Numerical investigation on the dryout point of annular flow in the upward narrow annuli with bilateral heating

Based on the fundamental conservation principles -the mass, momentum, and energy conservation equations of liquid films and the momentum conservation equation of vapor core, a theoretical three-fluid model has been developed to predict the dryout point of upward annular flow in vertical narrow annuli with bilateral heating. The range of the parameters are: pressure from 0.5 to 5.0 MPa; mass flow rate from 30 to 150 kg/(m²•s); gap size from 1.2 to 2.0 mm. Through numerically solving the model, the relationships among the parameters of the critical quality (X _C), critical heat flux (Q _CHF), mass flow rate, system pressure, and the ratio of heat flux on the inner wall of the outer tube to that on the outer wall of the inner tube (q _o/q _i) are obtained and analyzed. The predicted results accurately match with the experimental data. For a fixed q _o, X _C will increase with the decreases in the gap size and the tube curvature when the dryout point occurs on the outer wall of the inner tube. However, for a fixed q _i, when the dryout point occurs on the inner wall of the outer tube, the parametric trend is reverse. When the dryout point on the inner and outer walls occur simultaneously, X _C reaches a peak value, and the ratio of q _o/q _i at this position changes with the gap size and the tube curvature.