Experimental Investigation of Flow Boiling in a Single, Surface-Augmented Silicon Microchannel

Advances in electronics such as chip level integration and die stacking have led to a bottleneck in further development since dissipation of the resulting high heat fluxes continues to be a challenge. Ongoing research in the field of flow boiling to meet the rising demands has resulted in the evolution of potential cooling technologies such as microchannel heat sinks. In an effort to understand the flow boiling in these micro-structures, experiments were previously conducted by the authors using 19 parallel, surface enhanced microchannels with a hydraulic diameter of 253μm. Flow instabilities which can be attributed to channel-to-channel interaction and the effect of compressible volumes at channel exit and inlet were observed under certain subcooled boiling conditions although these were mitigated in saturated conditions by the presence of re-entrant cavities. To completely eliminate the instabilities, it is important to identify the underlying mechanisms by isolating these causes. To achieve this, a study of flow boiling of dielectric fluid FC72 (C₆F₁₄) in a single microchannel test section of height 347 microns and width ranging from 100–400 microns was conducted. The base of the microchannel was augmented with reentrant cavities. The study was performed at mass fluxes ranging from 500–2000 kg/m²-s and inlet subcooling up to 20°C. The results include the parametric effects of inlet subcooling, mass flux, heat flux and number of cavities on the pressure drop. It was observed that the pressure drop oscillations in the subcooled boiling regime observed earlier in the multichannel configuration, were not observed in the subcooled regime in the single channel test device of width 100 microns. Further, adiabatic experiments were conducted to study the effect of channel size on the friction factor. These studies will help provide fundamental design input to enable the development of microchannel heat sinks.