الفهرس 
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Abstract
A double electric resistivity. probe was designed to investigate bubbly flow characteristics including local’ void fraction” bubble frequency, bubble chord length and bubble velocity and their distributions in the radial direction in a vertical-bubble column and an upward gas-liquid ’(air-water) in an annular vertical channel. An electric circuit was designed to convert the analog signals measured by the two-resistivity probe into square signals- A data acquisition systef!1 was used to collect the output of the probe electric circuit at a. sampling rate of 1000 samples’ per second per channel. A subroutine was developed to analyze the data collected by the data, acquisition system to obtain void fraction, bubble, frequency, bubble velocity and ,bubble diameter distributions, Measurements of bubble characteristics in still water indicated core void fraction and bubble’ frequency, flat bubble rise velocity and chord length profiles. Results of void fraction are in reasoi1able agreement with the ,void fraction determined from pressure drop measurement along the test section and the results of the bubble velocity are in good agreement with data of [19, 7, 23]. Measurements of bubble characteristics in flowing water were made in a bubbly flow regime, where (a. < 0.3) at air superficial velocity ranging from 0.038 to 0.0612 in/s and water superficial velocity ranging from 0.0123 to 0.0343 in/s and perforation ratio ranging from 1.486 *. 10’3 to 0.01435. Results indicated core void fraction and bubble frequency and flat bubble velocity and chord length profiles. Results of the bubble velocity and bubble chord length are in good agreement with data of [7,23]. Void fraction, bubble frequency, bubble velocity’ and . bubble chord length radial distributions were obtained for various water and airflow rates and perforation ratios. The void fraction profiles indicated maximum values near the inner wall. Bubble frequency distributions gave similar results as the void fraction. Bubble velocity distributions had low values near inner and outer walls and indicated high values near the center of the annular gap. The perforation ratio of the bubble generation disk showed large effect on the bubble size.