The bubble leakage mechanism for vertical upflows by the phase separation concept

Recently, our research group proposed the phase separation condenser tube, in which a mesh cylinder was inserted to form the flow structure of “gas near the tube wall and liquid in the tube core”, significantly enhance the condensation heat transfer. But the bubble leakage towards the core region may worsen the heat transfer enhancement. In order to prevent the bubble leakage, the critical criterion was proposed based on the Young–Laplace equation, considering the inertia force, viscous force and pulsating flow. It was found that the critical criterion depends on the dimensionless parameter G ^*, the We number and a coefficient C. The numerical model was developed in terms of the volume of fluid method to predict the two-phase laminar flow in the phase separation condenser tube. The results show that the bubble leakage takes place at the bubble tip, which is agreed with the experimental observations. The critical curve distinguishing the non-bubble-breaking and bubble-breaking was obtained by comparing the bubble dynamics at different G* and We. The coefficient C was determined. The critical criterion for the bubble leakage is given as \( G^{*} \times We = \left( {0.22We^{0.99349} - \frac{{G^{*} }}{{4.7 \times 10^{3} \times We^{0.00651} }} + \frac{196.39}{{We^{0.00651} }}} \right) \times \frac{{4{ \cos }\alpha }}{\Delta \varTheta W} \) , providing the design and operation guidance for the phase separation condenser tube.