This kind of internal is commonly implemented to separate a liquid-liquid mix using the different densities of the two liquids. They are often used in many three-phase separators where the flow is composed of gaseous phase, heavy liquid phase (ex. water) and light liquid phase (ex.: oil).

 The plate pack coalescer is composed of canals between long parallel plates at a fixed angle. Passing through these canals with an adequate speed, the separation of the light phase and the heavy phase can be achieved. At the exit of the pack the light liquid is placed above the heavy phase and can be separated with a weir (see the scheme).