Rate of flow and mechanics of bubble formation from single submerged orifices. I. Rate of flow studies

A study has been made of the rate of flow and mechanics of bubble formation from single submerged orifices 1/64, 1/32, 1/16, and 1/8 in. in diameter installed in an 8-in. I.D. column operating in the air-water system. The coefficients of discharge obtained for sharpedged orifices operating with this system indicate that the effective orifice discharge area for this type of operation is greater than that for an orifice of the same size and type operating at the same pressure ratio in the air-air system. The effective orifice discharge areas for a round-edged orifice operating in either the air-water or air-air systems appear to be identical at the same pressure ratio. The thick-plate orifice operating in the air-water system exhibits a constancy of discharge coefficient at ratios of the downstream to upstream pressures less than 0.33. Inasmuch as bubble formation occurring close to the downstream face of a sharp-edged orifice operating in the air-water system influences the effective orifice discharge area, liquid physical properties may be expected to be important in determining the rate of flow from this type of orifice for other gas-liquid systems. In Part II photographic studies of bubble formation reveal that nonuniformity of bubble size is initiated by the onset of turbulence in the air stream flowing through the orifice. In the section of the laminar-flow range studied in this investigation (200 < NRe < 2,100) the frequency of bubble formation is nearly constant with respect to Reynolds number. The bubble size is relatively uniform at a given Reynolds number and depends markedly upon orifice diameter. Stroboscopic examination reveals that as turbulence is fully developed for the air flow through the orifice, a counterclockwise spiraling, swirling motion of the air jet is initiated. In the turbulent-flow range the bubblesize–distribution data are fitted reasonably well by a logarithmic-normal-probability distribution. More data for bubble formation in other liquids (particularly liquids of low surface tension) are necessary before a general correlation for bubble size in gasliquid systems can be developed.