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International Heat Transfer Conference 7

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

CHF IN HIGH-PRESSURE REGIME FOR FORCED CONVECTION BOILING IN UNIFORMLY HEATED VERTICAL TUBES OF LOW LENGTH-TO-DIAMETER RATIO

Yoshiro Katto
Department of Mechanical Engineering, Nihon University Kanda-Surugadai, University of Tokyo, Chiyoda-ku, Tokyo 101, Japan

S. Ashida
Department of Mechanical Engineering, University of Tokyo Bunkyo-ku, Tokyo, Japan

DOI: 10.1615/IHTC7.1100
pages 291-296

Abstract

An experimental study is attempted on the critical heat flux (CHF) of flow boiling of R-12 in a 5-mm dia. tube under somewhat particular conditions of vapor/liquid density ratios pv/ pz = 0.305− 0.109 and a length-to-diameter ratio l/d = 50 such as encountered in the studies of helium boiling. The mass velocity G ranges from 700 to 7000 kg/m2s and the inlet subcooling enthalpy ΔHi from 0 to 40 kJ/kg. Anomalous, upstream CHF is observed at high pressures in a limited range of low inlet subcooling when the mass velocity is very high. As for the CHF of regular type originating CHF conditions at the exit end of heated tube, the data obtained suggest the availability of both generalized correlations recently proposed by Katto and by Shah, but further studies are needed, particularly on the criterion for the onset of high-pressure regime in the range of low length-to-diameter ratios.

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