EXPERIMENTAL TECHNIQUES

Pulsed CRESU – de Laval nozzles

An experimental system for the production in a vacuum chamber of a uniform gas jet by supersonic expansion through a Laval nozzle at very low temperature (T = 11.7 – 177.5 K). This is the most powerful pulsed CRESU worldwide, achieving the lowest temperature ever, 11.7 K. More details in Jiménez et al., Rev. Sci. Instrum. 86: 045108 (2015) 1.

View of the CRESU system

Pulsed gas expansion system inside the CRESU chamber: 1. Reservoir; 2. Rotary disk; 3. Exit of the Laval nozzle; 4. Optocoupler.

Laval nozzle: 1. View of the divergent exit. 2. Convergent and divergent side view.

Pitot tube system

This system is placed inside the CRESU chamber in separate experiments when the supersonic flow needs to be aerodynamically characterized. In this system, the impact pressure is measured as a function of the exit of the Laval nozzle by a fast pressure transducer. From the measured impact pressures (P_i), the temperature of the gas jet (T₁), and the length of uniformity (d) are determined.

Schematics of the fundamentals of the impact pressure measurement with a Pitot tube. M is the Mach number and d=0 the exit of the Laval nozzle.

Photograph of the Pitot tube system: 1. Translational platform; 2. Fast pressure transducer; 3. Micrometers screws; 4. Exit of the Laval nozzle; 5. Optocoupler; 6. Rotary disk.