Heat Exchanger Calculator | LMTD, Heat Transfer, Area

📖 How to Use This Heat Exchanger Calculator

Enter hot fluid temperatures – Inlet and outlet temperatures of the hot fluid in °C.

Enter cold fluid temperatures – Inlet and outlet temperatures of the cold fluid in °C.

Select flow configuration – Choose between counter flow or parallel flow arrangement.

Enter heat transfer rate (Q) – The amount of heat being transferred in kW.

Enter overall heat transfer coefficient (U) – Typical values: 200-800 W/m²·K for liquid-liquid, 10-50 for gas-gas.

🔥 Understanding Heat Exchanger Design

The Log Mean Temperature Difference (LMTD) is the driving force for heat transfer in heat exchangers. It accounts for the temperature change of both fluids along the heat exchanger length.

The key formulas are:

For Counter Flow:
ΔT₁ = T_h,in - T_c,out | ΔT₂ = T_h,out - T_c,in
For Parallel Flow:
ΔT₁ = T_h,in - T_c,in | ΔT₂ = T_h,out - T_c,out
LMTD = (ΔT₁ - ΔT₂) / ln(ΔT₁/ΔT₂)
Required Area: A = Q / (U × LMTD)

💡 Practical Applications

Power plants – Condensers, boilers, and cooling systems.
HVAC systems – Chillers, cooling coils, and heat recovery.
Chemical processing – Reactor cooling, distillation, and evaporation.
Food processing – Pasteurization, sterilization, and cooling.
Oil & gas – Heat exchangers for refining and processing.

❓ Frequently Asked Questions (FAQ)

What is LMTD and why is it important?

LMTD (Log Mean Temperature Difference) is the average temperature difference between the hot and cold fluids over the length of the heat exchanger. It's the driving force for heat transfer and determines the required surface area.

What is the difference between counter flow and parallel flow?

In counter flow, the fluids move in opposite directions, providing a more uniform temperature difference and higher LMTD. In parallel flow, both fluids move in the same direction, which results in a lower LMTD. Counter flow is generally more efficient.

What is the overall heat transfer coefficient (U)?

U is the overall heat transfer coefficient that accounts for all thermal resistances (convection, conduction, fouling). Typical values: 200-800 W/m²·K for liquid-liquid, 10-50 for gas-gas, 500-2000 for condensing.

What is temperature cross?

Temperature cross occurs when the cold fluid outlet temperature exceeds the hot fluid outlet temperature in a counter flow heat exchanger. This indicates efficient heat transfer and is only possible in counter flow arrangements.

What is the effectiveness of a heat exchanger?

Effectiveness is the ratio of actual heat transfer to the maximum possible heat transfer. The NTU method is often used for heat exchanger analysis, especially when outlet temperatures are unknown.

What is a reasonable value for U?

Water-water: 500-1000 W/m²·K. Oil-water: 200-500 W/m²·K. Gas-gas: 10-50 W/m²·K. Condensing: 500-2000 W/m²·K. Always consult design references for specific applications.