Onset of intermittent flow: Visualization of flow structures

Abstract

The transition from stratified to intermittent air-water two-phase flow was investigated experimentally, by flow visualization and pressure drop signals analyses, in a 30 mm ID pipe. The intermittent flow’s onset was found to be mainly dependent on the liquid superficial velocity and the pipe diameter. Plug flow, Less Aerated Slug (LAS) or Highly Aerated Slug (HAS) flows could be obtained on the gas superficial velocity grounds. The available models, compared to experiments, could not predict adequately the intermittent flow onset. The appearance of liquid slugs was revealed by peaks in the pressure drop signal. Furthermore, it was shown that the available slug frequency correlations were not valid in the zone of the onset of intermittent flow.

Identifying the intermittent flow sub-regimes using pressure drop time series fluctuations

“…The originality of this work resides also in the use of feature space using the parameters obtained from calculated statistical moments and PDF. This paper is a continuation of our works on plug, LAS and HAS ow sub-regimes observed in a 30 mm ID pipe (Arabi, 2019;Arabi et al, 2020bArabi et al, , 2021bArabi et al, , 2021c).…”

“…For the detail of the uncertainty associated with the instrumentation used, the readers can be oriented to the refs. (Arabi, 2019;Arabi et al, 2020Arabi et al, , 2021b. For each ow pair of super cial velocities, a signal of 30 s duration was sampled with a frequency of 500 Hz.…”

Analysis of Horizontal Gas-liquid Intermittent Flow Sub-Regimes Transitions: Physical Mechanisms and Flow Maps

“…The resulting Plug/LAS and LAS/HAS ows transition lines were also represented. The strati ed/intermittent ow line reported in our previous study (Arabi et al, 2021b) using the same experimental setup, has been also depicted. As discussed in section 3.1, it can be seen from Fig.…”

“…7. We have also represented the points corresponding to the onset of intermittent ow obtained using the same experimental device published in Arabi et al (2021b). It is clear that the majority of the points falls within the intermittent ow area of the map, including plug and slug ow.…”

“…It was reported that the bubbly-to-intermittent ow occurs at a higher liquid super cial velocity in larger pipe diameter. Various studies (Kong et al, 2018a;Thaker and Banerjee, 2015;Dinaryanto et al, 2017;Deendralianto et al, 2019;Arabi et al, 2021b) showed that an increase in diameter leads to an increase in liquid super cial velocity for the strati ed-to-intermittent transition. Pereyra et al (2012) proposed a methodology to quantify the con dence level in the prediction of gasliquid two-phase ow regimes given by the ow maps or the transition models.…”