Osmotic Pressure and Membrane Driving Force: Hydraulic Pressure Alone Is Incomplete

Define the Interface or Transport Basis

Hydranautics' TAB114, equations 2–4 relates permeate flux to permeability and net driving pressure, after subtracting the osmotic difference from the stated average hydraulic pressure difference. The opposing osmotic contribution therefore belongs in a net-driving-pressure review; hydraulic TMP alone does not identify it.

Review a Hypothetical Comparison

Assume an invented hydraulic difference of 12 bar and an osmotic difference of 8 bar across the defined membrane boundary. Net driving difference is 4 bar. If a second state has the same hydraulic difference but an osmotic difference of 10 bar, the net term is 2 bar. With the deliberately held-constant permeability and area of this illustration, the model would give half the permeation flow. No real membrane permeability or process limit is assigned.

Keep the Evidence with the Decision

Keep the hydraulic pressures, osmotic states and spatial averaging basis together. Check whether the model uses feed, local surface or average concentrate conditions. If concentration polarization changes local composition, do not substitute a bulk value without explaining it. Reassess permeability and other assumptions before treating a change in net difference as a measured flow prediction.

This is a model-boundary worksheet, not a reverse-osmosis design or pressure setpoint. It also does not turn a membrane-module TMP calculation into an osmotic-pressure measurement.

What net driving difference remains after the stated osmotic contribution?

This blank worksheet is for your own project. It contains no H M machine trial result.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Hydranautics' TAB114, equations 2–4
• Reference from hmpharmamachines.com