Annular two-phase flow behavior in rod bundle with spacer

The major results and findings regarding the liquid film and droplets' behavior are summarized as follows: (1) The singlet disturbance-crests are formed near the inlet. A mechanism for this process based on the turbulent characteristic of the gas flow was proposed. This crest can return to the liquid film or undergo an entrainment processes to create the first droplets in the system. (2) Entrainment phenomena occur under the bag break-up, ligament break-up and impingement mechanisms. The first two processes can happen at the singlet disturbance-crests as well as the disturbance waves. After the generation, the initial velocities of droplets are higher than the main wave structures. The droplet impingement can occur at the surface of any kind of wave and the amount of the liquid ejected in the form of secondary droplets may be significant. (3) The disturbance waves are accompanied by multiple entrainment processes. The similarities between these processes and the entrainment events occurring at the singlet disturbance-crests suggested that the singlet disturbance-crest could be the first form of the disturbance waves. (4) At upstream of the spacer, the droplet's population and size distribution directly relate to the magnitude of waves existing on the liquid films because most of them are generated through the entrainment processes. (5) The spacer generates a huge number of small-size droplets and, in the case of low gas superficial velocity, several droplets whose diameters exceed the maximum droplet diameter at upstream. (6) The asymmetrical spatial distribution of the droplets at downstream of the spacer quantitatively emphasizes the important contribution of the droplet impingement processes to the liquid entrainment phenomena. (J.P.N.)