Trapping Bubbles in Liquid by Vibration Excitement: Experimental

Experiments were carried out using a setup consisting of a polyacrylate tube column, a vibration exciter, a power amplifier, a high-speed video camera and a personal computer. A schematic representation of the set-up is shown in the figure below.The polyacrylate tube has an inner diameter of 0.014 m and a height of 1.36 m. A gas injection port 0.05 m from the bottom of the tube allowed for the injection of gas bubbles into the tube by means of 0.05 mL or 1 mL syringes. The bottom of the polyacrylate tube was firmly screwed onto a shaft projecting from the top of the vibration exciter. In this way, vertical displacements of the shaft at specified amplitudes and frequencies fully corresponded to displacements of the polyacrylate tube.

The shaft was connected to an air-cooled vibration exciter (TIRAvib 5220, TIRA Maschinenbau GmbH, Germany). The vibration exciter was coupled to a power amplifier and the entire vibration setup fully controlled from a PC using SignalCalc 550 Vibration Controller software (Data Physics Corporation, United States). The frequency range of the vibration exciter is 2 Hz to 5000 Hz. Depending on the operating frequency, the amplitude can be varied between 0 mm and 12 mm. Note that the amplitude of vibration is defined as the absolute value of the maximum positive or negative displacement of the vibration exciter from its rest position. The vibration exciter was programmed to generate sine wave oscillations.

Video movies were made of trapped bubbles by the use of a Photron Fastcam-ultima 40K high-speed video camera, which has the capability of recording at between 30 frames per second (fps) and 40500 fps. The camera was connected to a memory box, which allowed for movies being made to be instantaneously stored, as well as a display monitor, which permitted real-time viewing of the movies. Lighting for the movies made was provided by a single Dedotec dedocool 250 W Halogen Photo Optic lamp. This lamp had the unique property of providing sufficient illumination without increasing the ambient temperature. After each video recording, data obtained were transferred from the memory box to a PC for analysis.

For all experiments carried out, air bubbles served as the gas phase and demineralised water as the liquid phase. All experiments were carried out at room temperature. For each experimental investigation the polyacrylate tube was filled with liquid to a height H, with the pressure at the top of the column being atmospheric.