Heat Exchanger Design Calculator

Calculator Inputs

Enter thermal data, select the flow arrangement, and choose either a direct overall coefficient or a resistance-based estimate.

Flow arrangement

Overall coefficient mode

LMTD correction factor F

Hot inlet temperature (°C)

Hot outlet temperature (°C)

Cold inlet temperature (°C)

Cold outlet temperature (°C)

Hot mass flow rate (kg/s)

Cold mass flow rate (kg/s)

Hot specific heat (kJ/kg·K)

Cold specific heat (kJ/kg·K)

Direct overall U (W/m²·K)

Hot-side film coefficient h_hot (W/m²·K)

Cold-side film coefficient h_cold (W/m²·K)

Hot fouling resistance (m²·K/W)

Cold fouling resistance (m²·K/W)

Wall thickness (mm)

Wall conductivity (W/m·K)

Oversize allowance (%)

Available or check area (m²)

Tube outer diameter (mm)

Tube length per tube (m)

Shell passes

Tube passes

Plotly Temperature Profile

The graph compares hot-side and cold-side temperature paths across the exchanger length scale.

Formula Used

Q_hot = m_hot × Cp_hot × (T_hot,in − T_hot,out)

Q_cold = m_cold × Cp_cold × (T_cold,out − T_cold,in)

ΔT_lm = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2)

Q = U × A × F × ΔT_lm

A_required = Q / (U × F × ΔT_lm)

1 / U = (1 / h_hot) + R_f,hot + (t / k_wall) + R_f,cold + (1 / h_cold)

C = m × Cp, C_r = C_min / C_max, NTU = UAF / C_min

ε_parallel = [1 − exp(−NTU(1 + C_r))] / (1 + C_r)

ε_counter = [1 − exp(−NTU(1 − C_r))] / [1 − C_r exp(−NTU(1 − C_r))]

This page uses entered temperatures for duty and LMTD sizing, and uses the selected or calculated overall coefficient for area and NTU checks.

How to Use This Calculator

Choose counterflow or parallel flow.
Enter inlet and outlet temperatures for both streams.
Enter mass flow rates and specific heats.
Select either direct U input or resistance-based U estimation.
Set the LMTD correction factor and oversize allowance.
Enter available area if you want an NTU performance check.
Add tube diameter and tube length to estimate tube count.
Click Calculate Design to view results, chart, and export buttons.

Example Data Table

Parameter	Example Value	Unit
Flow arrangement	Counterflow	—
Hot inlet temperature	180	°C
Hot outlet temperature	120	°C
Cold inlet temperature	30	°C
Cold outlet temperature	85	°C
Hot mass flow rate	2.50	kg/s
Cold mass flow rate	3.20	kg/s
Hot specific heat	2.20	kJ/kg·K
Cold specific heat	4.18	kJ/kg·K
Overall U	650	W/m²·K
Correction factor	0.95	—
Tube outer diameter	25.4	mm
Tube length	6	m

Frequently Asked Questions

1) What does this calculator estimate?

It estimates heat duty, LMTD, required heat-transfer area, NTU, effectiveness, and an approximate tube count from the process conditions you enter.

2) When should I choose counterflow?

Choose counterflow when you want stronger thermal driving force and often lower required area for the same duty. It is commonly preferred for efficient recovery.

3) What is the correction factor F for?

F adjusts ideal LMTD sizing when the exchanger arrangement is not a simple single-pass pure counterflow unit. Lower values reduce effective thermal driving force.

4) Why do hot-side and cold-side duties differ sometimes?

Differences usually come from inconsistent temperatures, estimated properties, rounding, or process data collected from different operating points. The calculator flags large imbalance values.

5) Should I use direct U or resistance mode?

Use direct U when you already have a design coefficient from experience, standards, or prior calculations. Use resistance mode when you want a transparent estimate from film, wall, and fouling terms.

6) Does tube count here replace mechanical design?

No. It is a quick preliminary estimate from outside area only. Detailed shell, baffle, vibration, pressure-drop, and code checks still need separate engineering work.

7) Can I use this for phase-change services?

Not directly. Condensers, reboilers, and boiling duties usually need phase-change property methods, special coefficients, and service-specific correction procedures.

8) What should I do if the LMTD fails?

Check terminal temperatures first. A failed LMTD usually means the selected stream temperatures are physically impossible for the chosen flow arrangement or were entered incorrectly.