# Filter pressure drop (fluids.filters)¶

fluids.filters.round_edge_screen(alpha, Re, angle=0)[source]

Returns the loss coefficient for a round edged wire screen or bar screen, as shown in [R381385]. Angle of inclination may be specified as well.

Parameters: alpha : float Fraction of screen open to flow [-] Re : float Reynolds number of flow through screen with D = space between rods, [] angle : float, optional Angle of inclination, with 0 being straight and 90 being parallel to flow [degrees] K : float 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.

References

 [R381385] (1, 2) 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)[source]

Returns the loss coefficient for a round edged open net/screen made of one of the following patterns, according to [R382386]:

‘round bar screen’:

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

‘diamond pattern wire’:

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

‘knotted net’:

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

‘knotless net’:

$K = 0.72(1-\alpha) + 2.1(1-\alpha)^2$
Parameters: alpha : float Fraction of net/screen open to flow [-] subtype : str One of ‘round bar screen’, ‘diamond pattern wire’, ‘knotted net’ or ‘knotless net’. angle : float, optional Angle of inclination, with 0 being straight and 90 being parallel to flow [degrees] K : float Loss coefficient [-]

Notes

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

References

 [R382386] (1, 2) 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 [R383387].

Parameters: alpha : float Fraction of screen open to flow [-] K : float Loss coefficient [-]

Notes

Linear interpolation between a table of values.

References

 [R383387] (1, 2) Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: Van Nostrand Reinhold Co., 1984.

Examples

>>> square_edge_screen(0.99)
0.008000000000000009

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 [R384388].

for Dh < l < 50D

$K = \frac{0.5(1-\alpha) + (1-\alpha^2)}{\alpha^2}$

else:

$K = \frac{0.5(1-\alpha) + (1-\alpha^2) + f{l}/D}{\alpha^2}$
Parameters: alpha : float Fraction of grill open to flow [-] l : float, optional Thickness of the grill or plate [m] Dh : float, optional Hydraulic diameter of gap in grill, [m] fd : float, optional Darcy friction factor [-] K : float 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.

References

 [R384388] (1, 2) 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 [R385389].

for Dh < l < 50D

$K = lookup(alpha)$

else:

$K = lookup(alpha) + \frac{fl}{\alpha^2D}$
Parameters: alpha : float Fraction of grill open to flow [-] l : float, optional Thickness of the grill or plate [m] Dh : float, optional Hydraulic diameter of gap in grill, [m] fd : float, optional Darcy friction factor [-] K : float 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.

References

 [R385389] (1, 2) 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