[ gas-liquid separation ]
Fig. 3. Mechanisms of filtration separation 10
correction factor( equals 1 for d p
>> 15 microns). The larger the Stokes number, the better the separation performance. 5
The filtration efficiency by inertial impaction is given by:
Where
And β is the fibre packing density( fibre volume / total volume).¹¹ Typical range for fibrous filters is 0.01 < β < 0.1.
2. Direct interception – smaller droplets lack sufficient momentum to maintain linear motion and therefore flow around the filter media with the gas flow. They are intercepted only when the distance between the droplet and the monofilament is smaller than the droplet radius. This mechanism is characterized by the interception parameter:
K
P d � d p
b
The larger the K p
, the higher the interception efficiency. 5
3. Diffusion interception – smaller droplets < 1 micron in diameter undergo Brownian motion, increasing the probability of hitting the filter media surface and being separated. This is characterized by the Peclet number:
P e
Ud g
� D
Where D v is the diffusion coefficient of the droplets in the gas flow. Improved interception efficiency is found for smaller values of P e
. 5
The separation performance of filtration media surpasses that of vane plates due to the larger surface area for droplet interception. This can make filter separators more suitable for higher liquid contents and enable smaller vessels with reduced footprint and lower manufacturing costs. However, the presence of any solid particulate impurities can block the filter media, increase pressure drop, and lead to regular cleaning or replacement. This can increase operating costs. Currently, gas-
v b
34 Hydrogen Tech World | Issue 22 | June 2025