function calculateDryingRate() {
// Get Input Values
var wInitial = document.getElementById('initialWeight').value;
var wFinal = document.getElementById('finalWeight').value;
var tTime = document.getElementById('timeElapsed').value;
var sArea = document.getElementById('surfaceArea').value;
var errorDiv = document.getElementById('errorMsg');
var resultDiv = document.getElementById('results');
// Reset display
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
// Convert to floats
var w1 = parseFloat(wInitial);
var w2 = parseFloat(wFinal);
var t = parseFloat(tTime);
var a = parseFloat(sArea);
// Validation Logic
if (isNaN(w1) || isNaN(w2) || isNaN(t) || isNaN(a)) {
errorDiv.innerHTML = "Please fill in all fields with valid numbers.";
errorDiv.style.display = 'block';
return;
}
if (t <= 0) {
errorDiv.innerHTML = "Time elapsed must be greater than zero.";
errorDiv.style.display = 'block';
return;
}
if (a w1) {
errorDiv.innerHTML = "Final weight cannot be greater than initial weight (this implies weight gain).";
errorDiv.style.display = 'block';
return;
}
// Calculations
// Moisture Removed (kg)
var moistureRemoved = w1 – w2;
// Drying Rate Formula: R = dW / (A * dt)
// Rate (kg/m²/h)
var dryingRate = moistureRemoved / (a * t);
// Percentage Loss based on initial weight
var percentLoss = (moistureRemoved / w1) * 100;
// Update DOM
document.getElementById('rateResult').innerHTML = dryingRate.toFixed(4) + " kg/m²/h";
document.getElementById('moistureResult').innerHTML = moistureRemoved.toFixed(3) + " kg";
document.getElementById('percentResult').innerHTML = percentLoss.toFixed(2) + "%";
// Show Results
resultDiv.style.display = 'block';
}
Understanding Drying Rate Calculations
In industrial processing, chemical engineering, and food technology, determining the drying rate is crucial for optimizing energy efficiency and ensuring product quality. This calculator assists engineers and operators in quantifying the speed at which moisture is removed from a solid material over a specific surface area.
The Drying Rate Formula
The drying rate ($R$) represents the mass of moisture removed per unit of time per unit of surface area. It is generally calculated using the following equation:
R = (W_initial – W_final) / (A × t)
W_initial: The weight of the wet material at the start of the interval (kg).
W_final: The weight of the material at the end of the interval (kg).
A: The surface area available for drying (m²).
t: The time elapsed during the drying interval (hours).
Phases of Drying
Drying does not occur at a uniform speed. It typically follows specific phases that affect the calculation interpretation:
Constant Rate Period: In this initial phase, the surface of the solid is fully saturated with liquid. Evaporation occurs as if from a free liquid surface. The rate ($R$) remains relatively constant as long as external conditions (temperature, humidity, air velocity) remain stable.
Falling Rate Period: Once the surface moisture is depleted (reaching the "Critical Moisture Content"), the drying rate begins to decrease. The limiting factor shifts from surface evaporation to the internal diffusion of moisture from the core of the solid to the surface.
Why Surface Area Matters
The efficiency of most dryers—whether tray dryers, tunnel dryers, or solar dryers—depends heavily on the surface area exposed to the heating medium (usually air). Spreading material thinly increases the surface area ($A$) relative to the volume, significantly increasing the drying rate and reducing total processing time.
Practical Applications
This calculation is widely used in:
Food Preservation: Calculating dehydration rates for fruits, vegetables, and meats to prevent spoilage.
Pharmaceuticals: Ensuring precise moisture content in tablet granulation processes.
Ceramics and Timber: Managing drying schedules to prevent cracking or warping due to uneven moisture loss.
By monitoring the drying rate, operators can adjust temperature and airflow to transition efficiently from the constant rate period to the falling rate period, minimizing energy costs.