Paper Title
Enhancement Techniques of Bubble Lift-Off from A Heated Surface in Subcooled Flow Boiling

Subcooled flow boiling is widely used for cooling of high-power densitydevices due to its high heat transfer coefficient. In the subcooled boiling region in a heated channel, bubble nucleation occurs near the heated wall although the bulk liquid temperature is still below the saturation temperature. If many bubbles stay in the wall region of high temperature, they coalesce to merge into distinctly large bubbles. This would cause serious technical problems in industrial systems,such as the noise appearing in the X-ray computed tomography images, the two-phase flow instability encountered in evaporation tubes, and rapid rise of wall temperature due to the departure from nucleate boiling. In the present work, several sophisticated ways to retard the large bubble formation were proposed to maintain efficient cooling in subcooled flow boiling. In the subcooled boiling region, cold liquid is present in the bulk region away from the wall. The bubbles would hence condense to disappear if they are lifted off the heated wall. Thus, to enhance the bubble lift-off from the wall, the two methods were proposed. One was improving the wettability and/or wickability of the heated surface to convey the cold liquid to the wall region, and the other was adding swirling motion to the main flow. Combined use of these methods was also considered promising.The importance of experimental validation was emphasized to confirm the effectiveness of these methodsin maintaining sufficiently low void fraction in the subcooled boiling region. Keywords - Subcooled Flow Boiling, Void Fraction, Large Bubble, Lift-off, Condensation.