Flow boiling of dielectric fluid HFE – 7000 in a minichannel with pin fin structured surfaces

Flow boiling of dielectric fluids in minichannels provides promising cooling alternatives for achieving high heat flux cooling. In this regard, flow boiling experiments in minichannels with six different surface characteristics were performed using HFE – 7000 as the working fluid. Average boiling heat transfer coefficients were obtained over effective heat fluxes ranging from 50 to 1300 kW/m² and mass fluxes from 125 to 280 kg/m²s. The effects of the presence of elliptical pin fins, presence of distribution pin fins as well as tip clearance were assessed, and different flow patterns could be identified: single – phase flow, bubbly flow, intermittent flow, and annular flow. The results indicate that elliptical pin fins significantly augmented the flow boiling performance. Moreover, the distribution pin fins in the inlet region could provide more homogenous flow distribution and results in enhanced heat transfer. Additionally, the positive effect of tip clearance could be observed for its low (<5%) values.