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

Wind-tunnel systems are widely used for collecting occur emission samples f rom surface area sources. Consequently, a portable wind-tunnel system was d eveloped at the University of New South Wales that was easy to handle and s uitable for sampling from liquid surfaces. Development work was undertaken to ensure even air-flows above the emitting surface and to optimise air vel ocities to simulate real situations. However, recovery efficiencies for emi ssions have not previously been studied for wind-tunnel systems. A series o f experiments was carried out for determining and improving the recovery ra te 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 we re initially only 37% to 48% from a simulated surface area emission source. It was therefore apparent that further development work was required to im prove recovery efficiencies. By analysing the aerodynamic character of air movement and CO transportation inside the wind-tunnel, it was determined th at the apparent poor recoveries resulted from uneven mixing at the sample c ollection point. A number of modifications were made for the mixing chamber of the wind-tunnel system. A special sampling chamber extension and a samp ling manifold with optimally distributed sampling orifices were developed f or the wind-tunnel sampling system. The simulation experiments were repeate d 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%, wher e the CO tracer gas was introduced at a single point and 92-102% with an av erage of 97%, where the CO tracer gas was introduced along a line transvers e to the sweep air. The stability and accuracy of the new system were deter mined statistically and are reported.