Membrane Flux Calculator

This calculator derives permeate flux and its downstream indicators from feed flow, membrane area, transmembrane pressure (TMP), and recovery rate. Permeate Flux itself moves with three inputs at roughly comparable strength -- Total Membrane Area (larger area spreads the same permeate flow over more surface, lowering flux per unit area), Feed Flow Rate, and Recovery Rate -- so no single one of those three dominates the others. Specific Flux and Permeability are reported as separate outputs but are numerically identical: both are defined as flux divided by TMP (LMH/bar), which is the standard engineering definition of membrane permeability, not two independent measurements that happen to coincide. Concentration Factor is driven almost entirely by Recovery Rate, since recovery directly sets what fraction of feed water leaves as permeate versus concentrate and nothing else appears in that formula. Concentrate Flow depends on both Recovery Rate and Feed Flow Rate, but because Feed Flow Rate's declared range spans a much wider ratio (0.01-100 MGD) than Recovery Rate's (30-99%), Feed Flow Rate is actually the input Concentrate Flow moves the most across their full ranges, even though Recovery Rate sets what fraction of any given feed flow ends up as concentrate.

Specific Energy, by contrast, is driven mostly by Transmembrane Pressure and, to a smaller but real degree, Recovery Rate -- because pumping energy scales with flow times pressure while Specific Energy is energy per unit of PERMEATE volume, the feed-flow-rate terms cancel out of the ratio entirely, but Recovery Rate stays in the denominator (a higher recovery rate spreads the same pumping energy over more permeate, lowering Specific Energy). Transmembrane Pressure's 800x declared-range span (0.1-80 bar) swings Specific Energy far more than Recovery Rate's roughly 3x span (30-99%) does, so TMP remains the dominant driver, just not the only one. Membrane Modules, Pressure Vessels, and Annual Membrane Cost are all set by Total Membrane Area alone, based on a fixed typical module size and per-module replacement cost. This calculator uses industry rule-of-thumb figures for module size, pump efficiency, and replacement cost/interval rather than a specific vendor's equipment specs -- confirm actual figures against your membrane manufacturer's documentation before finalizing a system design.