Heat Exchanger Calculator Formula
Understand the math behind the heat exchanger calculator. Each variable explained with a worked example.
Formulas Used
Temperature Difference
delta_t = abs(temp_in - temp_out)Heat Transfer Rate
heat_rate = flow_rate * specific_heat * abs(temp_in - temp_out)Variables
| Variable | Description | Default |
|---|---|---|
flow_rate | Mass Flow Rate(kg/s) | 2 |
specific_heat | Specific Heat (cp)(kJ/(kg-K)) | 4.18 |
temp_in | Inlet Temperature(deg C) | 80 |
temp_out | Outlet Temperature(deg C) | 50 |
How It Works
Heat Exchanger Energy Balance
The heat transfer rate is determined by the fluid properties and temperature change.
Formula
Q = m_dot cp delta_T
where m_dot is the mass flow rate, cp is the specific heat capacity, and delta_T is the temperature change of the fluid. This applies to each fluid stream independently; at steady state, the heat lost by the hot stream equals the heat gained by the cold stream (minus losses).
Worked Example
Water at 2 kg/s cooled from 80 deg C to 50 deg C.
- 01delta_T = 80 - 50 = 30 deg C
- 02Q = 2 x 4.18 x 30 = 250.8 kW
- 03This is the heat that must be transferred to the cooling medium.
Frequently Asked Questions
What types of heat exchangers exist?
Shell-and-tube (most common in industry), plate-and-frame (compact, high efficiency), finned-tube (air-cooled), double-pipe (simple, small duties), and spiral (fouling resistance). Selection depends on duty, pressures, and fouling.
What is LMTD?
Log Mean Temperature Difference is the effective driving force for heat transfer: LMTD = (delta_T1 - delta_T2) / ln(delta_T1 / delta_T2). It is used to size the heat exchanger area: Q = U A LMTD, where U is the overall heat transfer coefficient.
What is specific heat for common fluids?
Water: 4.18 kJ/(kg-K). Air: 1.005. Ethylene glycol (50%): 3.35. Thermal oil: 1.7-2.3. Steam: 2.01 (at 100 deg C, 1 atm). Refrigerant R134a liquid: 1.43.
Ready to run the numbers?
Open Heat Exchanger Calculator