Measurement of critical heat flux for narrow annuli submerged in saturated water

An experimental study has been performed to improve understanding of boiling phenomena and critical heat flux (CHF) in narrow gaps. The experiment has been performed with annular test sections submerged in a pool of saturated water under atmospheric pressure with the following conditions: outer diameter of inner tube of 19 mm; heated length of 200 mm; annular gap sizes of 0.5-3.5 mm, and inclination angles from horizontal to vertical positions. The experimental results reveal that the CHF increases with the gap size and the inclination angle. A one-dimensional two-phase model with a modified friction factor correlation is suggested to predict the CHF condition. The developed model is also compared with other CHF data.