The flow regime and droplet diameter is important steps in sizing the gas/liquid separators. The selection of flow regime depends on the location of the separators. For example, if the separator is at suction of a compressor, the flow regime should be stratified flow to facilitate liquid separation from gas in separators

1. FLOW REGIME AND DROPLETS DIAMETER CALCULATIONS
The feed entering the gas-liquid separator can be in the form of mist, stratified flow, slug flow
depending on the flow rates and physical properties of the gas and liquid phases and on the feed
pipe characteristics
The basic categories of droplets:
 Sprays are droplets greater than 10 microns in diameter.
 Mists are droplets less than or equal to 10 microns in diameter.
 Aerosols are less than or equal to 1 microns in diameter.
1. Determine the gas and liquid Froude number
Fronde number is dimensionless quantity defined as the ratio of flow inertia to the
external field (usually gravity).
Gas Fronde number:
𝐹𝑟 𝑔
= 𝑉𝐺√
𝜌 𝐺
𝐷𝑓𝑝 𝑔 (𝜌𝑙 − 𝜌 𝐺)
𝐹𝑟 𝐿
= 𝑉𝐿√
𝜌 𝐿
𝐷𝑓𝑝 𝑔 (𝜌𝑙 − 𝜌 𝐺)
Frg, FrL : gas and liquid Froude number respectively
𝜌G, 𝜌 L: gas and liquid density
VG, VL: Superficial gas and liquid velocity respectively
Dfp: Inlet pipe diameter

2. FLOW REGIME AND DROPLETS DIAMETER CALCULATIONS
g: acceleration due to gravity
Using the liquid Froude number (y-axis) and the gas Froude number (x-axis) to define the
flow regime based on the configuration of the pipe
Two phase flow map for horizontal feed pipes
Two phase flow map for Vertical feed pipes

3. FLOW REGIME AND DROPLETS DIAMETER CALCULATIONS
2. Determine the diameter of the largest droplets, dp,max formed in the feed pipe:
𝐷 𝑃max
𝐷𝑓𝑝
= 4.5 (
𝜎
𝜌 𝑔 𝑉𝐺
2
𝑑 𝑓𝑝
)
0.6
(
𝜌 𝐺
𝜌𝑙
)
0.4
Dp,max : Maximum droplet diameter
Dfp : Inelt pipe diameter
σ: gas/liquid interfacial tension