• Pool Boiling
• Microgravity
• Microstructured Surfaces
• Heat Transfer Enhancement
• Electric Field

Pool boiling heat transfer is used in many industrial processes, including electronics cooling, power generation, and two-phase thermal management in space stations and nuclear plants. Critical Heat Flux (CHF) is an important performance limiting
condition. In particular, in micro-g, CHF encounters a drastic reduction. Thus, it is important to understand the mechanisms that lead to this and identify ways to enhance it. In this work, we explored the possibility to enhance CHF combining engineered surfaces (passive technique) and electric field (active technique).
In normal gravity, it has been demonstrated that CHF is enhanced with microstructures; this is thanks to rewetting due to sloshing and imbibition, which is independent of gravity. Moreover, electric field creates a driving force able to remove vapor from the surface. Their combined application appears an effective way to prevent dryout, even if the two effects influence each other. Experiments were run during the 71th PFC held by ESA. A dedicated apparatus was built and operated with bare and microstructured surfaces, using subcooled FC72 at 1 bar. A DC electric field was applied via a metal grid laid 6 mm over the surface. Results showed that CHF reduced in micro-g, but these enhancement techniques are able to deal with this reduction: respected to standard g, electric field effects are more effective, working as buoyancy, while microstructures enhancement decreases due to the lack of sloshing, dependent on gravity.