ULTRASONIC MEASUREMENTS OF BUBBLE SHAPE AND LIQUID FILM THICKNESS OF A TAYLOR BUBBLE RISING IN A STAGNANT WATER COLUMN

Resumo

The present paper reports a preliminary study of direct measurement of the equilibrium thickness of the falling film around a Taylor bubble in a stagnant water column, using the pulse-echo ultrasonic technique. The experiments were conducted in an acrylic tube of 1.8 m long with inner diameter of 25.21 mm and wall thickness of 6.8 mm. A Taylor bubble was formed by the invertion of the pipe, sealed at the ends and partially filled with water to leave an air pocket of length L0. The rising Taylor bubble was detected by a transducer located 400 mm from the top of the pipe. Ten measurements were made for each of the four channels of the ultrasonic system, using the same settings of the system parameters, totaling 40 measured bubbles. A simplied Brown's model for the thickness around a Taylor bubble was used to calculate a reference value of the parameter being measured. We found that the values directly measured by the ultrasonic technique were in good agreement with the reference value calculated and thus conclude that the pulse-echo ultrasonic technique can be applied to directly measure the thickness of the 
film around the Taylor bubbles in acrylic tubes. The errors between the experimental and the reference values were in the order of 10%.