EXPERIMENTAL STUDY OF CHAMBER VOLUME EFFECT ON BUBBLE FORMATION FROM ORIFICE PLATES SUBMERGED IN WATER

Experimental study of air bubble formation from orifice plates submerged in water pools has been carried out. Air is forced through the orifice by supplying it to a chamber connected to the orifice plate. The chamber volume plays an important role in determining the bubble growth time as well as bubble size and shape at departure. The effect of chamber volume is generally correlated in term of a dimensionless parameter, capacitance number (N,), which is proportional to the chamber volunie and is inversely proportional to the square of the orifice diameter. To better understand and characterize this effect, an experimental study is performed using ten orifice plates of diameter ranging from 0.61 mm to 2.261 mm with six different chamber volumes between 12 cc and 59 cc with the corresponding capacitance numbers varying from 0.2 to 19. The shape and size of the bubble are captured using high speed videography. The orifice plate material is acrylic glass which has an equilibrium contact angle of 38 with pure water. It was observed that the value of critical capacitance number or AT, above which the bubble evolution is affected by the gas chamber volume, is around 0.85. The bubbles are more spherical in shape, and the growth time is significantly smaller. Also, at high capacitance number (N, > 7), the air flow in the bubble is so high that the bubble departs with a sharp apex and has a large volume. Above N,> 10, the chamber effects plateau and further increase in gas chamber volume does not alter bubble size and shape at departure.