How to use this calculator
A practical workflow for geometry checks and preliminary process sizing.
1. Choose an element
Select a standard element preset or choose custom. Presets populate diameter, area, spacer, and vessel values.
2. Enter sheet geometry
Provide sheet length, sheet width, leaf count, active sides, and layer thicknesses using one consistent length unit.
3. Enter area deductions
Add glue lines, fold allowance, trimming, tube attachment, inactive margins, and manufacturing waste.
4. Set the production target
Enter permeate flow directly or derive permeate from feed flow multiplied by system recovery.
5. Apply design corrections
Review temperature, fouling, decline, availability, operating hours, safety factor, and pressure assumptions.
6. Review configuration
Check element count, vessels, stage allocation, area margin, flux, net driving pressure, and warning messages.
Formula reference
Core relationships used by the calculator.
Gross and effective membrane area
Here, U is the usable-area factor. W is the manufacturing-waste fraction.
Required process area
Qp is permeate flow in m³/day. J is flux in LMH. HF is operating hours divided by 24. AF is plant availability.
Element and vessel quantities
Recovery and flow balance
Net driving pressure
Theoretical spiral wrap estimate
Membrane technology guidance
Editable screening ranges help identify unusual assumptions.
| Technology | Typical flux range | Typical recovery range | Common design focus |
|---|---|---|---|
| Brackish-water RO | 12–28 LMH | 50–85% | Scaling, recovery, salt passage, lead-element flux |
| Seawater RO | 8–18 LMH | 30–50% | Osmotic pressure, energy recovery, boron, intake fouling |
| Nanofiltration | 15–35 LMH | 60–90% | Hardness removal, organics, selective ion rejection |
| Ultrafiltration | 30–100 LMH | 85–98% | Backwash, chemically enhanced cleaning, solids loading |
| Microfiltration | 50–180 LMH | 85–99% | Backwash, air scour, transmembrane pressure |
| Forward osmosis | 5–25 LMH | 20–80% | Draw solution, reverse salt flux, internal concentration polarization |
Ranges are broad screening values. Final selections must follow current manufacturer limits and project-specific feed-water analysis.
Design notes and limitations
Important boundaries for responsible use.
Geometry does not replace hydraulic projection
Membrane area alone cannot confirm acceptable pressure drop. It also cannot confirm concentration polarization, scaling tendency, or permeate quality. A vendor projection should be completed before procurement.
Active area varies by manufacturer
Published active area may use proprietary measurement conventions. Sheet deductions, leaf construction, and spacer designs differ. Use the current element datasheet as the governing source.
Flux must match feed-water risk
Clean municipal water may tolerate a different flux than wastewater reuse. Pretreatment reliability, silt density, organics, microbiology, and cleaning frequency should shape the selected design flux.
Recovery is an array property
Recovery should be checked by stage and vessel. High overall recovery may create excessive tail-element concentration. Scaling calculations and minimum concentrate flow checks remain necessary.
Spiral-pack calculations are theoretical
Actual winding includes compression, adhesive thickness, overlap, anti-telescoping devices, and fabrication tolerance. The wrap estimate is useful for screening, not manufacturing drawings.
Pressure model is intentionally simplified
The net driving pressure check uses average feed pressure and one osmotic-pressure value. Detailed projections use element-by-element concentration, pressure, temperature, salt passage, and flow relationships.