Heat Exchanger Duty Calculator Formula
Understand the math behind the heat exchanger duty calculator. Each variable explained with a worked example.
Formulas Used
Heat Duty (Q)
duty_kw = mass_flow * cp * abs(temp_in - temp_out)Heat Duty
duty_btu = mass_flow * cp * abs(temp_in - temp_out) * 3412.14Variables
| Variable | Description | Default |
|---|---|---|
mass_flow | Mass Flow Rate (m)(kg/s) | 5 |
cp | Specific Heat (Cp)(kJ/(kg·K)) | 4.18 |
temp_in | Inlet Temperature(°C) | 80 |
temp_out | Outlet Temperature(°C) | 40 |
How It Works
Heat Exchanger Duty
The thermal duty Q is the rate of heat transfer between the hot and cold streams. It is calculated from the energy balance on one side of the exchanger.
Formula
Q = m × Cp × |T_in - T_out|
where m is the mass flow rate, Cp is the specific heat capacity, and the temperature difference is the change experienced by the fluid. At steady state, the duty calculated on the hot side must equal the cold side (energy balance).
Worked Example
Water flowing at 5 kg/s is cooled from 80°C to 40°C.
mass_flow = 5cp = 4.18temp_in = 80temp_out = 40
- 01delta_T = |80 - 40| = 40°C
- 02Q = 5 × 4.18 × 40 = 836 kW
- 03In BTU/h: 836 × 3412.14 = 2,852,549 BTU/h
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