Abstract: In order to obtain the bubble size distribution in the mold， a water model system was developed with air blowing through a circumferential inlet chamber made of specially-coated mullite porous brick， which is used as the actual upper nozzle. The transient bubble distributions in the mold were captured by a high-speed video camera under a laser light beam. Then， the location and size of bubbles were measured using the image analysis software of ImageJ. The results show that the average bubble size increases with increasing the water flow rate and SEN immersion depth， decreases with increasing the gas blowing rate and nozzle port angle. The initial bubble size obtained from the mullite brick is small and uniform. The bubble size along the horizontal direction of wide wall increases first and then decreases. With the increase of water flow rate， the bubble distribution is more dispersed. With the increase of gas blowing rate， there is no obvious difference for the bubble distribution; however， the bubble size was increased.

Key words: continuous casting mold, coalescence, breakage, bubble size distribution, water model experiment