Fabrication and characterization of a micro-boiling meter for heat transfer measurements on a single nucleation site

Abstract

Accurate characterization of heat transfer during pool boiling requires sensors capable of resolving rapid transients and highly localized thermal events. Conventional approaches often suffer from limited spatial resolution and slow thermal response due to intermediate material layers. To overcome these limitations and obtain accurate measurements of surface temperature and heat flux during pool boiling studies, we used a boiling meter. Two of these consist of commercially available sensors. To improve the study of vapor bubble dynamics, a third boiling meter was designed, dimensioned, and microfabricated. It was fabricated on a Borofloat 33-silicon composite substrate featuring a suspended Borofloat membrane with a central 200 $μ$m micropillar and a laser-ablated nucleation site (100 $μ$m x 115 $μ$m). Two platinum resistance temperature detectors (Pt-RTDs) were integrated on both sides of the substrate to enable direct, localized, and time-resolved measurements of wall temperature and heat flux during bubble formation. Characterization of the microfabricated boiling meter was carried out in controlled radiative environment and in pool boiling. The microfabricated device exhibited a thermal characteristic time of around 200 ms in radiative tests (more than 30 times shorter under similar operating conditions than the times found with boiling meters composed of commercial sensors), but was able to capture a bubble frequency of 26 Hz, which validates its ability to resolve transient thermal events. Its suspended glass-membrane structure, combined with the direct liquid-RTD interface, provides both high temporal resolution and spatial sensitivity, essential for capturing the short timescales of bubble nucleation, growth, and departure.