Heat Transfer Calculation In Heat Exchanger

LMTD Method Formula:

\[ Q = U \times A \times \Delta T_{lm} \]

Overall Heat Transfer Coefficient (U):

W/m²K

Heat Transfer Area (A):

m²

Log Mean Temperature Difference (ΔT_lm):

Heat Transfer Rate (Q):

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1. What Is The LMTD Method?

The Log Mean Temperature Difference (LMTD) method is used to determine the temperature driving force for heat transfer in heat exchangers. It accounts for the logarithmic average of the temperature difference between the hot and cold fluids at each end of the heat exchanger.

2. How Does The Calculator Work?

The calculator uses the LMTD formula:

\[ Q = U \times A \times \Delta T_{lm} \]

Where:

\( Q \) — Heat transfer rate (W)
\( U \) — Overall heat transfer coefficient (W/m²K)
\( A \) — Heat transfer area (m²)
\( \Delta T_{lm} \) — Log mean temperature difference (K)

Explanation: The LMTD method provides an effective temperature difference for heat exchangers where temperatures change along the length of the exchanger.

3. Importance Of Heat Transfer Calculation

Details: Accurate heat transfer calculations are essential for designing efficient heat exchangers, optimizing energy usage, and ensuring proper sizing of heat transfer equipment in various industrial applications.

4. Using The Calculator

Tips: Enter the overall heat transfer coefficient in W/m²K, heat transfer area in m², and log mean temperature difference in K. All values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What Is The Difference Between LMTD And NTU Methods?
A: LMTD method is used when inlet and outlet temperatures are known, while NTU method is used when heat transfer area and overall coefficient are known but temperatures are unknown.

Q2: When Is LMTD Method Most Accurate?
A: LMTD method is most accurate for heat exchangers with constant overall heat transfer coefficient and when fluid properties don't vary significantly with temperature.

Q3: How Is Log Mean Temperature Difference Calculated?
A: For counter-flow heat exchangers: \( \Delta T_{lm} = \frac{(T_{h,in} - T_{c,out}) - (T_{h,out} - T_{c,in})}{\ln\left(\frac{T_{h,in} - T_{c,out}}{T_{h,out} - T_{c,in}}\right)} \)

Q4: What Are Typical Values For Overall Heat Transfer Coefficient?
A: Values range from 10-50 W/m²K for gas-gas systems, 100-1000 W/m²K for liquid-liquid systems, and up to 5000 W/m²K for condensation/vaporization systems.

Q5: What Are Common Applications Of This Calculation?
A: Used in design of shell and tube heat exchangers, plate heat exchangers, radiators, condensers, evaporators, and other thermal management systems.