GAS DISPERSION PHENOMENA AT A NARROW SLOT SUBMERGED IN A LIQUID

When air or helium was injected upwards into water or methanol through long, narrow slots of width 50 less than or equal to w less than or e qual to 250 mu m formed in a horizontal surface, small bubbles were ge nerated spontaneously and continuously at an array of discrete sources distributed distance lambda apart along the slot. The dimensionless s ource spacing was found by experiment to be lambda/w = 17.2(rho(l)/rho (g))(0.16)We(-0.25), where (rho(l)/rho(g)) is the liquid-gas density r atio and We is the modified Weber number for the slot flow. (We = U(s) (2)w rho(l)/sigma, where U-s is the superficial gas velocity in the sl ot and sigma is the liquid interfacial tension.) The existence and spa cing of the sources is attributed to the formation of curvature-depend ent Rayleigh-Taylor nodes at the ''most dangerous'' wavelength on the gas-liquid interface in the slot. A new analysis of the node wavelengt h is presented for this interface configuration. Bubble volume V-b was found to increase with U-s up to a critical value of U-s given for wa ter by the dimensional equation U-s = 115 rho(g)(-0.12)W(-0.068), beyo nd which lateral coalescence occurred between neighbouring growth site s with a consequent breakdown of the discrete source array.