Thermal EngineeringP0

Heat Exchanger Calculator (LMTD Method)

Calculate heat transfer rate using the LMTD (Log Mean Temperature Difference) method: Q = U × A × LMTD.

Inputs

Enter your values below

Heat Transfer Coefficient (U)*W/(m²·K)

Heat Transfer Area*m2

Hot Fluid Inlet Temperature*C

Hot Fluid Outlet Temperature*C

Cold Fluid Inlet Temperature*C

Cold Fluid Outlet Temperature*C

Result

Heat Transfer Rate

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Enter values and click Calculate

Formula

u  ×  area  ×  ((t1_hot  −  t2_cold)  −  (t2_hot  −  t1_cold))  ÷  log((t1_hot  −  t2_cold)  ÷  (t2_hot  −  t1_cold))  ÷  1000

Result unit: kW

Q = U × A × LMTD where LMTD = (ΔT1 − ΔT2) / ln(ΔT1/ΔT2). Counter-current flow assumed. ΔT1 = T_hot_in − T_cold_out, ΔT2 = T_hot_out − T_cold_in.

Introduction

Calculate heat transfer rate for a heat exchanger using the Log Mean Temperature Difference (LMTD) method. This calculator assumes counter-current flow and uses the standard Q = U·A·LMTD formula.

Calculation Example

50m² exchanger, U=500 W/m²K, ΔT1=50°C (hot in−cold out), ΔT2=40°C (hot out−cold in), LMTD=44.8 → Q ≈ 1120 kW

Inputs: u=500, area=50, t1_hot=100, t2_hot=60, t1_cold=20, t2_cold=50

Result: 1120 kW

Engineering Applications

•Heat exchanger sizing
•Process thermal design
•HVAC design
•Energy recovery

Frequently Asked Questions

What is LMTD?

Log Mean Temperature Difference accounts for the varying temperature driving force along the heat exchanger. It is the logarithmic average of the temperature differences at each end.

What is a typical U value?

For liquid-liquid exchangers: 300-1000 W/m²K. For gas-liquid: 50-300 W/m²K. For condensing/boiling: 1000-5000 W/m²K.

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Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.