Heat Exchanger Calculation Example

Heat Transfer Equation:

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

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 Heat Exchanger Calculation?

The heat exchanger calculation using the LMTD (Log Mean Temperature Difference) method determines the heat transfer rate between two fluids in a heat exchanger. This fundamental equation is essential for designing and analyzing heat exchange systems in various industrial applications.

2. How Does the Calculator Work?

The calculator uses the basic heat transfer equation:

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

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 equation calculates the rate of heat transfer based on the temperature driving force (ΔT_lm), the heat transfer surface area, and the overall heat transfer coefficient that accounts for all thermal resistances.

3. Importance of Heat Transfer Calculation

Details: Accurate heat transfer calculations are crucial for designing efficient heat exchangers, optimizing energy usage, sizing equipment properly, and ensuring process safety in chemical plants, power generation, HVAC systems, and manufacturing processes.

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 for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range for U values?
A: U values vary widely: 10-50 W/m²K for gas-gas, 100-500 W/m²K for liquid-liquid, and 1000-5000 W/m²K for condensation/evaporation systems.

Q2: How is ΔT_lm calculated?
A: For counter-current flow: ΔT_lm = (ΔT1 - ΔT2) / ln(ΔT1/ΔT2), where ΔT1 and ΔT2 are temperature differences at each end.

Q3: When is LMTD method applicable?
A: LMTD method works well for heat exchangers with constant U and when fluid temperatures change linearly with heat transfer.

Q4: What are limitations of this method?
A: Less accurate for complex flow arrangements, phase change processes, or when U varies significantly with temperature.

Q5: How to improve heat transfer rate?
A: Increase surface area, enhance turbulence, use higher conductivity materials, or optimize temperature differences.