Subcooled boiling critical heat flux in annuli at lower pressure

Subcooled boiling CHF experiments have been carried out in annuli with outer diameter of 12, 32 and 70 mm and gap width of 2 to 4 mm, covering the range of pressure of 0.17 - 1.8 MPa, mass flux of 1.3 to 18.2 g/m2s, outlet subcooling of 26-105 K and critical heat flux of 0.24 - 1.8 x 107 w/m2. The gap width and pressure do not exhibit appreciable effects on the CHF. 578 CHF data are simply formulated as a function of water subcooling and velocity with AVG of -0.01 and RMS of 0.083. The results are compared with the calculations of Knoebel correlation, Gambill correlation, Sudo correlation and CHF Look-up table. Among them the Knoebel correlation gives the best prediction. The comparison between the CHF data of tube of D=8 mm and annuli evidences some relation of the geometry effect to the flow rate. (author)