Improvement of a wind-tunnel sampling system for odour and VOCs

Wind-tunnel systems are widely used for collecting odour emission samples from surface area sources. Consequently, a portable wind-tunnel system was developed at the University of New South Wales that was easy to handle and suitable for sampling from liquid surfaces. Development work was undertaken to ensure even air-flows above the emitting surface and to optimise air velocities to simulate real situations. However, recovery efficiencies for emissions have not previously been studied for wind-tunnel systems. A series of experiments was carried out for determining and improving the recovery rate of the wind-tunnel sampling system by using carbon monoxide as a tracer gas. It was observed by mass balance that carbon monoxide recovery rates were initially only 37% to 48% from a simulated surface area emission source. It was therefore apparent that further development work was required to improve recovery efficiencies. By analysing the aerodynamic character of air movement and CO transportation inside the wind-tunnel, it was determined that the apparent poor recoveries resulted from uneven mixing at the sample collection point. A number of modifications were made for the mixing chamber of the wind-tunnel system. A special sampling chamber extension and a sampling manifold with optimally distributed sampling orifices were developed for the wind-tunnel sampling system. The simulation experiments were repeated with the new sampling system. Over a series of experiments, the recovery efficiency of sampling was improved to 83-100% with an average of 90%, where the CO tracer gas was introduced at a single point and 92-102% with an average of 97%, where the CO tracer gas was introduced along a line transverse to the sweep air. The stability and accuracy of the new system were determined statistically and are reported.