Study on cryogenic liquid boiling

Experimental investigations of heat transfer and microcharacteristics during boiling of hydrogen, nitrogen and oxygen on tubular heaters 100 mm long have been carried out. Nitrogen and oxygen were filmed on a 8 mm dia. tube in the pressure ranges of 0.22 to 4 bar and 0.1 to 8 bar, respectively, hydrogen on a 5 mm tube at 0.072-2 bar. The study of internal characteristics of heat transfer and crises during bubble boiling of cryogenic liquids shows that the pressure effect on boiling characteristics has different character at high and low temperatures. The borderline between ''high'' and ''low'' pressures (Psub(bord.) approximately 0.1 Psub(k)) is determined by conditions of growth and separation of vapor bubbles (quasi-static and dynamic conditions, respectively) and can be estimated by comparing the surface tension forces and inertial liquid reaction forces affecting the vapor bubble. For the cryogenic liquids, the separation of vapor bubbles at high pressures (in the quasi-static conditions) occurs from the microcavity edge where the bubble is formed, and the Fritz formula for the calculation of the separation bubble radius is of no use