Theoretical investigation on dryout point of upward annular flow in narrow gap with bilateral heating

Based on the separated flow model, a theoretical three-fluid model predicting for dryout point of annular upward flow in a vertical narrow annuli with bilateral heating has been developed in the this paper. The predicted results agree well with the experimental data. The numerical results show that: a) when the dryout point occurs on the inner tube, critical quality will increase with decreasing the curvature of tube and gap size for a fixed heat flux of outer tube. When the dryout point occurs on the outer tube, the case is reverse for a fixed heat flux of inner tube; b) the influences of pressure and mass flow rate on critical quality is very slight when the gap size is smaller than 0.5 mm or the outer diameter of inner tube is larger than 20 mm with a fixed gap size.