Design and testing of temperature tunable de Laval nozzles for applications in gas‑phase reaction kinetics
Résumé
A series of three de Laval nozzles initiallydesigned to generate uniform supersonic flows in heliumat 23 and 36 K and in argon at 50 K have been used witheither pure nitrogen or mixtures of nitrogen with heliumor argon in order to make a sequence of pulsed supersonicflows working at different temperatures. For this, acomputer homemade program has been used to design deLaval nozzles contours for gas mixtures in order to determinethe theoretical pressure P and temperature T in thesesupersonic flows. Spatial evolution of T along the flow axisdownstream of the nozzle exit has been characterized witha fast response Pitot tube instrument newly developed.Twenty-eight different gas mixture conditions have beentested, indicating a very good agreement with the correspondingcalculated flow conditions. The length of uniformityΔL of the supersonic flows have been found to be>30 cm in more than 80 % of the situations and >50 cmfor more than 50 % of the tested conditions. Fine temperaturetunability was achieved in the range 22–107 K withvery small fluctuations of the mean temperature along ΔL.Advantages and limits of these new developments for studiesof gas-phase reaction kinetics are discussed.