near heated walls and decelerates near adiabatic walls.

Increasing aspect ratio reduces reverse flow.

Flow pattern near heated wall remains consistent despite aspect ratio changes.

Abstract

Understanding the thermal and flow fields associated with natural convection is of great importance in the design and manufacture of passive cooling systems, solar collectors, and ventilation systems. The aim of this study is to numerically investigate the naturally driven flow behaviour in open-ended vertical channels. Specifically, laminar airflow (Rayleigh number of 5*10^5) is naturally driven through a vertical channel that is asymmetrically heated with a uniform heat flux of (2043 w/m^2) . The compressible OpenFOAM solver (buoyantPimpleFoam) is employed, and open boundary conditions are applied at both the inlet and outlet to account for the effect of ventilation. The results exhibit good agreement with a numerical benchmark. Furthermore, a study of the airflow through two vertical channels, with two different aspect ratios of 5 and 31.25, is conducted. The results indicate that, in both cases of aspect ratios, the flow accelerates near the heated wall and decelerates near the adiabatic wall, forming a near-constant velocity region around the channel centreline. Increasing the aspect ratio diminishes the reverse flow. However, the flow pattern near the heated wall remains largely unaffected by aspect ratio changes. Additionally, the fluid behaviour downstream significantly affects velocity measurements at the inlet.