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International Symposium on Heat and Mass Transfer in Refrigeration and Cryogenics
September, 1-5, 1986, Dubrovnik, Yugoslavia

DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo


ISBN Print: 978-3-54017-957-3

Heat Transfer at Boiling of Nitrogen under Subatmospheric Pressure and Its Intensification

pages 547-552
DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo.360
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SINOPSIS

The basic characteristics of vaporization change essentially at a decrease of the pressure below atmospheric, as it is given in /1-3, etc./. The break-away diameter of the bubble increases greatly, the break-away frequency reduces, the "idle" time of the vaporization centers increases, and the quantity of operating centers reduces. At a pressure close to the triple point the process of vaporization gains an unstable, explosive character. In the final end, the intensity of heat exchange and the displacement of the beginning of steady boiling toward the region of high temperature heads reduces greatly. As a result, the problem arises in many practical cases of stabilization and intensification of the vaporization process.
Research was carried out with nitrogen boiling on the external surface of an aluminium pipe with a diameter of 16 mm and a length of 100 mm. The pipe was heated by an electric heater embedded in magnesium oxide inside the pipe. The temperature of the pipe wall was measured by copper-copel thermocouples. The experiments were carried out in a vessel that was placed in a cryostat with vacuum-layered insulation and nitrogen cooling of the internal wall, perceiving the heat flows from the ambient medium. The cryostat was furnished with sight glasses for visual observation of the beginning and the character of vaporization.

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