Numerical Simulation of Annular Flow boiling in Millimeter-scale Channels and Investigation of Design Parameters Using Taguchi Method

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As the technology progresses, the electronic components become smaller and at the same time continue to produce more heat, and therefore development of new high heat-flux cooling technologies have become obligatory. The mini and millimeter-scale phase change cooling systems, which have a reduced size and a large surface area where heat transfer can take place, have become an integral part of advanced cooling systems. When comparing phase-change cooling systems with other cooling systems, a relatively low flow rate of very high evaporation heat, which is associated with the phase change for most fluids, allows large amounts of heat to dissipate with flow boiling and substantially solves the many problems. The two-phase cooling technologies used for critical applications include; heat pipes, loop heat pipes and capillary pumped loops which are all passive hence very reliable solutions relying on only capillary effects. Though this passive device cannot meet future high cooling demands because of the limitations of the capillary pumping in terms of heat flux, transport distance and multiple heat source capabilities. On the other hand, in boiling and condensing flows functionality problems arise since at the micrometer and millimeter-scale, shear/pressure forces dominate over gravitational forces and cause thermally hydro-dynamically ineffective/problematic liquid-vapor configurations – such as plug/slugs flow regimes. For this reason, to overcome the requirement of large amounts of heat transfer from limited spaces and resolving the above problem, novel millimeter-scale phase-change devices should be developed. In this study, for the design of millimeter-scale boilers a 3D Ansys-Fluent© simulation model was developed and numerical simulations were conducted for two different cooling fluids (water and FC-72), different mass flow rates and two different channel heights. Moreover, to examine the simulation results Taguchi method was used. In order to realize thin film annular flow over the boiler surface, employed specific boundary conditions in the 3D simulation model were obtained by means of one dimensional Matlab© simulation code. By means of utilizing the evaluated numerical results, distribution of heat transfer coefficient, vapor quality and pressure drop over the heat transfer surfaces were reported.