Mass Transfer: Printed Circuit Board (PCB) Submerge Cooling

Description

This research presents a numerical investigation of the fluid dynamics and heat transfer in a two-phase immersion (submerged) cooling system. The subject of the study is a set of chips with interposer components mounted vertically on a printed circuit board (PCB), submerged in the dielectric coolant HydroFluoroEther (HFE)-7100. The main objective is to understand how the physical architecture and geometry of these components influence the flow paths of bubbles, the phenomenon of bubble coalescence, and the extent of vapor coverage on the chip surfaces.

The geometry was created in SpaceClaim, ensuring an accurate representation of the PCB and its components. A structured mesh was generated in ANSYS Meshing, comprising more than 19,000 elements to enable reliable numerical simulation of this configuration.

A transient solver was used, since the problem requires tracking changes in the volume fraction of the two phases over time. Gravity was included in the model, fixed at −9.81 m/s² in the Y direction.

Methodology

The PCB was modeled in ANSYS Fluent. The evaporation and condensation mass transfer mechanisms were captured using a multiphase VOF (Volume of Fluid) model, which resolves the interface between the liquid coolant and the vapor phase as boiling occurs. The dielectric coolant was assigned a saturation temperature of 339 K. The turbulent flow was solved using the standard k-epsilon model together with the energy equation, allowing the temperature distribution throughout the domain to be computed.

Conclusion

The study examines the fluid dynamics and heat transfer in a two-phase immersion cooling system featuring vertically mounted chips and an interposer component. Using a computational model based on the finite volume method and the VOF approach, it investigates how the interposer component affects the deflection of bubble streamlines, the coalescence of bubbles on the heated chips, and the overall cooling rate.

The results show that the interposer component can significantly influence chip heat transfer, with the evaporation–condensation mass transfer at the phase interface governing how heat is removed from the chip surfaces. The work highlights the importance of electronic system topology in the efficiency of two-phase cooling and offers valuable guidance for designing electronic systems that achieve effective thermal management.