An upflow granular-media filter routes liquid from a lower distributor through a media bed to an upper outlet. This calculator is a superficial-velocity and entered-expansion comparison, not a filtration-performance or fluidization model.
Upward Flow Filter Interactive Calculator
Enter flow, bed area, static depth, an assumed expansion percentage and available freeboard. Results are direct geometry only; the tool does not predict expansion from flow or establish an acceptable operating range.
Equation Used
- Flow is divided uniformly by entered plan area for superficial velocity.
- Static bed depth and expansion percentage are user-entered.
- Available freeboard is measured above the static bed surface in the same vertical datum.
- The margin is purely geometric and does not include trough clearance, surge, splashing or a safety allowance.
- Media size, density, porosity, grading, water properties, temperature, head loss, fluidization, solids capture, backwash effectiveness, effluent quality and equipment ratings are omitted.
Upflow Through a Granular Bed
EPA material describes filters designed for either upflow or downflow and identifies the underdrain as the structure supporting the bed and distributing or collecting flow. During backwash, upward velocity can fluidize and expand media; that does not make every service-flow operating point a fluidized bed.
The animation shows a generic vessel, lower distributor, granular bed and upper outlet.
What This Calculator Represents
The tool divides entered volumetric flow by entered bed plan area, then applies an entered expansion percentage to entered static depth. Available freeboard is compared only with that entered expansion rise.
Direct Flow and Expansion Geometry
entered expansion rise = H × E/100
expanded bed depth = H + expansion rise
geometric freeboard margin = F − expansion rise
Worked Arithmetic Example
At 10 m³/h through 1.0 m², superficial velocity is 10 m/h. A 1.0 m static bed with entered 10% expansion rises 0.10 m to 1.10 m. With 0.30 m available freeboard, the geometric margin above that rise is 0.20 m.
Model Boundary
- Calculated: flow/area and entered-percent height arithmetic.
- Illustrated: generic upflow vessel and bed.
- Not calculated: actual bed expansion, minimum fluidization velocity, service or backwash limits, media loss, head loss, solids capture, run length, effluent quality, distributor uniformity, trough clearance, pressure rating or safety.
Frequently Asked Questions
Does the tool predict bed expansion from flow?
No; expansion percentage is entered.
Is the superficial velocity an approved operating rate?
No.
Is expansion rise a minimum freeboard requirement?
No.
What does a negative geometric margin mean?
The entered rise exceeds entered freeboard; no hydraulic consequence is predicted.
Are head loss and turbidity calculated?
No.
Can this calculator size a filter?
No.
References
- U.S. EPA, Surface Water Treatment Rule Turbidity Guidance Manual: backwash rate as flow divided by filter area and measurement of bed expansion; manufacturer consultation for proper expansion.
- U.S. EPA, Nutrient Control Design Manual: upward backwash, fluidization and expanded-bed depth dependencies.
- U.S. EPA, Tertiary Granular Filtration: Problems and Remedies: upflow/downflow configurations, underdrains and backwash expansion.
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