function calculateN2Flow() {
// Get Inputs
var vesselVolume = parseFloat(document.getElementById('vesselVolume').value);
var volumeUnit = document.getElementById('volumeUnit').value;
var currentO2 = parseFloat(document.getElementById('currentO2').value);
var targetO2 = parseFloat(document.getElementById('targetO2').value);
var purgeTime = parseFloat(document.getElementById('purgeTime').value);
// Error Elements
var errorDiv = document.getElementById('errorMessage');
var resultsDiv = document.getElementById('n2Results');
// Reset display
errorDiv.style.display = 'none';
errorDiv.innerText = ";
resultsDiv.style.display = 'none';
// Validation
if (isNaN(vesselVolume) || vesselVolume = currentO2) {
errorDiv.innerText = "Target Oxygen must be lower than Current Oxygen for inerting.";
errorDiv.style.display = 'block';
return;
}
if (targetO2 <= 0) {
errorDiv.innerText = "Target Oxygen must be greater than 0% for logarithmic calculation.";
errorDiv.style.display = 'block';
return;
}
if (isNaN(purgeTime) || purgeTime <= 0) {
errorDiv.innerText = "Please enter a valid purge time in minutes.";
errorDiv.style.display = 'block';
return;
}
// 1. Normalize Volume to Cubic Meters (m3)
var volInM3 = 0;
if (volumeUnit === 'm3') {
volInM3 = vesselVolume;
} else if (volumeUnit === 'ft3') {
volInM3 = vesselVolume / 35.3147;
} else if (volumeUnit === 'liters') {
volInM3 = vesselVolume / 1000;
} else if (volumeUnit === 'gallons') {
volInM3 = vesselVolume / 264.172;
}
// 2. Calculate Number of Volume Exchanges (Cycles) using Dilution Formula
// Formula: n = ln(C_initial / C_final)
// Note: We use ratio of O2. Assuming pure N2 injection (0% O2 in N2 source).
var cycles = Math.log(currentO2 / targetO2);
// 3. Calculate Total Required N2 Volume (in m3)
var totalN2_m3 = volInM3 * cycles;
// 4. Calculate Flow Rates
// Flow Rate = Total Volume / Time
var flowRate_m3_min = totalN2_m3 / purgeTime;
var flowRate_m3_hr = flowRate_m3_min * 60;
// Conversions
// 1 m3/hr = 0.588578 SCFM
var flowRate_scfm = flowRate_m3_hr * 0.588578;
// 1 m3/min = 1000 L/min
var flowRate_l_min = flowRate_m3_min * 1000;
// Display Unit formatting for Total Volume based on input
var displayTotalVol = "";
if (volumeUnit === 'm3' || volumeUnit === 'liters') {
displayTotalVol = totalN2_m3.toFixed(2) + " m³";
} else {
displayTotalVol = (totalN2_m3 * 35.3147).toFixed(2) + " ft³";
}
// Output Results
document.getElementById('resCycles').innerText = cycles.toFixed(2);
document.getElementById('resTotalVol').innerText = displayTotalVol;
document.getElementById('resFlowM3h').innerText = flowRate_m3_hr.toFixed(2);
document.getElementById('resFlowSCFM').innerText = flowRate_scfm.toFixed(2);
document.getElementById('resFlowLmin').innerText = flowRate_l_min.toFixed(2);
resultsDiv.style.display = 'block';
}
Understanding Nitrogen Flow Rate for Inerting
The Nitrogen (N2) Flow Rate Calculator is designed for engineers and technicians involved in tank blanketing, pipeline purging, and equipment inerting. The primary goal of these operations is to reduce the oxygen concentration within a vessel to a safe level to prevent combustion or oxidation.
This calculator determines the flow rate required to replace the internal atmosphere of a vessel with nitrogen within a specific timeframe using the Dilution Purging method.
The Purging Formula
To calculate the amount of nitrogen required to lower oxygen levels, we use the logarithmic dilution formula, which assumes that the incoming nitrogen mixes perfectly with the existing gas in the vessel.
n = ln( C_initial / C_final )
n: The number of volume exchanges (cycles) required.
C_initial: The starting oxygen concentration (usually 20.9% for air).
C_final: The target oxygen concentration (e.g., 4% for LEL safety, or lower for quality).
Once the number of exchanges is known, the total volume of nitrogen is calculated as:
Total N2 Volume = Vessel Volume × n
Finally, the Flow Rate is derived by dividing the total required volume by the desired time duration for the operation.
Why is N2 Flow Rate Important?
Safety: Ensuring the flow rate is sufficient to lower oxygen levels below the Limiting Oxygen Concentration (LOC) prevents explosions in hazardous environments.
Efficiency: Calculating the exact flow rate prevents the waste of expensive nitrogen gas by avoiding excessive purging.
Time Management: Knowing the flow rate helps in planning maintenance schedules by predicting exactly how long an inerting process will take.
Frequently Asked Questions
What is the difference between displacement and dilution purging?
Dilution purging involves mixing the nitrogen with the tank's atmosphere and venting the mixture. Displacement purging involves pushing the old gas out with nitrogen with minimal mixing (plug flow). This calculator uses the dilution method, which is generally more conservative and common for irregular vessel shapes.
What is SCFM?
SCFM stands for Standard Cubic Feet per Minute. It is a volumetric flow rate corrected to standardized conditions of temperature and pressure, making it a reliable metric for gas mass flow comparisons.
Does temperature affect the calculation?
Yes, gas volume changes with temperature (Charles's Law). However, for general estimation purposes, this calculator assumes standard ambient conditions. If you are purging at very high temperatures or pressures, additional correction factors based on the Ideal Gas Law are necessary.
How much nitrogen do I need to reach 1% Oxygen?
Starting from air (20.9%), reaching 1% oxygen typically requires approximately 3.04 volume exchanges using the dilution method.