Critical Heat Flux During Natural Circulation Boiling of Saturated Liquid in Annulus With Uniformly Heated Outer Tube

Critical heat flux has been measured during natural circulation boiling of water and R113 on a uniformly heated outer tube in a vertical annular tube. The experiment was carried out using water at atmospheric pressure and R113 at a pressure of 0.1--0.4 MPa for the annular gap width of S = 1.0--4.0 mm, the heated tube diameter of 9--17 mm, and the annular tube length of 100--1,000 mm. The similarity of critical heat flux between annular configurations of either inner or outer heated tubes and a simple heated tube can be clearly elucidated based on the characteristics of the heated equivalent diameter. The critical heat flux measured for S = 1 mm can be predicted accurately by existing correlation for the annular tube and for clearance larger than S = 4 mm by existing correlation for the single tube. A new correlation for medium clearances from S = 1 to 4 mm has been developed to connect between both the existing correlations.