Log Mean Temp Diff

Log Mean Temp Diff Equation:

\[ LMTD = \frac{\Delta T_1 - \Delta T_2}{\ln(\Delta T_1 / \Delta T_2)} \]

Log Mean Temp Diff (°C):

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1. What is Log Mean Temperature Difference?

The Log Mean Temperature Difference (LMTD) is used to determine the temperature driving force for heat transfer in heat exchangers. It provides an average temperature difference between the hot and cold fluids that accounts for the logarithmic relationship.

2. How Does the Calculator Work?

The calculator uses the LMTD equation:

\[ LMTD = \frac{\Delta T_1 - \Delta T_2}{\ln(\Delta T_1 / \Delta T_2)} \]

Where:

\( \Delta T_1 \) — Temperature difference at one end of the heat exchanger (°C)
\( \Delta T_2 \) — Temperature difference at the other end of the heat exchanger (°C)

Explanation: The LMTD method accounts for the varying temperature difference along the length of the heat exchanger, providing a more accurate average than a simple arithmetic mean.

3. Importance of LMTD Calculation

Details: Accurate LMTD calculation is crucial for designing and analyzing heat exchangers, determining heat transfer rates, and optimizing thermal system performance in various industrial applications.

4. Using the Calculator

Tips: Enter both temperature differences in °C. Both values must be positive and not equal to each other for the calculation to be valid.

5. Frequently Asked Questions (FAQ)

Q1: Why use LMTD instead of arithmetic mean?
A: LMTD provides a more accurate representation of the average temperature difference in heat exchangers where the temperature difference varies along the length.

Q2: What are typical LMTD values in heat exchangers?
A: Typical values range from 5-50°C depending on the application, with higher values indicating greater driving force for heat transfer.

Q3: When is LMTD method not applicable?
A: The LMTD method assumes constant overall heat transfer coefficient and may not be suitable for cases with phase change or variable properties.

Q4: Can LMTD be negative?
A: No, LMTD is always positive as it represents the magnitude of the temperature driving force for heat transfer.

Q5: How does flow arrangement affect LMTD?
A: Different flow arrangements (counterflow, parallel flow, crossflow) require different LMTD correction factors for accurate calculations.