Overall Heat Transfer Calculator
Calculate the overall heat transfer coefficient U from heat duty, exchanger area, and LMTD.
Overall Heat Transfer Coefficient (U)
500.0 W/(m²·K)
Overall Heat Transfer Coefficient (U) vs Heat Duty (Q)
Formula
## 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.
Exemplo Resolvido
A heat exchanger transfers 500 kW with 20 m² area and 50°C LMTD.
- 01U = 500 × 1000 / (20 × 50)
- 02U = 500000 / 1000 = 500 W/(m²·K)
- 03In imperial: 500 × 0.176 = 88.1 BTU/(h·ft²·°F)
Perguntas Frequentes
What affects the overall heat transfer coefficient?
U depends on fluid velocities (higher velocity = better convection), fluid properties (viscosity, conductivity), tube material and thickness, and fouling deposits. Fouling always reduces U over time.
How is U used in exchanger sizing?
For a new design, estimate U from correlations or similar services, determine Q and LMTD from process requirements, then find required area A = Q / (U × LMTD). Add a fouling safety margin.
What is the fouling factor?
Fouling factor Rf adds thermal resistance: 1/U_dirty = 1/U_clean + Rf. Typical values: clean water 0.0001-0.0003 m²K/W, river water 0.0003-0.001, heavy fuel oil 0.001-0.003. TEMA standards provide recommended values.
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