Computational modeling of woodstove pollutants in dilution tunnels

The computational modeling of the dilution tunnels used for experimental measurement of the woodstove pollution was presented. Two EPA-approved test labs for residential wood heat appliances, referred to as Lab-1 and Lab-2 dilution tunnels were simulated. The Ansys-Fluent software was enhanced with the addition of user-defined functions (UDF) and was used to simulate the airflow velocity, temperature, and particle concentration in the dilution tunnels. Particular attention was given to the variation of concentration profile at the test section and its uniformity. The simulation results suggested that roughly uniform or somewhat non-uniform particle concentrations entering from the woodstove stack into the dilution tunnel led to the uniform concentration at the outlet of the tunnel. This is particularly the case for the Lab-1 dilution tunnel. However, for the Lab-2 dilution tunnel, a highly non-uniform concentration at the woodstove stack outlet flowing at a high velocity into the dilution tunnel led to a non-uniform profile for the particle concentration at the test section. For this case, replacing the second elbow that is downstream from the mixing section with a tee reduced the nonuniformity of the concentration profile at the tunnel outlet. Implications: This study numerically investigated two dilution tunnels used in EPA-approved test labs. The dilution tunnel is used to dilute and cool the exhaust flow of the woodstove's stack. A properly working dilution tunnel provides a uniform concentration at the test section. Under different conditions, particulate matter (PM) laden turbulent flows in the tunnels are simulated to assess the dilution tunnel's performance. The goal is to understand the conditions that the dilution tunnels provide uniform concentration at their test section. The presented results suggest that using a tee instead of an elbow would enhance mixing and the chance for generating uniform concentration at the test section.