Visual study on bubble motion characteristic in rectangular channel under transient external force field

Bubble motion characteristic in a rectangular channel under the sway and heave rolling is observed using high speed digital camera. It is found that the influence on the single bubble growth for the isolated bubble region is little, but the bubble departure diameter decreases with increasing motion frequency. During the increasing of number of bubbles, the obvious influences of transient motion conditions on the bubble motion are observed. The number and size distributions of bubbles becomes asymmetric and the bubble moving sometimes fast and sometimes slow in a motion period. As a result, the heating wall temperature exhibits a periodic fluctuation of small amplitude, and so the two-phase boiling heat transfer coefficient is also changed. The above phenomena are more apparent as the motion amplitude and frequency increasing. (authors)