Heat Exchanger Calculator (LMTD & NTU Methods)
Calculate heat transfer area, effectiveness, and duty for parallel, counterflow, and cross-flow configurations.
Results (LMTD Method)
Results (NTU Method)
About Heat Exchanger Calculations
The Logarithmic Mean Temperature Difference (LMTD) method and the Effectiveness-NTU method are two complementary approaches for heat exchanger analysis.
LMTD Method Formula:
ΔTlm = (ΔT1 – ΔT2) / ln(ΔT1/ΔT2)
Where ΔT1 and ΔT2 are the temperature differences at each end of the heat exchanger.
NTU Method Formula:
ε = (1 – exp[-NTU(1 + Cr)]) / (1 + Cr) for counter flow
Where ε is effectiveness, NTU is number of transfer units, and Cr is capacity ratio.
This calculator supports parallel flow, counter flow, and cross flow configurations with automatic correction factors.
Understanding LMTD and NTU in Heat Exchangers
Heat exchangers play a vital role in many engineering systems by allowing heat transfer between two fluids. Two commonly used methods to analyze this process are LMTD (Log Mean Temperature Difference) and NTU (Number of Transfer Units). These approaches help determine how effectively a heat exchanger operates, depending on what data is available.
What is LMTD?
LMTD helps calculate the average temperature difference between hot and cold fluids flowing through a heat exchanger. This temperature difference is the main factor that drives heat transfer. This method works well when both inlet and outlet temperatures are known and the system is in steady-state.
Use this formula:
Q = U × A × LMTDWhere:
- Q = heat transferred
- U = overall heat transfer coefficient
- A = surface area
- LMTD = log mean temperature difference
The temperature differences vary based on the flow arrangement:
- Parallel Flow: ΔT₁ = Thot,in – Tcold,in, ΔT₂ = Thot,out – Tcold,out
- Counter Flow: ΔT₁ = Thot,in – Tcold,out, ΔT₂ = Thot,out – Tcold,in
Then apply:
LMTD = (ΔT₁ – ΔT₂) / ln(ΔT₁ / ΔT₂)For steady-state conduction scenarios, try our
👉 Conduction Heat Transfer Calculator (Plane Wall) or
👉 Conduction in Cylindrical/Spherical Coordinates
What is NTU?
The NTU method is ideal when outlet temperatures are unknown. It helps in designing heat exchangers from scratch or analyzing performance when some data is missing.
NTU is calculated using:
NTU = (U × A) / C<sub>min</sub>Where:
- U = heat transfer coefficient
- A = area
- Cmin = minimum heat capacity rate of the two fluids
This method works along with effectiveness (ε), which tells how efficiently the heat exchanger operates:
ε = q / q<sub>max</sub>q<sub>max</sub> = C<sub>min</sub> × (T<sub>hot,in</sub> – T<sub>cold,in</sub>)For complete cycle analysis, explore our
👉 Thermodynamic Cycle Analyzer
Key Differences: LMTD vs NTU
| Feature | LMTD Method | NTU Method |
|---|---|---|
| Input Requirements | Needs both inlet and outlet temperatures | Works even if outlet temperatures are unknown |
| Use Case | Analysis of existing systems | Ideal for designing new systems |
| Flexibility | Limited to standard configurations | Supports complex designs and configurations |
| Design Capability | Not suitable | Suitable for design tasks |
Practical Applications and Tools
- If you’re analyzing fuel or combustion processes in heat exchange systems, check out the
👉 Combustion/Fuel Calculator - For radiative heat transfer between surfaces:
👉 Radiation Heat Transfer Calculator - For systems with extended surfaces (fins):
👉 Extended Surface (Fins) Calculator - To evaluate convective heat transfer and Nusselt numbers:
👉 Convection/Nusselt Number Calculator - Working with steam, refrigerants, or gases? Try these:
Both LMTD and NTU methods serve different purposes. LMTD is great when complete temperature data is available, while NTU is the go-to method for design and complex systems. Using tools like the ones above can make your thermodynamic calculations easier, faster, and more accurate.