Heat transfer near critical conditions in two-phase thermosiphon flow configuration with boiling helium has been investigated. The experiment was made at the steady-state conditions in a 14 mm diameter vertical copper tube, uniformly heated over a length of 1.2 m. Transition from the nucleate boiling to the film boiling regime and critical heat flux are measured at five locations along the heated tube. Critical heat flux are predicted within 30% by the Katto’s and Sha’s correlation for two-phase forced flow and within 20% by the Lehongre’s correlation specific to natural boiling helium excepted for low value of L/D. |
