Numerical Study of Bubble Coalescence Heat Transfer During Nucleate Pool Boiling

ABSTRACT

Bubble growth during nucleate boiling in a large pool of liquid was modeled by numerically solving the unsteady Navier–Stokes laminar flow equations with the energy equation to predict the vapor and liquid flow fields. The analysis assumed two-phase, transient, three-dimensional, laminar flow with the Boussinesq approximation for the buoyancy. The volume of fluid method was used with the level set method to predict the bubble interface motion. The numerical investigations studied the dynamics and heat transfer rates associated with the coalescence of bubbles generated on two microheaters. The results for various wall superheats and liquid subcoolings illustrate the bubble growth and interaction dynamics throughout the coalescence process and the wall heat fluxes associated with the bubble nucleation and coalescence. In some cases, the bubble coalescence traps an evaporating liquid layer between the bubbles that then quickly evaporates, resulting in high heat fluxes. In other cases, the bubbles very quickly coalescence while the bubbles are still in the fast inertial controlled growth regime and the liquid layer between the bubbles is pushed out without evaporating, resulting in low heat fluxes as the surfaces are covered with vapor. These results show how similar conditions can lead to very different heat fluxes during coalescence as has been seen experimentally.

Acknowledgment

The authors thank Prof. Jungho Kim of the University of Maryland for his assistance in designing the heaters and the control systems.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China, Grant No. 50876050, the National Basic Research Program of China (No. 2011CB706904), and the Royal Academy of Engineering under the UK-China Industry Academia Partnership Programme scheme (UK-CIAPP\415).

Notes on contributors

Abdoulaye Coulibaly

Abdoulaye Coulibaly received his Ph.D. in Power Engineering and Engineering Thermophysics from Tsinghua University, Beijing, China in 2012. He is now a teacher at Ecole Normale Supérieure de Bamako, Mali. His research interests include boiling heat transfer.

Jingling Bi

Jingliang Bi received her Ph.D. in Thermal Engineering from Tsinghua University, Beijing, China in 2015. She is now an assistant researcher at the Nuclear Power Institute of China. Her research interests include heat and mass transfer during boiling and condensation, heat and mass transfer in microscale systems, and the thermal hydraulics of nuclear power systems. She has published numerous papers on heat and mass transfer during boiling.

David M. Christopher

David M. Christopher received his Ph.D. in Mechanical Engineering from Purdue University in 1982. He then taught in the United States for four years and has been at Tsinghua University, Beijing, China since 1991. He is now a full professor at Tsinghua University. His research interests include convection heat and mass transfer in microscale and microgravity systems, convection heat and mass transfer in two-phase systems, heat and mass transfer during boiling and condensation, and computational methods for convection heat and mass transfer. He has published numerous papers on heat and mass transfer in porous media, microscale systems, boiling heat transfer, and numerical methods for convection heat transfer applications.