Relationship between high quality CHF and boiling length in annulus geometry with uniformly heated rod

The relationship between the boiling length and the CHF in annulus geometry with uniformly heated rod has been studied. In this study the CHF data under pressure of 0.57∼15.01 MPa, flow rate of 200∼650 kg/m2s, inlet subcooling of 85∼353 kJ/kg and exit quality of 0.106∼0.536 have been applied. As a result of examining the flow pattern over the heated section, all of the CHF data were the dryout type CHF in annular flow and the locations of the churn to annular flow transition moved down stream of the heated section with increasing the pressure. The effect of pressure on the boiling length under the CHF conditions showed the trends similar to the effect of pressure on the CHF. The relationship between the non-dimensional CHF, q CHF and mass flux taking into account of the boiling length, G ( Lh/ LB) indicated the linear relationship without scatter and regardless of pressure and inlet subcooling. The CHF calculated by using the relationship between the non-dimensionless CHF, q CHF and mass flux, G ( Lh/ LB) predicted very well the experimental CHF data with the pressure dependence