A variety of visualization techniques such as shadowgraph, Shlieren and holographic interferometry, are applied to visualize thermo-fluid phenomena in cryogenic fluids, superfluid helium (HeII) and supercritical nitrogen. This paper describes the phenomena revealed and images visualized in cryogenic fluids using those visualization techniques.
Visualization techniques compatible with low temperature environment are essential in the extension of room temperature techniques to the study of cryogenic flows. Focusing on two-phase fluids, this paper describes several optical tools developed in severe environments (high magnetic field, superfluid flows,...) to access two-phase patterns (meniscus shape, bubbles and droplets, stratified two-phase flows...).
The particle image velocimetry (PIV) technique was successfully applied for measuring the velocity of a He II thermal counterflow jet. Neutrally buoyant hydrogen-deuterium solid particles were used as tracer particles for PIV measurement. In the application, the normal component velocity was measured. The jet velocity profile and spatial decay of the jet velocity were compared with those of round jets of ordinary viscous fluids. The velocity that was measured near the jet nozzle was compared with the theoretical prediction.
A study on visualization of superheated He II —superheated He I interface in a narrow channel between parallel walls as a result of heating was investigated using a shadowgraph method. It was confirmed that a superheated state was readily created in the narrow channel that simulates cooling channels of superconducting magnets. Superheated He II-superheated He I interface transiently appeared above 2.0 K up to lambda temperature when applying small heat flux. The boiling accompanying with superheated He II- superheated He I interface that was repeatedly generated and collapsed was found to have a high heat transfer coefficient.
We report an experimental approach for applying the PIV technique to measurements in He II forced flow. The forced flow of He II is created in a 3.5 m long experimental channel within the Liquid Helium Flow Visualization Facility (LHFVF). We demonstrate that micron size solid hydrogen isotope particles are the best choice for tracing He II forced flow. A novel particle seeding device has been developed to form and seed such solid hydrogen isotope particles directly within He II flow. Velocity field measurements of forced flow He II subjected to a constant locally applied heat flux are presented. Results are compared to analysis based on the two-fluid model.
Measurement techniques have been developed to characterize form shell targets for the Fast Iginition Realization Experiment (FIREX) project. Interferometry has been adopted to determine the volume of hydrogen fuel in the form shell. A preliminary experiment has been conducted to evaluate the aplicability of interferometry. The paper describes the measurement techniques and discuesses its accuracies.