Marco La Mantia

Visualization of two-fluid flows of superfluid helium-4

Cryogenic flow visualization techniques have been proved in recent years to be a very powerful experimental method to study superfluid turbulence. Micron-sized solid particles and metastable helium molecules are specifically being used to investigate in detail the dynamics of quantum flows. These studies belong to a well-established, interdisciplinary line of inquiry that focuses on the deeper understanding of turbulence, one of the open problem of modern physics, relevant to many research fields, ranging from fluid mechanics to cosmology. Progress made to date is discussed, to highlight its relevance to a wider scientific community, and future directions are outlined. The latter include, e.g., detailed studies of normal-fluid turbulence, dissipative mechanisms, and unsteady/oscillatory flows.

Particle trajectories in thermal counterflow of superfluid helium in a wide channel of square cross section

The motion of micrometer-sized solid hydrogen particles in thermal counterflow of superfluid helium is studied experimentally by using the particle tracking velocimetry technique. The investigated quantum flow occurs in a square channel of 25 mm sides and 100 mm length, appreciably wider than those employed in previous related experiments. Flow velocities up to 10 mm/s are obtained, corresponding to temperatures between about 1.3 K and 2.1 K, and applied heat fluxes between ca. 50 W/m2 and 500 W/m2. The character of the obtained particle trajectories changes significantly as the imposed mean flow velocity increases. At thermal counterflow velocities lower than approximately 1 mm/s, the particle tracks appear straighter than at larger velocities. On the basis of the current understanding of the underlying physics, it is argued that the outcome is most likely due to the transition to the turbulent state of the investigated flow as, for narrower channels, this transition was reported to occur at larger veloc...

New experimental set-up to analyse cryogenic flows by visualisation

The first laboratory in Europe for visualisation of liquid helium flows is currently being established at the Charles University in Prague. The use of such a valuable experimental approach for the analysis of cryogenic flows of normal and superfluid 4He is introduced and its specific features discussed. More importantly, it is shown that the newly implemented flow visualisation equipment is potentially capable of obtaining novel results, i.e. further understanding of the involved physics.

Novel experimental apparatus to visualise low-temperature flows

The first laboratory in Europe for the visualisation of liquid helium flows is currently being established at the Charles University in Prague. The use of such a valuable experimental tool for the analysis of cryogenic flows of normal and superfluid 4He is introduced and its specific features discussed. More importantly, it is shown that the newly implemented flow visualisation equipment is potentially capable of obtaining new results, that is, further understanding of the underlying physics.