Abstract: In order to study the gas mixing uniformity in the ventilation duct under various flow status, we established a simulation model by using computational fluid dynamics method. The Reynolds number covers the range of 800 to 70 000. The simulation results showed that: the change of Reynolds number has an important influence on the velocity distribution; When the height is less than 8 times hydraulic diameter, the velocity distribution will become more uniform when the monitoring surface is raised. In the region of more than 8 times hydraulic diameter, increasing the degree of turbulence can improve the uniformity of velocity distribution. However, when the flow state reaches full turbulence, it is not beneficial to increase the Reynolds number. For the tracer gases, they could reach a sufficient mixing in each monitoring surface. When the Reynolds number is lower than 29 000, the mixing uniformity of the tracer gas on each surface will slightly decrease as the Reynolds number increases. But when the Reynolds number exceeds 29 000, the uniformity of mixing is no longer significant. Comparing the simulation results with the test results, the simulation results of wind speed and tracer gas concentration are in good agreement with the test measurements.

Key words: gaseous effluent monitoring, computational fluid dynamics, gas mixing uniformity