Continuous monitoring of binary gas mixture concentration with applicationto turbine blade cooling experiments

Turbine blade cooling experiments often use mixtures of air and a heavy gas (CO2, SF6) to simulate coolant/mainstream density ratios. If the mixing of the mainstream with the coolant ejected from the blade is of interest, the n it may be necessary to determine the spatial distribution of the heavy ga s concentration in the flowfield. Commercial analyzers are too slow and hav e other disadvantages when used for this purpose. To meet this special need a device has been developed to monitor the heavy gas concentration continu ously in a small sample stream by determining the speed of sound in the sam ple. Together with the temperature of the sample, the information is suffic ient to determine the concentration. The device measures the time of propag ation for an ultrasonic burst transverse to the stream. The temperature of the gas contained in the device is controlled and measured. Calibration wit h several gas mixtures (air and CO2, SF6, He) has shown an Uncertainty (C-m eas - C-true) of 2 percent over the full concentration range of of 0-100 pe rcent for. CO2 and SF6. The device is operable in the pressure range from - 50 to 100 kPa gage and in the temperature range from 0 degreesC to 40 degre esC. The instrument is rugged and will survive in noisy, turbulent environm ents. [S0889-504X(00)01202-2].