Calculate normalized permeate flow from actual flow, temperatures, and feed/permeate pressures, or solve the related missing variable.

Simplified estimate: assumes negligible osmotic pressure and feed-channel pressure loss. FilmTec empirical TCF; follow your membraneโ€™s operating limits.

Related Calculators

Normalized Permeate Flow Formula

The calculator estimates permeate-flow normalization using the FilmTec empirical temperature correction and a feed-minus-permeate pressure ratio. It assumes negligible osmotic pressure and feed-channel pressure loss; this pressure difference is not the full RO net driving pressure. Use the membrane manufacturerโ€™s full normalization method for system monitoring.

NPF = APF ร— (TCFโ‚› / TCFโ‚) ร— ((Pfs - Pโ‚šs) / (Pfa - Pโ‚ša))
TCF(T) = exp(C ร— (1 / 298 - 1 / (273 + T))); C = 3020 below 25 ยฐC, 2640 at or above 25 ยฐC
  • NPF = normalized permeate flow
  • APF = actual permeate flow
  • TCFs = temperature correction factor at the standard temperature
  • TCFa = temperature correction factor at the actual temperature
  • T = temperature in ยฐC
  • Pfs = standard feed pressure
  • Pps = standard permeate pressure
  • Pfa = actual feed pressure
  • Ppa = actual permeate pressure
  • Pfs - Pps = standard pressure difference
  • Pfa - Ppa = actual pressure difference

If normalized permeate flow is the missing value, the calculator applies the main formula directly. If actual permeate flow is missing, it rearranges the same formula:

APF = NPF ร— (TCFโ‚ / TCFโ‚›) ร— ((Pfa - Pโ‚ša) / (Pfs - Pโ‚šs))

If a temperature is missing, the calculator first solves for the needed TCF value, then converts that TCF back to temperature. If one pressure is missing, it solves for the required pressure difference first, then adds or subtracts the known pressure.

Reference Values for Units and Temperature Correction

The calculator converts entered values to base units before calculating: L/s for flow, ยฐC for temperature, and psi for pressure.

Quantity Unit Base-unit conversion
Flow 1 GPM 0.0630902 L/s
Flow 1 mยณ/h 0.2777778 L/s
Pressure 1 bar 14.5038 psi
Pressure 1 kPa 0.145038 psi

Temperature Approximate TCF Effect on permeate flow normalization
10 ยฐC 0.584 Cold water gives a lower TCF.
15 ยฐC 0.703 Flow is corrected upward when compared with 25 ยฐC.
20 ยฐC 0.841 Moderate correction below 25 ยฐC.
25 ยฐC 1.000 Reference point for this TCF equation.
30 ยฐC 1.157 Warm water gives a higher TCF.

Example Calculations

Example 1: Calculate normalized permeate flow

Suppose the actual permeate flow is 10 GPM, the standard temperature is 25 ยฐC, and the actual temperature is 20 ยฐC. The actual feed pressure is 200 psi, actual permeate pressure is 10 psi, standard feed pressure is 180 psi, and standard permeate pressure is 10 psi.

NPF = 10 ร— (1.000 / 0.841) ร— ((180 - 10) / (200 - 10))
NPF = 10.64 GPM (using the unrounded TCF)

Example 2: Calculate actual permeate flow

Suppose the normalized permeate flow is 12 L/s, the standard temperature is 25 ยฐC, and the actual temperature is 30 ยฐC. The actual feed pressure is 16 bar, actual permeate pressure is 1 bar, standard feed pressure is 14 bar, and standard permeate pressure is 1 bar.

APF = 12 ร— (1.157 / 1.000) ร— ((16 - 1) / (14 - 1))
APF = 16.03 L / s (using the unrounded TCF)

FAQ

What does normalized permeate flow tell you?

Full manufacturer-normalized flow can help track performance at common reference conditions. This calculatorโ€™s simplified estimate omits osmotic pressure and channel losses, so changes in salinity or those losses can affect it. A downward trend in this estimate alone does not establish fouling, scaling or compaction.

Why do feed pressure and permeate pressure both matter?

The calculator uses the pressure difference across the membrane, not feed pressure alone. A higher permeate backpressure reduces the effective driving pressure. That is why the formula uses Pf - Pp for both actual and standard conditions.

Why might this result differ from a membrane manufacturerโ€™s normalization sheet?

This calculator uses a simplified pressure and temperature correction. Some manufacturer methods also correct for osmotic pressure, feed concentration, recovery, membrane area, element age, and specific membrane chemistry. For formal system monitoring, use the normalization method specified for the membrane and RO system.