Flow Boiling in Microchannels Coupled with Surfaces Structured with Microcavities

This study addresses the characterization of two-phase flow phenomena in a microchannel heat sink designed to cool high-concentration photovoltaic cells. Two-phase flows can introduce instabilities that affect heat exchange efficiency, a challenge intensified by the small dimensions of microchannels. A single polydimethylsiloxane (PDMS) microchannel was fixed on a stainless steel sheet, heated by the Joule effect, which was cooled by the working fluid HFE 7100 as it undergoes phase change. Experiments were performed using two microchannel widths with a fixed height and length, testing two heat fluxes and three values of the Reynolds number, within the laminar flow regime. Temperature and pressure drop data were collected alongside high-speed and time- and space-resolved thermal images, enabling the observation of flow boiling patterns and the identification of instabilities. Enhanced surfaces with microcavities depict a positive effect of a regular pattern of microcavities on the surface, increasing the heat transfer coefficient by 34–279% and promoting a more stable flow with decreased pressure losses.