Calculator Inputs
Use the responsive grid below: three columns on large screens, two on smaller, and one on mobile.
Example Data Table
These examples illustrate typical inputs and outputs. Use them to validate your own scenarios quickly.
| Case | Th,in → Th,out (°C) | Tc,in → Tc,out (°C) | ṁh, cₚh | ṁc, cₚc | U (W/m²·K) | F | Arrangement | Key Output |
|---|---|---|---|---|---|---|---|---|
| A | 160 → 120 | 30 → 70 | 1.2 kg/s, 4.2 | 1.5 kg/s, 4.0 | 650 | 0.92 | Counter | Sizes area using LMTD + F |
| B | 95 → 70 | 25 → 45 | 0.9 kg/s, 3.9 | 1.0 kg/s, 4.0 | 500 | 1.00 | Parallel | Compare LMTD sensitivity |
| C | 210 → 150 | 60 → 120 | 2.0 kg/s, 2.3 | 1.8 kg/s, 4.1 | 800 | 0.85 | Counter | Higher duty, larger area |
Download the example CSV for a ready-to-import dataset.
Formulas Used
Energy Balance
Heat duty is estimated from each side (kW):
Q = ṁ · cₚ · (T_in − T_out) (hot)
Q = ṁ · cₚ · (T_out − T_in) (cold)
The calculator can use the smaller, average, or a selected side.
Q = ṁ · cₚ · (T_in − T_out) (hot)
Q = ṁ · cₚ · (T_out − T_in) (cold)
The calculator can use the smaller, average, or a selected side.
LMTD Method
Temperature differences depend on flow arrangement.
LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁/ΔT₂)
Heat transfer rate:
Q = U · A · F · LMTD
LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁/ΔT₂)
Heat transfer rate:
Q = U · A · F · LMTD
1–2 Correction Factor (Optional)
For one shell pass and two tube passes, the correction factor is estimated from:
R = (Th,in − Th,out)/(Tc,out − Tc,in)
S = (Tc,out − Tc,in)/(Th,in − Tc,in)
A standard analytical expression is used; use manual F if inputs create singularities.
R = (Th,in − Th,out)/(Tc,out − Tc,in)
S = (Tc,out − Tc,in)/(Th,in − Tc,in)
A standard analytical expression is used; use manual F if inputs create singularities.
Overall U from Resistances (Optional)
Outer-area basis approximation:
1/Uₒ = 1/hₒ + Rᶠₒ + (dₒ/2k)ln(dₒ/dᵢ) + (dₒ/dᵢ)(Rᶠᵢ + 1/hᵢ)
Units: U (W/m²·K), diameters (m), k (W/m·K), fouling (m²·K/W).
1/Uₒ = 1/hₒ + Rᶠₒ + (dₒ/2k)ln(dₒ/dᵢ) + (dₒ/dᵢ)(Rᶠᵢ + 1/hᵢ)
Units: U (W/m²·K), diameters (m), k (W/m·K), fouling (m²·K/W).
Tube Surface Area
Outer tube area is computed as:
A = N · π · dₒ · L
In sizing mode, the calculator can estimate missing tube length or tube count if the other is provided.
A = N · π · dₒ · L
In sizing mode, the calculator can estimate missing tube length or tube count if the other is provided.
How to Use This Calculator
- Enter hot and cold inlet and outlet temperatures in °C.
- Add mass flow rates and heat capacities to compute the energy duty.
- Choose sizing to estimate required area, or rating to estimate duty.
- Enter U directly, or switch to resistance-based U for detail.
- Pick an F option; use auto-calc only when terminal temperatures are reliable.
- Optional: enter tube count, length, and outside diameter to compute actual area.
- Press Submit to view results above the form, then export CSV or PDF.
FAQs
1) What is LMTD and why is it used?
LMTD represents the effective driving temperature difference across the exchanger. It combines end-point differences into one value, improving accuracy compared with a simple average when temperature differences vary along the length.
2) When should I apply a correction factor F?
Use F when the exchanger deviates from pure counterflow or parallel flow, such as multi-pass tube arrangements. If you do not know the pass configuration, start with F = 1 and then refine with a documented assumption.
3) Why do hot-side and cold-side duties sometimes differ?
Real data can include sensor error, heat losses, phase change, or incorrect heat capacity values. The calculator flags mismatches and lets you pick a conservative duty choice to continue sizing.
4) Which units are assumed for flow rate and heat capacity?
Mass flow is in kg/s and heat capacity is in kJ/kg·K. With these units, Q is produced in kW. Temperatures are in °C and temperature differences are treated as K.
5) How is U computed from resistances?
The tool uses an outer-area basis resistance network including inside and outside film terms, fouling resistances, and tube wall conduction with a logarithmic diameter ratio. This provides a practical estimate for preliminary checks.
6) What does sizing mode output?
Sizing mode calculates required area from the selected duty, LMTD, U, and F. It also applies an oversize margin to report design area and can back-calculate tube length or tube count when geometry is provided.
7) What does rating mode output?
Rating mode calculates heat duty from U·A·F·LMTD using your provided exchanger area. If you also provide flows and heat capacities, it estimates outlet temperatures based on the computed duty.
8) When is the NTU method helpful?
NTU is useful when outlet temperatures are unknown but inlet temperatures and capacity rates are known, and you have an area estimate for UA. It provides effectiveness, NTU, and an alternate duty estimate for comparison.