Predicting velocity and motive mechanism of sliding bubble in vertical flow boiling

The motive characteristic of the sliding bubble was studied to constitute the reasonable mechanism models.The dynamic equation of the sliding bubble was established according to the analysis of the balance of forces acting on the sliding bubble in vertical flow boiling.The velocity of the sliding bubble was obtained,and the predicted results were compared with the experimental data of Maity.The predicted results of the model show that the velocity of the sliding bubble increases with extending time,but the increase of the sliding velocity of bubble decreases gradually.The velocity of the sliding bubble is higher than that of the bulk liquid when the sliding bubble lifts from the wall,which indicates that the drag force and add-mass force become the resistances from the driving forces to make the bubble slide along the wall.When the velocity of the sliding bubble is larger than that of the local liquid,the shear lift force pushes the sliding bubble against the wall,and the inertia of the liquid induced beneath the bubble due to the variation in the bubble shape probably makes the sliding bubble lift from the wall.