Sampling

Samples are withdrawn from the high-pressure shock tube through a port in the endwall of the driven section into two sample vessels. One vessel is used to collect a sample of the reagent mixture before the shock tube is fired. A sample of the gases after the shock tube has been fired is collected in the second vessel. The duration for which is a sample is collected has been determined empirically to ensure that only gases close to the end of the shock tube are taken when acquiring post-shock samples. The rig is configured so that when very condensable species are being sampled a ‘flush and sample’ method can be used. Additionally, the whole sampling rig can be purged with nitrogen and evacuated with a turbo pump independently of the shock tube.

The pictures on this page show the sampling rig attached to the high pressure shock tube. The large blue objects are air actuated valves that are controlled from a computer that ensures that samples are taken at the correct point in an experiment. The large silver coloured vessel close to the end of the shock tube collects the post-shock sample. The pre-shock sample vessel is much smaller and cannot be easily seen in these photographs.

Two views of the sampling rig attached to the high-pressure shock tube.