(annular_flow)=
# Annular flow

```{admonition} Reference
- {cite:t}`Wallis1969-kj`
```

Annular flow is one of the typical flow patterns observed in two-phase flows. This flow pattern consists of a fast gas core and a liquid film formed on the channel wall. In a circular pipe, the liquid film exhibits a ring-like shape; hence, it is referred to as *annular*. Annular flows are formed at high gas flow rates, and the void fraction is therefore typically high, and the liquid film is thin. We consider here co-current upward and counter-current annular flows, which have their practical importance in nuclear and chemical engineering applications. 

```{toctree}
:maxdepth: 1

annular_flow/af_upward_cocurrent
annular_flow/af_countercurrent
annular_flow/af_ccfl
```