function validateInput(input) {
if (input.value < 0) input.value = 0;
}
function calculateROFlux() {
// 1. Get input values
var flowGPM = parseFloat(document.getElementById('permFlow').value);
var numMembranes = parseInt(document.getElementById('numMembranes').value);
var areaFt2 = parseFloat(document.getElementById('areaPerMembrane').value);
// 2. Validation
if (isNaN(flowGPM) || isNaN(numMembranes) || isNaN(areaFt2) || numMembranes <= 0 || areaFt2 <= 0) {
alert("Please enter valid positive numbers for flow, element count, and surface area.");
return;
}
// 3. Perform Calculations
// Calculate Total Gallons Per Day (GPD) = GPM * 1440 mins/day
var gpd = flowGPM * 1440;
// Calculate Total Active Surface Area (ft²)
var totalArea = numMembranes * areaFt2;
// Calculate Flux in GFD (Gallons per Square Foot per Day)
var fluxGFD = gpd / totalArea;
// Calculate Flux in LMH (Liters per Square Meter per Hour)
// Conversion: 1 GFD = 1.69901 LMH
var fluxLMH = fluxGFD * 1.69901;
// 4. Update UI
document.getElementById('resGFD').innerText = fluxGFD.toFixed(2) + " gal/ft²/day";
document.getElementById('resLMH').innerText = fluxLMH.toFixed(2) + " L/m²/h";
document.getElementById('resTotalArea').innerText = totalArea.toLocaleString() + " ft²";
document.getElementById('resGPD').innerText = gpd.toLocaleString() + " gal/day";
// 5. Status Logic (General guidelines for Brackish Water RO)
var statusDiv = document.getElementById('statusMessage');
var message = "";
statusDiv.className = "ro-status"; // Reset classes
if (fluxGFD = 10 && fluxGFD <= 18) {
statusDiv.classList.add("status-optimal");
message = "Optimal Range: Typical for brackish water RO systems.";
} else {
statusDiv.classList.add("status-high");
message = "High Flux: Increased risk of membrane fouling and scaling. Monitor differential pressure closely.";
}
statusDiv.innerText = message;
document.getElementById('roResult').style.display = 'block';
}
Understanding RO Flux Rate
In the context of Reverse Osmosis (RO) water treatment, Flux is one of the most critical design and operating parameters. It is defined as the volume of permeate (filtered water) passing through a unit area of membrane per unit of time.
Calculating the flux rate allows operators and engineers to determine how hard the membranes are working. A system designed with an excessively high flux rate is prone to rapid fouling and scaling, leading to frequent cleaning (CIP) and shortened membrane life. Conversely, an excessively low flux rate implies the system is oversized, resulting in unnecessary capital expenditure on pressure vessels and elements.
The Flux Formula
The standard equation for calculating RO flux involves normalizing the permeate flow rate against the total active surface area of the membranes installed in the system.
Flux (GFD) = Total Permeate Flow (GPD) / Total Active Membrane Area (ft²)
Where:
GFD: Gallons per Square Foot per Day.
GPD: Gallons per Day (calculated as GPM × 1440).
Active Area: The specific surface area of the membrane elements (e.g., a standard 8040 element often has 400 ft² or 37.2 m²).
Typical Flux Guidelines by Water Source
The acceptable flux rate depends heavily on the quality of the feed water. Water with higher Silt Density Index (SDI) or fouling potential requires a lower design flux to maintain stable operation.
Feed Water Source
Typical Flux Range (GFD)
Typical Flux Range (LMH)
Surface Water (High fouling)
8 – 12
14 – 20
Wastewater / Effluent
10 – 14
17 – 24
Brackish Well Water
14 – 18
24 – 30
Seawater (SWRO)
7 – 10
12 – 17
Permeate (2nd Pass RO)
20 – 30
34 – 51
Why Monitor Flux?
1. Fouling Control: High flux pulls contaminants toward the membrane surface faster than cross-flow velocity can sweep them away, leading to concentration polarization and fouling layer formation.
2. Energy Efficiency: Operating at optimal flux ensures the system runs within the efficient range of the high-pressure pump curves.
3. Membrane Lifespan: Consistent operation within recommended flux guidelines (usually below 16-18 GFD for standard brackish water) prevents irreversible physical damage to the membrane leaves.