Experimental results on two-phase He I natural convection flow, i.e. thermosiphon
open flow, for a vertical copper tube (14 mm inner diameter) uniformly heated over
a length of 1.2 m are presented. Maximum total mass flow rate of 22 g/s and exiting
vapor quality factor of 0.2 have been achieved in the steady state regime for a heat
flux up to 2000 W/m² near atmospheric pressure. In addition, wall temperature difference
are measured and critical heat flux and heat transfer coefficients are presented as a
function of heat flux. In the nucleate boiling regime, heat transfert coefficient
correlations, based on the Martinelli parameter, are proposed for different tube height.
They described the data within 20% error margin in the range of 2 1.e5 Reynolds number.
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