Time-resolved measurements of liquid–vapor thermal interactions throughout the full life-cycle of sliding bubbles at subcooled flow boiling conditions

• Published in: International journal of multiphase flow 2018-02, Vol.99 (C), p.94-110
• Main Authors: Estrada-Pérez, Carlos E., Hassan, Yassin A., Alkhudhiri, Bandar, Yoo, Junsoo
• Format: Article
• Language: English
• Subjects: Bubble dynamics; ENGINEERING; Infrared measurements; Liquid–vapor thermal interaction; Sliding bubbles; Subcooled flow boiling; Subcooled Flow Boiling, Sliding Bubbles, Thermal Footprint, Liquid-Vapor Thermal Interaction, Infrared Measurements, Bubble Dynamics; Thermal footprint
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/j.ijmultiphaseflow.2017.10.002

•A new life-cycle of subcooled flow boiling sliding bubble was proposed from experiments.•A “hot quenching” stage occurring at bubble detachment was included in the new life-cycle.•A characteristic thermal footprint due to “hot quenching” was found for all detaching bubbles.•Issues of conventional bubble–wall contact area measurement were identified.•A methodology was proposed to accurately measure the bubble–wall contact area. The local thermal response of the liquid phase to the presence of sliding bubbles was measured with an infrared camera in subcooled flow-boiling conditions. These measurements were complemented with two high-speed cameras to capture the corresponding bubbles’ dynamics. The liquid–vapor interactions were captured in detail over the full life-cycle of sliding bubbles. Four distinctive phases for the bubble life-cycle were identified: A) Spherical bubble growth with strong attachment, B) Deformed bubble growth with weak attachment, C) Detachment with hot liquid quenching, and D) Cold liquid quenching. To the best of the authors’ knowledge, it is the first time that the “detachment with hot liquid quenching phase has been observed. This phase is characterized by a “hot” thermal footprint during the bubble detachment process. It is believed that this footprint is constituted partially from hot liquid released during the condensation of the recently detached bubble, and from released hot fluid previously collected by the bubble during sliding. In addition, this work reveals that using traditional high-speed visualization techniques (side-view camera only) can lead to an underestimation of approximately 40% of the actual bubble–wall contact diameter (dc) which was inferred from the infrared camera measurements.