LMTD Heat Exchanger Calculator
Calculate heat exchanger duty using Log Mean Temperature Difference (LMTD).
Find heat transfer rate, LMTD, required area, and correction factor for shell-and-tube and counterflow heat exchangers.
Log Mean Temperature Difference (LMTD) LMTD is the effective driving temperature difference for heat transfer in heat exchangers. Q = U × A × LMTD Where: Q = heat duty (W or kW) U = overall heat transfer coefficient (W/m²K) A = heat transfer area (m²) LMTD = log mean temperature difference (K or °C)
LMTD Formula LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁ / ΔT₂) Where ΔT₁ and ΔT₂ are the temperature differences at each end of the exchanger.
Counterflow vs Parallel Flow Counterflow: hot and cold streams flow in opposite directions. ΔT₁ = T_hot,in − T_cold,out | ΔT₂ = T_hot,out − T_cold,in Best LMTD — most efficient configuration. Parallel flow: both streams flow in the same direction. ΔT₁ = T_hot,in − T_cold,in | ΔT₂ = T_hot,out − T_cold,out Less efficient — temperature cross not possible.
LMTD Correction Factor F For multi-pass shell-and-tube exchangers, apply correction factor F: Q = U × A × F × LMTD_counterflow F depends on temperature efficiency and number of passes (charts in TEMA/HEDH). F = 1 for pure counterflow. Typically F = 0.8–1.0 for 2-pass shell-and-tube.
Overall Heat Transfer Coefficient U Typical U values (W/m²K): Water-water: 1,000–2,500 | Gas-gas: 10–50 | Steam-water: 1,000–3,500 Oil-water: 300–900 | Condensing steam: 1,500–8,000 Gas-liquid: 20–200
Energy Balance Hot side: Q = ṁ_h × Cp_h × (T_h,in − T_h,out) Cold side: Q = ṁ_c × Cp_c × (T_c,out − T_c,in)