The forced flow of dielectric liquids, undergoing phase change while flowing in a narrow channel formed between chips or a chip and a passive cover, is a promising candidate for the thermal management of high heat flux semiconductor devices. These microgap configurations provide direct contact — and hence highly efficient cooling — between a chemically-inert, dielectric liquid and the back surface of an active electronic component. However, the two-phase flow phenomena that establish the upper bound on the cooling capability of such microgap coolers are only poorly understood. In the present study, IR images of the heated surface of a two-phase microgap channel, 260 μm × 30 mm × 34mm, are obtained, through a sapphire window on the opposing wall of the channel Corrections are made for the reflection and absorption of IR radiation by the two-phase mixture flowing in the channel. Previously undetected spatial and temporal temperature variations, approaching 20 K, were observed on the surface of the microgap channel for heat fluxes of 3.2 W/cm2 and FC-72 mass flux of 35 kg/m2s. The frequency and amplitude of the observed temperature variations appear to reflect the complexity of the prevailing thermal transport phenomena and may provide evidence of local dryout in high quality annular flow in miniature channels.

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