Session: 07-07: Experiments and Analyses - VI

Paper Number: 136714

136714 - Flow Characteristics of Turbulent Bubbly Flow in 2x2 Rod Bundle 

Abstract: 

Although there are several experimental data of liquid velocity in single-phase turbulent flows in rod bundles, few velocity measurements have been carried out for two-phase bubbly flow in a rod bundle due to difficulties caused by the presence of gas-liquid interface. In this study, we therefore measured liquid velocity in single-phase and bubbly flows in a 2x2 rod bundle by installing a small LDV probe into the rod, by which the distance between the probe and the measurement point became short and the effects of bubbles on the measurement were reduced. The test section consisted of an acrylic duct (29 x 29 mm) and four rods installed in 2x2 matrix arrangement in the duct. The diameter and the pitch of the rods were 10 and 13 mm, respectively. The hydrodynamic diameter of the channel was 8.7 mm. The diameter of the probe was 7 mm. The probe formed the measurement volume of 29 micrometer in diameter and 140 micrometer in length. The rod consisted of the inner pipe connected to the LDV probe, the outer pipe with mirror and the FEP pipe as the rod. Since the FEP has almost the same refractive index as water, the refraction of beam at the curved wall was negligible, and therefore, accurate measurements could be achieved. The experiments were carried out for the liquid volume fluxes of 0.5 and 1 m/s, and for single-phase flow and bubbly flow with the gas volume flux of 0.08 m/s. The results showed that the distribution of axial mean liquid velocity was flattened due to the presence of bubbles in the low liquid volume flux case, whereas it was not clear in the high liquid volume flux case. Turbulence intensity was augmented due to the presence of bubbles in the low liquid volume flux case, whereas it was not significant in the high liquid volume flux case, in which the magnitude of the liquid velocity fluctuation was comparable to the relative velocity between the bubbles and liquid. Local wall shear stress on the rod wall can be evaluated by using the small LDV probe. The Reynolds shear stress in the vicinity of the rod wall was enhanced by bubbles due to the increase in the velocity gradient in the near wall region. The Prandtl’s mixing length hypothesis held in the vicinity of the rod even in the bubbly flow and the mixing length in the center region of the subchannel was close to the bubble radius.

Presenting Author: Shigeo Hosokawa Kansai University

Presenting Author Biography: Shigeo Hosokawa is a Professor of Societal Safety Sciences at Kansai University, Japan. He graduated from Kobe University in 1988, and received degree of Dr. Eng. from Kobe University in 1993. He has been working in Kobe University as a research associate from 1993 to 1998 and as an associate professor from 1998 to 2019. He moved to Kansai University as the current position in 2019. His areas of expertise include experimental diagnostics of thermo-fluid flow, turbulence, interfacial phenomena, application and generation of fine-bubbles, safety issues in thermo-fluid systems as well as development of optical measurement techniques for heat and fluid flows.

Authors:

Shigeo Hosokawa Kansai University
Akio Tomiyama Kobe University