Two-phase interfacial structure of bubbly-to-slug transition flows in a 12.7 mm ID vertical tube

TL;DR

This study experimentally investigates the interfacial structure during bubbly-to-slug flow transition in a small vertical tube, providing new data and a correlation for distribution parameters relevant to flow modeling.

Contribution

It offers an experimental database for bubbly-to-slug transition flows in small tubes and proposes a new correlation for the distribution parameter in the Drift Flux model.

Findings

Wall-peak void distribution does not appear in small diameter tubes during transition.

Distribution is related to void fraction and bubble size relative to tube size.

A new correlation for the distribution parameter in the Drift Flux model is proposed.

Abstract

This experimental study focuses on the characteristics of air-water two-phase interfacial structure. Interfacial parameters including void fraction, interfacial area concentration, and bubble interfacial velocity are measured using four-sensor electrical conductivity probe on a 12.7 mm ID vertical tube. The tube size is approximately equal to the maximum distorted bubble size. Therefore, the bubbly-to-slug transition characteristics can be different from in other sizes of tubes. Comparing with previous studies, this study provides an experimental database with a wide range on the bubbly-to-slug transition flows, with 4 different superficial liquid velocities (0.3, 0.5, 1.0, and 2.0 m/s) and void fraction ranging from 0.07 to 0.66. Experimental results show that the wall-peak void distribution does not appear in a small diameter tube under the bubbly-to-slug flow transition flow. The distribution is related with both void fraction and the relative bubble size to the tube size. In this sense, a new correlation of distribution parameter in the Drift Flux model is proposed based on the previous studies by Ishii and Hibiki et al. This experimental study can be a good reference for the model development of flow regime transition and the Interfacial Area Transport Equation.