Studying Convective Flow in a Vertical Solar Chimney at Low Rayleigh Number by Lattice Boltzmann Method: A Simple Method to Suppress the Reverse Flow at Outlet

摘要

Solar chimneys absorb solar radiation heat and induce natural convective airflow for natural ventilation of buildings. In this study, we simulate induced airflow in a two-dimensional vertical solar chimney by Lattice Boltzmann Method (LBM) and focus on laminar flow region at low Rayleigh (Ra) number. Standard D2Q9 and D2Q4 models with single relaxation time are used for flow and temperature fields, respectively. Airflow and air temperature distributions inside the chimney are investigated under effects of main parameters of solar chimneys: heat flux, chimney height H, and chimney width b. Typical characteristics of a solar chimney were well reproduced in our simulations. Particularly, we analyze flow reversal region near the outlet of the chimney. The flow separation regions were observed at low ratio of H/b at a given Ra number or at high Ra number at a given H/b ratio and significantly reduced the induced flowrate. To suppress the flow reversal, we propose a simple method of rearranging the heat transfer surface on the opposite side in the upper and lower halves of the chimney. The results show that this method can eliminate the separation region and increases the induced flowrate at low ratio of H/b at a given Ra number.