Four film boiling modes including the silent film boiling and the noisy film boiling were discriminated experimentally. Each mode was classified through visual observation and transient pressure and temperature measurements near the heater. It was found that in subcooled He II there were two film boiling modes, which are the strongly subcooled and weakly subcooled film boiling modes. The variation of boiling state between these two modes could be visually observed well by use of a transparent heater. All mode of film boiling is clearly mapped in diagrams as a function of pressure, temperature and heat flux. It is elucidated that the existence of He I layer influences the development of the vapor layer. (Translation of the article originally published in Cryogenics 49 (2009) 583-588
Synopsis::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 IIsuperheated 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.
Synopsis: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.
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