Numerical simulation of bubble behaviors in subcooled flow boiling under swing motion

A numerical investigation of bubble behaviors in subcooled flow boiling of water under the effect of additional inertial forces has been performed considering energy and mass transfer during phase change based on the VOF (volume-of-fluid) method. The pressure ranges from 0.1 to 1.0 MPa, and heat flux from 200 to 500 kW/m2. The mass flow rate and inlet subcooling are specified at 320 kg/m2 s and 10 K, respectively. The liquid–vapor interface is captured using the piecewise linearity interpolation calculation (PLIC) geometry restructuring method. The simulations are carried out on upward water flow in a vertical, rectangular duct with single side heating surface. The pressure, velocity vector and temperature distribution around two isolated bubbles are studied firstly. The behaviors of bubble coalescence, sliding, detachment from the heated wall, and the bubble shape variation during lifetime are further examined. The bubble behaviors in the different pressure and heat flux are investigated. The simulated results of bubble growth rate and wall temperature are agreed well with the correlations in the literatures. The additional inertial forces caused by swing are negligible, but the fluctuation of mass flow rate caused by swing motion influences the forces acting on bubble significantly. Compared with the motionless condition, the pressure drop is increased and the fluctuation becomes acute as heat flux increases under the swing condition.

► Secondary flow exists inside bubbles due to the evaporation and condensation.
► The relative motion of these two bubbles generates two symmetrical vortexes and a stagnant region.
► The supplementary microlayer between the two coalescing bubbles is observed in the simulation.
► The additional inertia forces generated by swing are negligible.
► The fluctuation of mass flow rate caused by swing motion effects the Fsl, Fqs, Fh and the phase distribution significantly.