Rapid quenching by supersonic expansion and injection of water

Abstract

Gaseous components or gasborne particles in flows are often sensitive to mid range temperatures, whereby unintended side products or aggregated particles develop during cooling processes. Supersonic quenching combines high gasdynamic cooling rates of dT/dt<−10 6 K/s with a total enthalpy reduction through evaporation of an injected liquid. In this manner the residence time at critical temperatures is minimized. Up to now there are no publications covering this particular application. Preliminary test results regarding the massive water injection into a supersonic laval nozzle flow are presented as well as the developed supersonic quench concept and corresponding design rules. Essential is the suppression of an anew temperature rise downstream of the supersonic domain when the gas is compressed and decelerated again. Therefore liquid injection into the supersonic domain and its partial evaporation within it is a key feature. Despite the massive water injection the gas flow must remain in a supersonic regime. In addition to water injection from the wall a moveable slender cone equipped with water jets is extending into the divergent nozzle from the exit to enhance the coverage of the cross-sectional area with dispersed water. Presented experimental results in form of pressure and temperature profiles prove the functional efficiency of the supersonic quench. Pressure profiles attest the supersonic conditions downstream of the water injection and define the supersonic domain length. Two dimensional temperature plots demonstrate the sufficient water distribution, the suppression of hot subsonic zones and the total evaporation of the injected water within the quench domain. Applied to “Gasdynamically induced nanoparticle synthesis” spherical non-aggregated nanoparticles are obtained.