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line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
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function calculateBlowdown() {
var evapInput = document.getElementById("evaporationRate").value;
var cyclesInput = document.getElementById("cyclesOfConcentration").value;
var resultDiv = document.getElementById("result");
var errorDiv = document.getElementById("errorDisplay");
var blowdownDisplay = document.getElementById("blowdownResult");
var makeupDisplay = document.getElementById("makeupResult");
var lossDisplay = document.getElementById("lossPercent");
// Reset display
resultDiv.style.display = "none";
errorDiv.style.display = "none";
// Parsing
var E = parseFloat(evapInput);
var COC = parseFloat(cyclesInput);
// Validation
if (isNaN(E) || isNaN(COC)) {
errorDiv.innerHTML = "Please enter valid numbers for both fields.";
errorDiv.style.display = "block";
return;
}
if (E < 0) {
errorDiv.innerHTML = "Evaporation rate cannot be negative.";
errorDiv.style.display = "block";
return;
}
if (COC <= 1) {
errorDiv.innerHTML = "Cycles of Concentration must be greater than 1 to calculate blowdown.";
errorDiv.style.display = "block";
return;
}
// Calculation Logic
// Formula: B = E / (COC – 1)
var B = E / (COC – 1);
// Formula: M = E + B
var M = E + B;
// Efficiency Metric: % of makeup lost to blowdown
var percentLoss = (B / M) * 100;
// Display Results
blowdownDisplay.innerHTML = B.toFixed(2) + " units";
makeupDisplay.innerHTML = M.toFixed(2) + " units";
lossDisplay.innerHTML = percentLoss.toFixed(2) + "%";
resultDiv.style.display = "block";
}
Blowdown Rate Calculation: Optimizing Water Efficiency
Efficient water management is critical in the operation of cooling towers and boilers. The Blowdown Rate Calculator helps engineers and facility managers determine the optimal volume of water that must be removed from the system to maintain dissolved solids at acceptable levels. By balancing the Evaporation Rate with the Cycles of Concentration, operators can minimize water waste while preventing scale and corrosion.
What is Blowdown?
In cooling systems and boilers, pure water evaporates, leaving impurities (minerals and dissolved solids) behind. As evaporation continues, the concentration of these impurities increases. If left unchecked, this leads to scaling, fouling, and corrosion inside the equipment.
"Blowdown" (or bleed) is the process of intentionally discharging a portion of this concentrated water and replacing it with fresh "makeup" water. The goal is to limit the concentration of impurities to a specific threshold, known as the Cycles of Concentration.
The Blowdown Formula
To calculate the required blowdown rate, you need two primary variables: the rate at which water is evaporating from the system and the target cycles of concentration. The mathematical relationship is:
B = E / (COC – 1)
Where:
- B (Blowdown Rate): The volume of water discharged per unit of time (e.g., GPM).
- E (Evaporation Rate): The volume of water evaporating per unit of time.
- COC (Cycles of Concentration): The ratio of the concentration of dissolved solids in the blowdown water to the makeup water.
Calculating Makeup Water
Once the blowdown rate is known, the total Makeup Water (M) required by the system is simply the sum of the evaporation and the blowdown:
M = E + B
Understanding Cycles of Concentration (COC)
The Cycles of Concentration represents how concentrated the system water is compared to the inlet water. For example, if the inlet water has 100 ppm of hardness and the system water has 400 ppm, the system is operating at 4 cycles.
Higher cycles mean less blowdown and less makeup water, resulting in cost savings on water and chemicals. However, if cycles are too high, the solubility limits of minerals (like calcium and silica) may be exceeded, causing scale deposits. Finding the "sweet spot" is the key to efficient water treatment.
How to Use This Calculator
- Enter Evaporation Rate: Input the estimated evaporation rate. For cooling towers, a common rule of thumb is that evaporation equals roughly 0.1% of the recirculation rate for every 1°F of cooling range.
- Enter Cycles of Concentration: Input your target COC. This is usually determined by the water treatment chemical program and the quality of your makeup water.
- Calculate: The tool will output the necessary Blowdown Rate and the total Makeup Water required.
Example Calculation
Imagine a cooling tower with an Evaporation Rate of 100 GPM. The water treatment vendor recommends running at 5 Cycles of Concentration to prevent scaling.
Using the formula:
- B = 100 / (5 – 1)
- B = 100 / 4
- Blowdown Rate = 25 GPM
Total Makeup Water required would be 100 + 25 = 125 GPM.
Why Proper Calculation Matters
Under-blowing the system (insufficient blowdown) leads to scale formation, which reduces heat transfer efficiency and can damage equipment. Over-blowing the system (excessive blowdown) wastes water and expensive treatment chemicals. Using this calculator ensures you are operating exactly at your target parameters for maximum efficiency.