Logarithmic Mean Temperature Difference Calculator

The Logarithmic Mean Temperature Difference (LMTD) is used in heat exchanger calculations to determine the temperature driving force for heat transfer. This calculator helps you calculate the LMTD between two fluids in a heat exchanger.

Input Parameters

Calculation Results

Calculation Formula

LMTD = (ΔT1 - ΔT2) / ln(ΔT1 / ΔT2)

Where:
ΔT1 = T1 - T4 (Hot inlet - Cold outlet)
ΔT2 = T2 - T3 (Hot outlet - Cold inlet)

Logarithmic Mean Temperature Difference Calculator Usage Guide

Learn how to use the LMTD calculator for heat exchanger design and analysis

What is LMTD?

The Logarithmic Mean Temperature Difference (LMTD) is a logarithmic average of the temperature differences between the hot and cold fluids in a heat exchanger. It is used to calculate the heat transfer in heat exchangers and is particularly useful for heat exchangers where the temperature of either fluid changes along the exchanger's length.

How to Use This Calculator

  1. Enter the inlet and outlet temperatures for both the hot and cold fluids in degrees Celsius.
  2. The hot fluid temperatures should be entered in the first two fields (T1 and T2), and the cold fluid temperatures in the last two fields (T3 and T4).
  3. Click the "Calculate" button to compute the LMTD.
  4. The result will be displayed in degrees Celsius.

Important Notes

  • The LMTD is used in the heat transfer equation Q = U × A × LMTD, where Q is the heat transfer rate, U is the overall heat transfer coefficient, and A is the heat transfer area.
  • If the calculated LMTD is infinite, it indicates that the temperature difference between the hot and cold fluids is constant throughout the heat exchanger (which is rare in practical applications).
  • The LMTD method is most accurate for heat exchangers with counter-current flow. For other flow arrangements (parallel flow, cross flow), correction factors may be needed.

Principle Explanation

The LMTD formula accounts for the changing temperature differences along the length of a heat exchanger. Instead of using the arithmetic mean of the temperature differences, the logarithmic mean provides a more accurate representation of the average temperature driving force for heat transfer.