Vapor-liquid two-pase flow.

Flow and heat transfer in boiling two-phase nitrogen flow.


 The Japan Aerospace Exploration Agency (JAXA) is moving forward with the development of the technology for hypersonic pre-cooled turbojet engines that is fueled by liquid hydrogen. Because the liquid hydrogen is in a forced convection boiling heat transfer state (vapor-liquid two-phase flow) as it undergoes heat transfer with high-temperature air in the air pre-cooler during high-speed flight, pressure drop and heat transfer performance are important from a design standpoint.

 As for our proposing high-efficiency hydrogen energy system, heat inleak during pipeline transportation or heat generation induced by quenching of superconducting equipment would cause liquid or slush hydrogen to a forced convection boiling heat transfer state.

 Accordingly, experimental studies of flow patterns, void fraction measurement, pressure drop, and heat transfer were performed on boiling liquid nitrogen flow with respect to circular pipe with an inner diameter of 10 or 15 mm, square pipe with sides of 12 mm, and equilateral triangular pipe with sides of 20 mm, at each heat flux of 5, 10 and 20 kW/m2 [26, 27].

 The above figure shows six flow patterns consisting of bubbly, plug, slug, slug-annular, wavy-annular, and wavy flows observed for a circular pipe with an inner diameter of 15 mm.

 Part of the work is carried out in collaboration with JAXA.