To monitor emissions from coal-fired power plants, technicians need to measure the rate at which flue gas is emitted from the smokestack. The flow inside the smokestack contains eddies and swirls but generally travels upwards. In the NIST tests, four probes -- called pitot tubes -- are inserted horizontally into the smokestack. The four probes each take a flow measurement at four different spots, for a total of 16 measurements. With this information, NIST scientists could test the precision and accuracy of a new pitot tube design and measurement method.
