Overall Heat Transfer Calculator Formula
Understand the math behind the overall heat transfer calculator. Each variable explained with a worked example.
Formulas Used
Overall Heat Transfer Coefficient (U)
u_coeff = duty * 1000 / (area * lmtd)U (Imperial)
u_btu = duty * 1000 / (area * lmtd) * 0.17611Variables
| Variable | Description | Default |
|---|---|---|
duty | Heat Duty (Q)(kW) | 500 |
area | Heat Transfer Area (A)(m²) | 20 |
lmtd | LMTD(°C) | 50 |
How It Works
Overall Heat Transfer Coefficient
The overall heat transfer coefficient U combines all thermal resistances (convection on both sides, wall conduction, fouling) into a single parameter for heat exchanger design.
Formula
Q = U × A × LMTD, therefore U = Q / (A × LMTD)
Typical U values: water-water: 800-1500 W/(m²·K), gas-gas: 10-40, condensing steam-water: 1000-4000. Low U indicates fouling or poor heat transfer conditions.
Worked Example
A heat exchanger transfers 500 kW with 20 m² area and 50°C LMTD.
duty = 500area = 20lmtd = 50
- 01U = 500 × 1000 / (20 × 50)
- 02U = 500000 / 1000 = 500 W/(m²·K)
- 03In imperial: 500 × 0.176 = 88.1 BTU/(h·ft²·°F)
Ready to run the numbers?
Open Overall Heat Transfer Calculator