.he-calculator-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
}
.he-calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.he-calc-grid {
grid-template-columns: 1fr;
}
}
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margin-bottom: 15px;
}
.he-input-group label {
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.he-input-group input {
width: 100%;
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border: none;
border-radius: 4px;
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font-weight: bold;
cursor: pointer;
margin-top: 10px;
transition: background-color 0.2s;
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.he-btn:hover {
background-color: #004494;
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padding: 20px;
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.he-content h2 {
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How to Calculate Mass Flow Rate in a Heat Exchanger
Calculating the mass flow rate is a fundamental step in designing and analyzing heat exchangers. Whether you are working with shell-and-tube exchangers, plate exchangers, or simple air cooling systems, understanding the relationship between heat energy, temperature change, and fluid properties is essential for ensuring thermal efficiency.
The Fundamental Energy Balance Equation
The calculation of mass flow rate relies on the First Law of Thermodynamics, specifically the energy balance equation for a steady-flow open system. Assuming no phase change occurs (e.g., the fluid remains liquid or gas throughout), the formula relates the heat duty to the mass flow.
The Formula:
Q = m × Cp × ΔT
Where:
- Q = Heat Transfer Rate (kW or kJ/s)
- m = Mass Flow Rate (kg/s)
- Cp = Specific Heat Capacity of the fluid (kJ/kg·°C)
- ΔT = Temperature difference between inlet and outlet (|T_in – T_out|) in °C
Rearranging to Find Mass Flow Rate (m)
To solve for the mass flow rate, we rearrange the equation as follows:
m = Q / (Cp × ΔT)
Step-by-Step Calculation Guide
- Determine the Heat Load (Q): This is the amount of energy that must be added or removed from the fluid, usually measured in Kilowatts (kW).
- Identify the Fluid Properties (Cp): Find the specific heat capacity of your working fluid. For water at standard conditions, this is approximately 4.18 kJ/kg·°C. For oils or air, this value will differ significantly.
- Measure Temperatures: Record the Inlet Temperature (T_in) and the required Outlet Temperature (T_out).
- Calculate ΔT: Subtract the smaller temperature from the larger one to find the absolute difference.
- Compute: Divide Q by the product of Cp and ΔT.
Realistic Example Calculation
Let's assume you have a process water loop that needs to be cooled.
| Variable |
Value |
| Heat Load (Q) |
500 kW |
| Fluid |
Water |
| Specific Heat (Cp) |
4.186 kJ/kg·°C |
| Inlet Temp (T_in) |
45°C |
| Outlet Temp (T_out) |
35°C |
1. Calculate ΔT: 45°C – 35°C = 10°C
2. Apply Formula: m = 500 / (4.186 × 10)
3. Result: m = 500 / 41.86 ≈ 11.94 kg/s
To convert this to kilograms per hour, multiply by 3600 (seconds in an hour):
11.94 kg/s × 3600 = 42,984 kg/hr.
Why is Mass Flow Rate Important?
If the mass flow rate is too low, the fluid may exit the heat exchanger at a temperature that is too high (in cooling applications) or too low (in heating applications), potentially damaging downstream equipment. Conversely, an excessively high flow rate increases the pressure drop across the exchanger, requiring larger pumps and consuming more electrical energy, which reduces overall system efficiency.
function calculateMassFlow() {
// Get input elements using var
var inputQ = document.getElementById('he_heat_transfer');
var inputCp = document.getElementById('he_specific_heat');
var inputTin = document.getElementById('he_temp_in');
var inputTout = document.getElementById('he_temp_out');
var resultBox = document.getElementById('he_results_box');
var errorBox = document.getElementById('he_error_msg');
// Parse values
var qVal = parseFloat(inputQ.value);
var cpVal = parseFloat(inputCp.value);
var tInVal = parseFloat(inputTin.value);
var tOutVal = parseFloat(inputTout.value);
// Reset display
errorBox.style.display = 'none';
resultBox.style.display = 'none';
// Validation
if (isNaN(qVal) || isNaN(cpVal) || isNaN(tInVal) || isNaN(tOutVal)) {
errorBox.innerText = "Please fill in all fields with valid numbers.";
errorBox.style.display = 'block';
return;
}
if (cpVal <= 0) {
errorBox.innerText = "Specific Heat Capacity must be greater than zero.";
errorBox.style.display = 'block';
return;
}
// Calculate Temperature Difference
var deltaT = Math.abs(tInVal – tOutVal);
if (deltaT === 0) {
errorBox.innerText = "Inlet and Outlet temperatures cannot be the same (ΔT = 0). Mass flow would be infinite.";
errorBox.style.display = 'block';
return;
}
// Calculate Mass Flow Rate (kg/s)
// Formula: m = Q / (Cp * dT)
// Check units: kW / (kJ/kg*C * C) = (kJ/s) / (kJ/kg) = kg/s. Correct.
var massFlowSec = qVal / (cpVal * deltaT);
// Calculate Mass Flow Rate (kg/hr)
var massFlowHour = massFlowSec * 3600;
// Display Results
document.getElementById('res_delta_t').innerText = deltaT.toFixed(2);
document.getElementById('res_flow_s').innerText = massFlowSec.toFixed(4);
document.getElementById('res_flow_h').innerText = massFlowHour.toFixed(2);
resultBox.style.display = 'block';
}