Calculation of filter pressure drop
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ΔP – Pressure loss, in Paλ – Friction coefficient, dimensionless
Re – Reynolds number; Re = (ω·dn)/u, dimensionless
ω – Fluid velocity, in m/s
ρ – Fluid density, in kg/m3
μ – Dynamic viscosity, in kg/m·s
u – Kinematic viscosity; u = μ/ρ, in m/s
L – Equivalent straight pipe length, in m; refer to the table “Relationship between nominal diameter and equivalent straight pipe length for cartridge filters” for details.
D – Inner diameter of the cartridge filter, in m
dn – Equivalent diameter, in m; for cartridge filters, this value is taken as the inner diameter “D”; for shell-and-tube filters, it is taken as ‘4s/c’.
S – Liquid flow area, in m2
C – Wet perimeter of the liquid flow path; C = 2 × (inner diameter of the cylinder + height of the cylinder), in m
ξt – Inlet resistance coefficient, taken as 1.1
ξc – Outlet resistance coefficient, taken as 0.5
Relationship between nominal diameter and equivalent straight pipe length:
Nominal diameter: DN50, 80, 100, 150, 200
Equivalent straight pipe length L (×10 mm): 25∽30, 18∽23, 15∽20, 22∽38, 32∽40
Nominal diameter: DN250, 300, 350, 400, 450
Equivalent straight pipe length L (×10 mm): 27∽43, 58∽65, 48∽85, 60∽95, 62∽98
I have a gentle question: the resistance of a filter is related to the mesh size, right?
The increase in filter resistance is caused by factors such as impurities clogging the filter or changes in process conditions
This calculation process is mainly based on the Fanning formula, and it is similar to normal hydraulic calculations. In practical applications, Y-type filters or temporary V-type filters are commonly used. In such cases, the calculation focuses on the relationship between the resistance coefficient and the mesh size of the filter screen. For example, in V-type filters, the flow capacity is measured by the ratio of the open area to the total area; the calculation emphasizes the resistance generated when the proportion of open areas is 50%, 60%, 70%, etc., and the filter becomes clogged. Filters are usually installed at the pump inlet; if a simple calculation is done without taking into account clogging conditions and an appropriate margin is not chosen, the pump will be unable to draw in air, resulting in cavitation.
The actual circumstances definitely need to be taken into account