Ethanol Evaporation Rate Calculator
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Ethanol Evaporation Rate Calculator
Calculated Results
Evaporation Rate (Mass)
–
0 g/min
Vapor Pressure (Estimated)
–
Based on Antoine Equation
Total Ethanol Lost
–
0 Liters
Note: This calculator uses the Antoine equation for vapor pressure and a mass transfer coefficient model based on air velocity. Actual rates may vary depending on relative humidity and container geometry.
function calculateEvaporation() {
// Get Inputs
var area = parseFloat(document.getElementById('surfaceArea').value);
var tempC = parseFloat(document.getElementById('liquidTemp').value);
var velocity = parseFloat(document.getElementById('airVelocity').value);
var hours = parseFloat(document.getElementById('exposureTime').value);
// Validation
if (isNaN(area) || isNaN(tempC) || isNaN(velocity) || isNaN(hours)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (tempC >= 78.4) {
alert("Temperature is above Ethanol boiling point (78.37°C). Evaporation is no longer the primary mechanism (Boiling). Calculation limited.");
tempC = 78.3; // Cap slightly below boiling for math stability
}
// Constants for Ethanol (C2H5OH)
var molWeight = 46.07; // g/mol
var density = 789; // kg/m3 at 20C (approx)
var gasConstant = 8.314; // J/(mol*K)
var tempK = tempC + 273.15; // Kelvin
// 1. Calculate Vapor Pressure using Antoine Equation
// log10(P_mmHg) = A – (B / (C + T_degC))
// Constants for Ethanol:
var A = 8.04494;
var B = 1554.3;
var C = 222.65;
var logP_mmHg = A – (B / (C + tempC));
var P_mmHg = Math.pow(10, logP_mmHg);
var P_Pa = P_mmHg * 133.322; // Convert mmHg to Pascals
// 2. Mass Transfer Coefficient (Km) in m/s
// Empirical estimation: Km varies significantly with airflow.
// Still air ~ 0.002 m/s.
// Windy conditions ~ 0.005 to 0.01 m/s.
// Formula approximation: Km = 0.002 + (0.004 * velocity)
var Km = 0.002 + (0.004 * velocity);
// 3. Evaporation Rate Calculation (Mass Transfer Model)
// E = (M * Km * Area * P_vap) / (R * T)
// Units:
// M (kg/mol) = 0.04607
// Km (m/s)
// Area (m2)
// P_vap (Pa)
// R (J/mol K)
// T (K)
// Result E is in kg/s
var molWeightKg = molWeight / 1000; // 0.04607 kg/mol
var evapRateKgPerSec = (molWeightKg * Km * area * P_Pa) / (gasConstant * tempK);
// Convert Rate to user friendly units
var evapRateKgPerHr = evapRateKgPerSec * 3600;
var evapRateGPerMin = (evapRateKgPerSec * 1000) * 60;
// Calculate Totals over time
var totalMassLostKg = evapRateKgPerHr * hours;
var totalVolLostLiters = (totalMassLostKg / (density / 1000)); // Density is kg/m3, /1000 for kg/L
// Formatting Results
document.getElementById('rateKgHr').innerHTML = evapRateKgPerHr.toFixed(3) + " kg/hr";
document.getElementById('rateGMin').innerHTML = evapRateGPerMin.toFixed(2) + " g/min";
document.getElementById('vaporPressure').innerHTML = (P_Pa / 1000).toFixed(2) + " kPa (" + P_mmHg.toFixed(1) + " mmHg)";
document.getElementById('totalLossMass').innerHTML = totalMassLostKg.toFixed(3) + " kg";
document.getElementById('totalLossVol').innerHTML = totalVolLostLiters.toFixed(2) + " Liters";
}
Understanding Ethanol Evaporation Dynamics
Ethanol (Ethyl Alcohol) is a volatile organic compound widely used in laboratories, industrial cleaning, and distillation processes. Understanding the rate at which ethanol evaporates is crucial for safety compliance, process efficiency, and inventory management. This calculator estimates the evaporation rate based on surface area, temperature, and airflow velocity.
Key Factors Influencing Evaporation
The rate at which ethanol transitions from liquid to gas depends on three primary variables:
- Vapor Pressure: This is temperature-dependent. As the temperature of the liquid rises, the molecules move faster and escape the surface more easily. At 20°C, ethanol has a vapor pressure of roughly 5.95 kPa, but this rises sharply as it approaches its boiling point of 78.37°C.
- Surface Area: Evaporation is a surface phenomenon. A wide, shallow pan of ethanol will evaporate significantly faster than the same volume in a narrow beaker because there is more interface for molecules to escape.
- Airflow (Mass Transfer): If the air above the liquid is still, it becomes saturated with ethanol vapor, slowing down further evaporation. Airflow (ventilation, fume hoods, or wind) strips this saturated layer away, maintaining a concentration gradient that accelerates evaporation.
The Mathematics Behind the Calculation
This calculator utilizes a mass transfer model combined with the Antoine Equation to determine the vapor pressure of ethanol at a specific temperature.
Antoine Equation used:
log10(P) = A – [B / (C + T)]
Where P is pressure in mmHg and T is temperature in Celsius.
Once the vapor pressure is determined, the evaporation rate (E) is estimated using a mass transfer coefficient ($K_m$) which adjusts based on your input for air velocity. The simplified formula for the rate in kg/s is derived from:
Rate = (M × Km × A × Pvap) / (R × T)
Where M is the molar mass of ethanol, A is surface area, R is the ideal gas constant, and T is the temperature in Kelvin.
Safety Considerations
Ethanol vapor is flammable and heavier than air. Rapid evaporation in a poorly ventilated space can lead to the accumulation of vapors near the floor, creating an explosion hazard or health risks for inhalation. Always ensure that the calculated evaporation rate does not exceed the ventilation capacity of your workspace (e.g., fume hood limits).
Common Vapor Pressures of Ethanol
| Temperature (°C) |
Vapor Pressure (kPa) |
Evaporation Potential |
| 0°C |
1.6 |
Low |
| 20°C |
5.9 |
Moderate |
| 40°C |
17.8 |
High |
| 60°C |
47.0 |
Very High |
| 78.4°C |
101.3 |
Boiling |