Heat Exchanger Calculator (LMTD & NTU)
LMTD, one-shell correction, effectiveness-NTU, heat balance and required exchanger area.
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- Free preview: the rules, dates and checks that apply to your figures, with every computed amount hidden.
- Locked until you unlock it: download and copy.
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Working
Assumptions and sources
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Results are estimates from the formulas shown, not a professional design or certification. Have a qualified engineer verify anything safety-critical (structures, electrical installations, gas or pressure systems).
About the Heat Exchanger Calculator (LMTD & NTU)
Rate a heat exchanger from measured inlet and outlet temperatures using LMTD, predict outlet temperatures from a known UA, or find the area needed for an attainable heat duty. Counter-flow, parallel-flow and one-shell/two-tube-pass arrangements are supported; NTU modes also include common mixed and unmixed cross-flow configurations. The free preview hides computed figures and retains the applicable warnings; a Pro pass opens the full result and exports.
How to use it
- Choose measured-temperature LMTD, known-UA rating or target-duty sizing, then choose the flow configuration.
- Enter hot and cold inlet temperatures, mass flows and specific heats in the stated SI units.
- For LMTD, enter both measured outlets; for rating, enter UA; for sizing, enter target duty. Enter U to obtain area.
- Check heat-balance mismatch and model assumptions before using the estimate; unattainable duties and invalid terminal differences are rejected.
- Use the free preview, then unlock with a Pro pass to copy the result or download CSV, PDF and the effectiveness chart.
Examples
1 kg/s on each side, cp=4.18 kJ/kg/K, inlets 100 and 20 degC, UA=4180 W/K
NTU=1, effectiveness=0.5, duty=167.2 kW, both outlets 60 degC. At U=500 W/m2/K the area is 8.36 m2.
Equations and assumptions
Stream capacity C = mass flow × cp. Qmax = Cmin(Th,in − Tc,in); NTU = UA/Cmin and Q = εQmax. Counter-flow ε = [1 − exp(−NTU(1−Cr))]/[1 − Cr exp(−NTU(1−Cr))], with NTU/(1+NTU) at Cr=1. LMTD = (ΔT1−ΔT2)/ln(ΔT1/ΔT2), using the common value when both differences are equal; Q = UFALMTD. One-shell/two-pass F uses the standard shell correction relation. Both-streams-unmixed cross-flow uses the conventional approximate effectiveness correlation.
Sources
Limitations
- Estimate — not a professional design. Constant properties, negligible external heat loss, no phase change and the stated ideal flow arrangement are assumed.
- LMTD cross-flow correction factors are not guessed; use the supported NTU configuration for cross-flow.
- An unbalanced measured heat duty is flagged. The calculated LMTD area uses the measured hot-side duty and is not a validated balanced design.
- A target near an arrangement’s ideal effectiveness limit makes required area very sensitive to temperatures and properties. A numerical result does not establish practical equipment feasibility.
- Fouling, pressure drop, mechanical design, vibration and exchanger selection are outside this calculation.
- PDF needs the PDF engine and any required fonts cached for offline use; inputs never leave the device.
Privacy
On this device; its files download once
All entered dimensions, temperatures, labels and schedules stay on your device. PDF fonts and calculation code can download from MySmartCoPilot; inputs are never sent with those downloads.
Frequently asked questions
What do I get without a pass?
Without a pass, Heat Exchanger Calculator (LMTD & NTU) shows the rules, dates and checks that apply to your figures, with every computed amount hidden. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
When should I use LMTD rather than NTU?
Use LMTD when terminal temperatures are known; use NTU when inlet conditions and UA are known. Target-duty sizing inverts the supported effectiveness relation.
Why can a target below Qmax still be impossible?
Some arrangements have an effectiveness limit below one for a given capacity ratio. Increasing area cannot exceed that configuration limit.
Why are hot and cold measured duties different?
Measured flows, temperatures or properties can be inconsistent, or heat can be lost outside the exchanger. The tool shows the mismatch instead of silently forcing the two measurements to agree.