Engineering calculator reviewed for preliminary design use · Last updated: March 2026
Calculate log mean temperature difference (LMTD) for heat exchanger design. Supports both counterflow and parallel flow configurations. Also computes the F-correction factor for shell-and-tube exchangers. Use as input to Q=UA×LMTD×F for area calculation.
Log Mean Temperature Difference (LMTD)
LMTD is the driving force for heat transfer in a heat exchanger. It represents the effective average temperature difference between the hot and cold streams and is more accurate than a simple arithmetic mean.
F: Correction factor for multi-pass or cross-flow (typically 0.7–0.95)
Design Tips
Counter-flow configurations achieve higher LMTD than parallel-flow, enabling more compact designs. For shell-and-tube exchangers, apply an F correction factor to account for cross-flow mixing.
F correction is needed for multi-pass shell-and-tube exchangers. For pure counterflow or pure parallel flow, F = 1. For 1-2 or 2-4 configurations, F < 1 and depends on the R and P ratios.
What if LMTD is very small or zero?
A very small LMTD means the temperature driving force is weak, requiring a very large heat transfer area. If LMTD approaches zero, the exchanger design is impractical. Consider changing flow arrangement or temperatures.
These results are preliminary estimates for screening-level design use. They do not replace detailed engineering, code compliance verification, or vendor-certified calculations.