Experimental Investigation of Sinking a Buoyant Body in Water With Bubbles

摘要

The introduction of gas bubbles into a liquid decreases the average density, and thus decreases the buoyant force on a floating body. This thesis investigates the critical average density required to sink a buoyant body in water with rising bubbles. A volume of bubbly water is created in a clear acrylic tube of inner diameter 30 cm and height 60 cm, that is closed at the bottom and open at the top. An array of diffusers at the bottom produces 2 mm diameter bubbles distributed uniformly over the cross section of the tube. A 10- cm diameter hollow steel ball whose average density is varied from 0.70 to 0.99 g/cm3 is employed as the buoyant body. A theory of the critical density for sinking is developed, and predicts that the average fluid density is greater than the ball density for sinking. The experimental data, which include a quantitative error analysis, agree well with the theory for average ball densities from 0.94 to 0.99 g/cm3, but show a definite trend of fluid densities that are 3smaller than those predicted for 0.70 to 0.94 g/cm3.