The implementation of a three-field model into TRAC-M/F90 and its application to annular-mist flow

A three-field model was developed and implemented into the one-dimensional components of TRAC-M/F90 version 3782 for a better estimation of entrainment phenomena. The divide and conquer algorithmic technique was adjusted for the implementation after considering the verifications. The governing equations were composed of the conservation equations of each field with thermal-equilibrium assumption between the two liquid fields. In the development of the momentum equation for an entrained droplet, two different kinds of approaches were tested: the simple force balance on a single droplet and the field-type equation based on the continuum assumption. The first showed unstable nature and the latter was chosen. All of the necessary empirical correlations were obtained from literature, in particular the physical models of COBRA-TF. The sensitivities of each empirical correlation were investigated where the effect of droplet diameter and droplet drag was found to be negligible. The advantages of the SETS numerical scheme in comparison with the semi-implicit numerical scheme were addressed in the simulation time and the maximum allowed time-step size. Finally, the simulations of Collier and Hewitt's experiment and Wuertz' experiment were performed. In the simulations of Collier and Hewitt's experiment, the RMS error of entrained liquid flow rate and pressure gradient were 16.5 and 9.6%, respectively. In Wuertz' experiment, the predicted values agree with the measured ones with the RMS error of 2.8% in entrained liquid flow rate. (author)