Bubbling is commonly used in pyrometallurgical vessels to enhance mass and heat transfer. These processes can be difficult to monitor because of the severe operating conditions associated with these processes. Cold modeling experiments have been performed to analyze all the signals of the bubble flow inside a cylindrical vessel. The inner diameter and height of the vessel are 420 mm and 500 mm respectively, representing a 1/10th scale steel ladle. The height of water was kept 210 mm to simulate liquid steel; and the depth of motor oil (SAE 20, density ρ=0.85x10- 3kg/m3) which simulated slag, varied from 5 mm to 20 mm in 5 mm increments. The color of the oil was light brown and could be easily discriminated from the water by the naked eye. Compressed air was injected into the bath through a 3-mm nozzle flush at the bottom of the vessel at flow rate varied from 2.0 to 20.0 lpm at 2.0 lpm intervals. The air pressure was fixed to 200.0kPa at the exit of a compressed gas tank and the air flow rate was controlled by a standard rotameter with an accuracy of 3%. A digital video camera was used to record images (960x720 pixels) at 15 frames per second, and an accelerometer was installed on the outside wall of the vessel to collect the vibration signals.