Our laboratory was the first one in Europe to visualize cryogenic flows of liquid helium. We employ the Particle tracking velocimetry technique (PTV), based on the tracking of micron-sized particles, dispersed in normal liquid or superfluid helium, and illuminated by a laser sheet. The motions of the particles witrin the flow is captured by a fast camera. Computer post-processing of the acquired images allows us to get access to time-resolved trajectories of individual particles, as well as other kinematic quantities (velocity, acceleration, etc.).
Visualization of thermal counterfow in superfluid 4He (temperature of the helium bath 1.66 K). Micron-sized solid deuterium particles are employed as tracking particles. The flow is driven by a planar heater located below the camera field of view, supplying the heat flux of ca. 500 W/m2.
Visualization of the flow driven by a transparent oscillating obstacle, in superfluid 4He, at termperature 1.24 K. Again, micron-sized solid deuterium particles are employed.
Visualization of what is the most likely a reconnection of two quantized vortex lines in superfluid helium, at 1.5 K. The vortices are decorated with micron-sized solid deuterium particles.
