Flow boiling of R1336mzz(Z) in tapered microgaps with asymmetric dual-V microchannels

The development of high heat flux cooling technologies has attracted great interest of investigations during the last decades, which motivated a series of investigations regarding flow boiling in microchannels. In a recent investigation, new heat sinks composed of a bottom surface milled with asymmetric Dual-V microchannels combined with a tapered microgap were presented, and the occurrence of boiling inversion was documented for the first time in flow boiling experiments using water as working fluid. It is noteworthy, however, that despite its great thermal properties the use of water as working fluid may not meet some cooling requirements, and the use of refrigerants is necessary. In addition, with the increasing concerns with environmental impacts, novel re-frigerants with low environmental impacts have been presented to the market, but limited results are found in the literature for their flow boiling performances. Hence, the present work is focused on flow boiling experiments with the Hydro-Fluoroolefin R1336mzz(Z) in copper heat sinks combined to a tapered manifold. Tests were conducted using three different surfaces, with and without asymmetric Dual-V microchannels, the selected saturation temperature was 41 degrees C, and inlet mass fluxes varied from 400 to 1000 kg/m2s. Effects of various parameters were evaluated and put in context to the flow patterns observed with a high-speed camera. The best surface promoted the dissipation of up to 93 W/cm2 without reaching the critical heat flux, with wall temper-ature lower than 74 degrees C, pressure drop lower than 10 kPa, and maximum heat transfer coefficient reaching 22 kW/m2K.