MEMS sensor measurement of surface temperature response during subcooled flow boiling in a rectangular flow channel

• A MEMS temperature sensor was used to study subcooled flow boiling of water at 1 bar.
• The measured surface temperature showed basic heat transfer phenomena under a bubble.
• Evaporation and dry-out of a microlayer and rewetting of a dry patch were observed.
• A microlayer evaporated in <~1 ms and the surface temperature dropped by 10 oC.
• The rewetting caused small and fast temperature drop in the bubble departure process.

Subcooled flow boiling experiments have been conducted using water at atmospheric pressure in a rectangular flow channel. These experiments are conducted in support of a US DOE Nuclear HUB project, the Consortium for Advanced Simulation of Light Water Reactors (CASL). CASL aims at the development of an environment for predictive simulation of light water reactors, and subcooled flow boiling is investigated experimentally in order to develop and validate 3-D Interface Tracking Models (ITMs). In the present experiments, a MEMS sensor has been used to obtain wall temperature response during nucleation, growth and departure of a vapor bubble in subcooled water flowing upward through a vertical rectangular test section. High-speed video images and MEMS sensor data collected at 5000 fps and 50 kHz, respectively, revealed rapid microlayer evaporation, dryout and rewetting phenomena under a single vapor bubble following nucleation accompanied by rapid wall temperature changes of up to ∼10 K.