What does this tool calculate?

This tool calculates heat transfer rate Q, effectiveness ε, NTU (Number of Transfer Units), hot and cold fluid outlet temperatures, LMTD (Log Mean Temperature Difference), and required heat transfer area A_req in real time. It supports parallel-flow, counter-flow, and crossflow configurations.

How do I use this calculator?

Select the flow configuration (parallel, counter, or crossflow) in the left panel, then set the inlet temperatures, flow rates, and specific heats for both the hot and cold fluids. Adjust the overall heat transfer coefficient U (W/m²K) and heat transfer area A (m²) with the sliders. Results and the ε-NTU family curves appear instantly on the right.

What is the difference between the NTU-effectiveness method and the LMTD method?

The NTU-effectiveness (ε-NTU) method uses NTU = UA/C_min and is most powerful when outlet temperatures are unknown (design problems). The LMTD method is ideal for rating problems where outlet temperatures are known and you need to back-calculate the required area. Both describe the same physics; the choice depends on what is given and what is sought.

Why does counter-flow give the highest effectiveness?

In counter-flow, hot and cold fluids travel in opposite directions, maintaining a large temperature difference ΔT along the entire length of the exchanger. The ε-NTU relation for counter-flow therefore yields the highest effectiveness for any given NTU, and temperature crossover is theoretically possible. Parallel-flow is limited because ΔT approaches zero at the outlet end.

/ Heat Exchanger Design Calculator Tools Index

JP | EN | ZH

Thermal Analysis Tool

Heat Exchanger Design Calculator
NTU-Effectiveness / LMTD Method

Real-time design of parallel, counter, and crossflow heat exchangers using the NTU-effectiveness method. Visualize ε–NTU family curves and axial temperature profiles.

$$\varepsilon = \frac{Q}{Q_{\max}} = \frac{Q}{C_{\min}(T_{h,\text{in}} - T_{c,\text{in}})}$$

Parameters

Flow Arrangement

Parallel Counter Crossflow

Hot Fluid

T_h_in 120 °C

m_h 2.0 kg/s

Cp_h 4182 J/kg·K

Cold Fluid

T_c_in 20 °C

m_c 1.5 kg/s

Cp_c 4182 J/kg·K

Overall Heat Transfer Coeff. U 1000 W/m²K

Liquid–liquid ≈ 1000, Gas–gas ≈ 50

Transfer Area A 10.0 m²

Heat Transfer Q

—

Effectiveness ε

—

NTU

—

dimensionless

T_h_out

—

°C

T_c_out

—

°C

LMTD

—

Required Area A_req

—

m²

ε–NTU Family Curves

Temperature Profile (x/L)

Theory — NTU-Effectiveness / LMTD Method

Effectiveness Definition

$$\varepsilon = \frac{Q}{Q_{\max}},\quad Q_{\max} = C_{\min}(T_{h,\text{in}} - T_{c,\text{in}})$$

Counter-flow ε–NTU Equation

$$\varepsilon = \frac{1 - e^{-\text{NTU}(1-C_r)}}{1 - C_r e^{-\text{NTU}(1-C_r)}}$$

$C_r = C_{\min}/C_{\max}$

NTU and Transfer Area

$$\text{NTU} = \frac{UA}{C_{\min}}$$

U: overall heat transfer coefficient, A: transfer area

LMTD (Log Mean Temperature Difference)

$$\text{LMTD} = \frac{\Delta T_1 - \Delta T_2}{\ln(\Delta T_1/\Delta T_2)}$$

Counter-flow: ΔT₁=T_h,in−T_c,out, ΔT₂=T_h,out−T_c,in

Heat Exchanger Design CalculatorNTU-Effectiveness / LMTD Method

Effectiveness Definition

Counter-flow ε–NTU Equation

NTU and Transfer Area

LMTD (Log Mean Temperature Difference)

Heat Exchanger Design Calculator
NTU-Effectiveness / LMTD Method