Reverse Osmosis Net Driving Pressure (NDP) Calculator
Calculate feed-concentrate average osmotic pressure, Net Driving Pressure (NDP), temperature correction factor (TCF), and normalized permeate flux per ASTM D4516.
Hydraulic Pressures & Permeate
Salinity & Temperature State
Net Driving Pressure & Osmotic Forces
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
What is Net Driving Pressure (NDP) in reverse osmosis systems?
NDP is the actual effective net pressure driving pure water molecules across the semi-permeable polyamide membrane barrier. It equals the average hydraulic feed pressure minus the permeate backpressure, minus the counteracting osmotic pressure of the concentrated salt solution: NDP = (Pavg - Pp) - (pi_fc - pi_p).
Why is the Temperature Correction Factor (TCF) essential for RO performance tracking?
Water viscosity changes significantly with temperature: cold water (10°C) is roughly 40% more viscous than warm water (25°C). Without temperature normalization via TCF = exp(2640 * (1/298.15 - 1/T)), an operator might mistake seasonal winter water cooling for catastrophic membrane fouling.
How does system recovery percentage directly increase osmotic pressure?
As water permeates across the membrane, salts are retained in the brine stream. At 75% recovery, the concentrate TDS is 4× higher than feed TDS (1 / (1 - 0.75)). This elevated salinity drastically raises osmotic backpressure (pi ~ 1 psi per 100 ppm TDS), reducing NDP and requiring higher pump discharge pressures.