Upward air–water bubbly flow characteristics in a vertical square duct

Abstract

In nuclear engineering fields, gas-liquid bubbly flows exist in channels with various shape and size crosssections. Although many experiments have been carried out especially in circular pipes, those in a noncircular duct are very limited. To contribute to the development of gas-liquid bubbly flow model for a noncircular duct, detail measurements for the air-water bubbly flow in a square duct (side length: 0.136 m) were carried out by an X-type hot-film anemometry and a multi-sensor optical probe. Local flow parameters of the void fraction, bubble diameter, bubble frequency, axial liquid velocity and turbulent kinetic energy were measured in 11 two-phase flow conditions. These flow conditions covered bubbly flow with the area-averaged void fraction ranging from 0.069 to 0.172. A pronounced corner peak of the void fraction was observed in a quarter square area of a measuring cross-section. Due to a high bubble concentration in the corner, the maximum values of both axial liquid velocity and turbulent kinetic energy intensity were located in the corner region. It was pointed out that an effect of the corner on accumulating bubble in the corner region changed the distributions of axial liquid velocity and turbulent kinetic energy intensity significantly.

Liquid Velocity Profile of Turbulent Bubbly Flow in a Large Square Duct

“…The αg distribution at z=10.1DH is used since the flow at z=16DH was developed based on αg distribution before entering this part such as z=10.1DH. Besides, it has already reached the developed status at z=4.5DH [15], so the choice of αg distribution at different locations have no effect on the following analysis.…”

“…With the measured experimental mean pressure gradient dP/dz and αg distributions [1] and assuming dP/dz to be uniform among cross sections, Figs. 4(a), 4(c), 5(a) and 5(c) show the lateral distributions of F along the bisector and the diagonal lines, respectively.…”

“…So far, the models proposed are always based on the database obtained in the small pipes not only circular but also the noncircular ducts. Therefore, to improve the understanding and modeling of TBF in the large diameter and noncircular duct, more experimental databases and numerical validation of the existed models or some new models are necessary based on our understandings from the latest experimental observations [1]. Recent studies [1,14,15] established the detailed database of upward TBF in a large vertical square duct.…”

“…Therefore, to improve the understanding and modeling of TBF in the large diameter and noncircular duct, more experimental databases and numerical validation of the existed models or some new models are necessary based on our understandings from the latest experimental observations [1]. Recent studies [1,14,15] established the detailed database of upward TBF in a large vertical square duct. Similar to that in other noncircular ducts [11], the pronounced corner and wall peaks of void fraction were observed for the low averaged void fraction cases.…”

“…55R61, Cylindrical sensor outer diameter is 70 μm and the length is 1.25 mm) and a multi-sensors optical probe. Totally 66 or 121 measuring points were adopted in an octant triangular area (surrounded by bisector and diagonal lines) as shown [1]. Besides, six pressure taps were set at the axial positions of z/DH = 1, 5, 10, 15, 16.5 and 19, respectively in order to measure the pressure drop by the differential pressure transmitters (±0.1% F.S.…”