Heat Transfer Enhancement Due to Marangoni Flow Around Moving Bubbles During Nucleate Boiling

Introduction Nucleate boiling has always been an important heat transfer mechanism in many fields, such as energy utilization, manufacturing processes, and chemical processing and nucleate boiling continues to find new applications in many new areas, such…

Heat Transfer Enhancement Due to Marangoni Flow Around Moving Bubbles During Nucleate Boiling

Nucleate boiling is a very efficient method for generating high heat transfer rates from solid sur- faces; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. The heat transfer mechanisms around stationary and moving bubbles on very thin microwires were analyzed numerically to evaluate the effect of the bubble motion on the heat transfer from the wire sur- face. The numerical analysis accurately models the experimentally observed bubble movement and fluid ve- locities. The analytical model includes the effects of the Marangoni flow around the bubble and the evapora- tion and condensation within the bubble. The analysis shows that the heat transfer was significantly en- hanced by the Marangoni flow around the outside of the bubble which transfers at least twice as much en- ergy from the wire as the heat transfer directly from the wire to the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles. The moving bubbles also created a wake that further enhanced the heat transfer from the wire. Since the Marangoni number for water is greater than for ethanol for the same conditions, the Marangoni flow and, hence, the bubble velocities are predicted to be greater in water than in ethanol.