Calculate the required mass and volumetric flow rate for industrial cooling applications.
Default for water is 4.186 kJ/kg·°C
Calculation Results:
Mass Flow Rate: kg/s
Volumetric Flow Rate: m³/hr
Flow Rate in Liters per Minute: LPM
Understanding Cooling Water Flow Rate in Heat Exchangers
In thermal engineering, calculating the correct cooling water flow rate is critical for maintaining equipment safety and process efficiency. A heat exchanger transfers thermal energy from a "hot" fluid to a "cold" fluid (typically water) through a conductive barrier. If the flow rate is too low, the system may overheat; if it is too high, you waste pumping energy and risk erosion-corrosion in the piping.
The Fundamental Heat Transfer Equation
The calculation is based on the principle of energy conservation. The heat absorbed by the cooling water must equal the heat rejected by the process (assuming negligible ambient losses). The formula used is:
Q = ṁ × Cp × ΔT
Where:
Q: Heat load or heat transfer rate (kW or kJ/s).
ṁ (m-dot): Mass flow rate of the cooling water (kg/s).
Cp: Specific heat capacity of water (approx. 4.186 kJ/kg·°C).
ΔT: Temperature rise of the water (T_outlet – T_inlet).
Step-by-Step Calculation Example
Imagine a hydraulic power unit that generates 150 kW of waste heat. You want to cool it using water entering at 20°C and exiting at 30°C.
Determine Heat Load (Q): 150 kW.
Determine Temperature Difference (ΔT): 30°C – 20°C = 10°C.
Convert to Volumetric Flow: Since 1 kg of water is approximately 1 liter, the flow is 3.58 L/s or 214.8 Liters Per Minute (LPM).
Factors Affecting Cooling Requirements
While the basic formula provides the theoretical requirement, real-world applications must consider:
Fouling Factor: Over time, mineral deposits or biological growth inside the heat exchanger tubes act as an insulator, reducing efficiency. Engineers often "over-size" the flow rate to account for this.
Pressure Drop: Higher flow rates increase the pressure drop (resistance) across the exchanger, requiring more powerful pumps.
Approach Temperature: This is the difference between the hot fluid's outlet temperature and the cooling water's inlet temperature. A smaller approach temperature requires a significantly larger heat exchanger surface area.
Common Units Reference
In the United States, engineers often use Imperial units. The formula becomes Q (BTU/hr) = 500 × GPM × ΔT (°F). Our calculator uses the SI (Metric) standard, which is preferred in global scientific and modern industrial contexts.
function calculateFlowRate() {
var Q = parseFloat(document.getElementById("heatLoad").value);
var T1 = parseFloat(document.getElementById("tempIn").value);
var T2 = parseFloat(document.getElementById("tempOut").value);
var Cp = parseFloat(document.getElementById("specHeat").value);
var resultArea = document.getElementById("resultArea");
if (isNaN(Q) || isNaN(T1) || isNaN(T2) || isNaN(Cp)) {
alert("Please enter valid numerical values for all fields.");
return;
}
var deltaT = T2 – T1;
if (deltaT <= 0) {
alert("Outlet temperature must be higher than inlet temperature for cooling calculations.");
return;
}
// Calculation: m_dot = Q / (Cp * deltaT)
// Q in kW is kJ/s, so m_dot will be in kg/s
var massFlow = Q / (Cp * deltaT);
// Volumetric flow in m3/hr
// Density of water approx 1000 kg/m3
// m3/s = massFlow / 1000
// m3/hr = (massFlow / 1000) * 3600
var volFlowM3H = (massFlow / 1000) * 3600;
// Liters per minute
// 1 kg/s = 1 L/s = 60 LPM (approx for water)
var lpm = massFlow * 60;
document.getElementById("massFlowResult").innerText = massFlow.toFixed(3);
document.getElementById("volFlowResult").innerText = volFlowM3H.toFixed(2);
document.getElementById("lpmResult").innerText = lpm.toFixed(2);
resultArea.style.display = "block";
resultArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}