Therefore,

The important dimensions of a gas liquid separator are diameter and height. The diameter of the vertical gas liquid separator depends on maximum allowable velocity. The limiting velocity is the terminal velocity of maximum size droplet with permissible entrainment.

...............................................(5.8)

Whereas in case of horizontal separator cross sectional area estimated is only that of the free space above the liquid. The liquid seal depth has also considers while estimating the diameter of the vessel. Height of gas phase above the liquid should be sufficient to allow the disengagement of entrained droplets. The depth of the liquid level in the vessel depends upon the retention time and is given by: