Heat Exchanger Heat Transfer Calculation

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 Heat Exchanger Heat Transfer Calculation?

The heat exchanger heat transfer calculation determines the rate of heat transfer in heat exchangers using the Log Mean Temperature Difference (LMTD) method. This fundamental equation is essential for designing and analyzing heat exchanger performance in various industrial applications.

2. How Does the Calculator Work?

The calculator uses the LMTD 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 total heat transfer rate based on the overall heat transfer coefficient, available surface area, and the logarithmic mean temperature difference between the hot and cold fluids.

3. Importance of Heat Transfer Calculation

Details: Accurate heat transfer calculations are crucial for designing efficient heat exchangers, optimizing energy usage, ensuring proper sizing of equipment, and maintaining process temperature requirements in chemical, power, and HVAC systems.

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 log mean temperature difference (LMTD)?
A: LMTD is the logarithmic average of the temperature difference between the hot and cold fluids at each end of the heat exchanger, accounting for the changing temperature difference along the length.

Q2: How do I determine the overall heat transfer coefficient?
A: The overall heat transfer coefficient depends on the materials, fluid properties, flow arrangement, and fouling factors. It's typically determined experimentally or from empirical correlations.

Q3: What are typical values for overall heat transfer coefficient?
A: Values range from 10-50 W/m²K for gas-gas heat exchangers to 100-1000 W/m²K for liquid-liquid exchangers, and up to 5000 W/m²K for condensing vapors.

Q4: When is the LMTD method not applicable?
A: LMTD method is primarily for steady-state conditions with constant fluid properties and may not be accurate for complex flow arrangements or when there are phase changes.

Q5: How does heat exchanger type affect the calculation?
A: Different heat exchanger types (shell-and-tube, plate, cross-flow) require different correction factors for the LMTD calculation to account for their specific flow patterns.