a suspension of the solid abrasive in the liquid a homogeneous suspension of abrasive and liquid although desired is however not necessary for the wet foam blasting mechanism to work effectively the gas sparger orifice size in combination with the gas flow rate vessel size and the viscosity density and interfacial surface tension of both the liquid phase and the resulting foam affect the stability and size of the bubbles in the foam the initial size of the bubble produced in the liquid phase at the tip of the sparger is largely determined by the orifice s diameter liquid density and the interfacial tension of the gas and liquid film for singularly produced bubbles from a sparger empirical equations suggest that bubble sizes vary proportionally to the cube root of the orifice diameter accordingly the foaming characteristics of the orifice are fairly insensitive to the orifice size unless a fritted filter type of gas disperser is substituted for an open orifice in the preferred embodiment discussed later a foam with bubbles approximately 1 4 inch in diameter is desired a foam consisting of bubbles significantly less than 0 1 inches in diameter produces flow friction in the exit tubing 8 and nozzle 10 which diminishes the effectiveness and velocity of the exit stream this in turn restricts the ultimate blasting force of the sandblaster apparatus a foam is formed when gas bubbles pass through and rise to the surface of the liquid slurry and persist without coalescence with one another or without rupturing into the vapor space above the liquid the duration and sustenance of the foam is determined by and.