Flow patterns and hydrodynamic model for gas-liquid co-current downward flow through an orifice plate

Gas-liquid co-current downward flow through an orifice plate was experimentally investigated, in which the surface tension, gravity, gas-liquid interface friction force and fluid inertial force may have comparable effects on the flow of the liquid. In experiments, nine orifice plates with different hole-diameter and thickness were used, the gas superficial mass flux changes from 1.7 to 41.4 kg/m2/s and the liquid superficial mass flux is from 38.7 to 295.3 kg/m2/s. Four flow patterns, namely, trickling, continuous, semi-dispersed and perfect-dispersed flow were identified by means of observation. Flow pattern maps were plotted using gas superficial mass flux vs. liquid superficial mass flux, and the transition mechanism of different flow patterns and the influence of the hole-diameter on the transition boundaries were discussed. Also, a statistical parameter was used to assist in understanding the transition mechanism from trickling/continuous flow to semi-dispersed flow. Next, by considering the interaction between gas and liquid, a model about the film thickness around orifice rim was proposed and the factors influencing the liquid film thickness were discussed. These discussions and the comparisons with the film thickness in the case of gas-liquid annular flow in pipe show that the model is very effective. Based on this model, an equivalent length model for the orifice friction was developed to predict the pressure loss of gas-liquid two-phase flow through the orifice, and satisfactory agreement with experimental data was obtained. In addition, by using the equivalent length method, a new correlation was proposed to successfully predict the pressure loss of single gas phase flow through the orifice plate.