Filter pressure drop (fluids.filters)

This module contains correlations for the loss coefficient of various types of filters in a pipe or channel.

For reporting bugs, adding feature requests, or submitting pull requests, please use the GitHub issue tracker or contact the author at Caleb.Andrew.Bell@gmail.com.

Loss Coefficients for Screens

fluids.filters.round_edge_screen(alpha, Re, angle=0.0)[source]

Returns the loss coefficient for a round edged wire screen or bar screen, as shown in [1]. Angle of inclination may be specified as well.

Parameters
alphafloat

Fraction of screen open to flow [-]

Refloat

Reynolds number of flow through screen with D = space between rods, []

anglefloat, optional

Angle of inclination, with 0 being straight and 90 being parallel to flow [degrees]

Returns
Kfloat

Loss coefficient [-]

Notes

Linear interpolation between a table of values. Re table extends from 20 to 400, with constant values outside of the table. This behavior should be adequate. alpha should be between 0.05 and 0.8. If angle is over 85 degrees, the value at 85 degrees is used.

The velocity the loss coefficient relates to is the approach velocity before the screen.

References

1

Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: Van Nostrand Reinhold Co., 1984.

Examples

>>> round_edge_screen(0.5, 100)
2.0999999999999996
>>> round_edge_screen(0.5, 100, 45)
1.05
fluids.filters.round_edge_open_mesh(alpha, subtype='diamond pattern wire', angle=0.0)[source]

Returns the loss coefficient for a round edged open net/screen made of one of the following patterns, according to [1]:

‘round bar screen’:

K=0.95(1α)+0.2(1α)2K = 0.95(1-\alpha) + 0.2(1-\alpha)^2

‘diamond pattern wire’:

K=0.67(1α)+1.3(1α)2K = 0.67(1-\alpha) + 1.3(1-\alpha)^2

‘knotted net’:

K=0.70(1α)+4.9(1α)2K = 0.70(1-\alpha) + 4.9(1-\alpha)^2

‘knotless net’:

K=0.72(1α)+2.1(1α)2K = 0.72(1-\alpha) + 2.1(1-\alpha)^2
Parameters
alphafloat

Fraction of net/screen open to flow [-]

subtypestr

One of ‘round bar screen’, ‘diamond pattern wire’, ‘knotted net’ or ‘knotless net’.

anglefloat, optional

Angle of inclination, with 0 being straight and 90 being parallel to flow [degrees]

Returns
Kfloat

Loss coefficient [-]

Notes

alpha should be between 0.85 and 1 for these correlations. Flow should be turbulent, with Re > 500.

The velocity the loss coefficient relates to is the approach velocity before the mesh.

References

1

Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: Van Nostrand Reinhold Co., 1984.

Examples

>>> round_edge_open_mesh(0.96, angle=33.)
0.02031327712601458
fluids.filters.square_edge_screen(alpha)[source]

Returns the loss coefficient for a square wire screen or square bar screen or perforated plate with squared edges, as shown in [1].

Parameters
alphafloat

Fraction of screen open to flow [-]

Returns
Kfloat

Loss coefficient [-]

Notes

Linear interpolation between a table of values. The velocity the loss coefficient relates to is the approach velocity before the screen.

References

1

Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: Van Nostrand Reinhold Co., 1984.

Examples

>>> square_edge_screen(0.99)
0.008000000000000007

Loss Coefficients for Grills

fluids.filters.square_edge_grill(alpha, l=None, Dh=None, fd=None)[source]

Returns the loss coefficient for a square grill or square bar screen or perforated plate with squared edges of thickness l, as shown in [1].

for Dh < l < 50D

K=0.5(1α)+(1α2)α2K = \frac{0.5(1-\alpha) + (1-\alpha^2)}{\alpha^2}

else:

K=0.5(1α)+(1α2)+fl/Dα2K = \frac{0.5(1-\alpha) + (1-\alpha^2) + f{l}/D}{\alpha^2}
Parameters
alphafloat

Fraction of grill open to flow [-]

lfloat, optional

Thickness of the grill or plate [m]

Dhfloat, optional

Hydraulic diameter of gap in grill, [m]

fdfloat, optional

Darcy friction factor [-]

Returns
Kfloat

Loss coefficient [-]

Notes

If l, Dh, or fd is not provided, the first expression is used instead. The alteration of the expression to include friction factor is there if the grill is long enough to have considerable friction along the surface of the grill.

The velocity the loss coefficient relates to is the approach velocity before the grill.

References

1

Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: Van Nostrand Reinhold Co., 1984.

Examples

>>> square_edge_grill(.45)
5.296296296296296
>>> square_edge_grill(.45, l=.15, Dh=.002, fd=.0185)
12.148148148148147
fluids.filters.round_edge_grill(alpha, l=None, Dh=None, fd=None)[source]

Returns the loss coefficient for a rounded square grill or square bar screen or perforated plate with rounded edges of thickness l, as shown in [1].

for Dh < l < 50D

K=lookup(alpha)K = lookup(alpha)

else:

K=lookup(alpha)+flα2DK = lookup(alpha) + \frac{fl}{\alpha^2D}
Parameters
alphafloat

Fraction of grill open to flow [-]

lfloat, optional

Thickness of the grill or plate [m]

Dhfloat, optional

Hydraulic diameter of gap in grill, [m]

fdfloat, optional

Darcy friction factor [-]

Returns
Kfloat

Loss coefficient [-]

Notes

If l, Dh, or fd is not provided, the first expression is used instead. The alteration of the expression to include friction factor is there if the grill is long enough to have considerable friction along the surface of the grill. alpha must be between 0.3 and 0.7.

The velocity the loss coefficient relates to is the approach velocity before the grill.

References

1

Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: Van Nostrand Reinhold Co., 1984.

Examples

>>> round_edge_grill(.4)
1.0
>>> round_edge_grill(.4, l=.15, Dh=.002, fd=.0185)
2.3874999999999997