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.
Highlights
C D f Fr g HAS ID LAS PSD St XVariable [–] Pipe diameter [m] Frequency [Hz] Froude number [–] Gravitationnal acceleration [m sÀ2] Highly Aerated Slug Internal diameter Less Aerated Slug Power Spectral Density Strouhal number [–] Lockhart-Martinelli parameter [–] Greeks letters kInput fraction [–] q Density [Kg mÀ3] Subscripts G Gas L Liquid s
The present experimental investigation, based on flow visualization and pressure drop signals, carried on the onset of intermittent flow in a 30 mm ID pipe led to the following conclusions:
– The liquid superficial velocity VSL plays a great role on the formation of intermittent flow
Summary
Variable [–] Pipe diameter [m] Frequency [Hz] Froude number [–] Gravitationnal acceleration [m sÀ2] Highly Aerated Slug Internal diameter Less Aerated Slug Power Spectral Density Strouhal number [–] Lockhart-Martinelli parameter [–]. The onset of a slug is due to the initiation of a disturbance, at the gas-liquid interface of the stratified flow, at the inlet of the pipe. From a theoretical point of view, the onset of intermittent flow gave rise to numerous works [8, 18,19,20,21] and the Taitel and Dukler model [19] remains a relevant reference This model is not easy to implement since it uses graphical/iterative solution to determine the equilibrium liquid level in a pipeline, for a given set of flow conditions. Salhi [26] observed visually in a 40 mm ID pipe that the onset of slug flow occurs for high gas superficial velocities due to the increase of the gas-liquid wavy interface. The present study was undertaken to provide statistical information on a parameter of a primary interest in the petroleum industry i.e. the slug frequency
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