LMTD Calculator: worked example
This example is generated from PROFENG's own default input set and the implemented relationship. It is not copied from a cited publication.
Relationship
LMTD = (ΔT₁−ΔT₂)/ln(ΔT₁/ΔT₂)
This calculator determines lmtd from terminal temperature difference 1, terminal temperature difference 2. Use it to screen energy, temperature and heat-transfer relationships with explicitly stated properties and boundary conditions.
Inputs
- Terminal temperature difference 1 (dt1) = 50 K
- Terminal temperature difference 2 (dt2) = 20 K
Working
Math.abs((50)-(20))<1e-9?(50):((50)-(20))/Math.log((50)/(20)) = 32.741 K
LMTD: 32.741 K
Assumptions and limits
- Properties entered by the user are treated as constant over the calculation unless the formula explicitly varies them.
- Temperatures and temperature differences must use the unit convention shown by the calculator.
- The model is lumped or one-dimensional where implied by the displayed relationship.
- Terminal temperature differences must be positive and correspond to one heat-exchanger flow arrangement.
- The LMTD method assumes a steady exchanger and is normally combined with an appropriate overall heat-transfer coefficient and correction factor where required.
Formula source and acknowledgement
Theodore L. Bergman, Adrienne S. Lavine, Frank P. Incropera, David P. DeWitt, Fundamentals of Heat and Mass Transfer, 8th, 2018, Wiley. Credit belongs to the cited author(s)/publisher; PROFENG presents its own implementation and does not imply endorsement.
Automated verification passed – 30 September 2026 – six numerical cases checked, with dimensional checks and an independent implementation where applicable.
This worked example is for engineering screening and education. Replace defaults with traceable project data and confirm the method, assumptions, standards and equipment information before design, procurement or operation.