Engineering
Heat Exchanger Preliminary Design Calculator
Calculate corrected LMTD, clean required area, design area with allowance, installed capacity, area margin, and an independent hot-stream sensible-duty check.
Corrected LMTD F times LMTD-
Clean area required by Q over U DeltaT-
Required area including fouling margin-
Installed area minus design requirement-
Design requirement divided by installed area-
Duty supported after area margin-
Derated installed capacity minus required duty-
Hot-stream sensible heat rate-
Hot-stream duty minus required duty-
Absolute hot-side balance difference-
Decision view
Q = U A F ΔT area and duty balance
Q = U A F ΔT area and duty balanceCorrected LMTD sets the clean area; the entered fouling allowance expands the design area, which is compared with installed area while the hot-side sensible duty provides an independent energy-balance check.
Exact scenario comparisonCountercurrent log-mean temperature difference (K) changes while all other entered assumptions remain constant.
| Countercurrent log-mean temperature difference (K) | Corrected LMTD F times LMTD | Clean area required by Q over U DeltaT | Required area including fouling margin | Installed area minus design requirement | Design requirement divided by installed area | Duty supported after area margin | Derated installed capacity minus required duty | Hot-stream sensible heat rate | Hot-stream duty minus required duty | Absolute hot-side balance difference |
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How to use Heat Exchanger Preliminary Design Calculator
- Obtain a defensible countercurrent LMTD from terminal temperatures.
- Enter U and a configuration-specific F.
- Add area allowance and cross-check stream duty.
Calculator guide
Understanding Heat Exchanger Preliminary Design Calculator
Heat-exchanger area follows Q=UA(F delta Tlm), but the temperature driving force, correction factor, fouling allowance, and stream energy balance must remain visible.
Detailed calculation process
Detailed heat-exchanger area calculation
The default case checks both UA driving-force capacity and hot-stream sensible duty.
General formula: DeltaT_c=F DeltaT_lmA_c=1000Q/(U DeltaT_c)A_d=A_c(1+m/100)Q_i=UA_iDeltaT_c/[1000(1+m/100)]Q_h=m_h cp_h DeltaT_h The 1000 factor converts kW to W for U in W/m^2 K. The area allowance is kept outside clean U.
What each symbol means
Worked substitution with the default inputs
Dividing 250 kW by U and corrected LMTD returns the clean area; multiplying by 1.20 returns the design area.
Worked situations
Practical examples
- A correction factor below one reduces effective temperature driving force.
- A 20% area allowance multiplies clean area by 1.20 rather than reducing U invisibly.
Better inputs
Useful tips
- Keep kW-to-W conversion explicit.
- Check both hot and cold stream balances in detailed design.
- Use a U value consistent with fluids, construction, and fouling basis.
Before relying on the result
Limitations and common mistakes
- The page does not derive LMTD from four terminal temperatures.
- Pressure drop, phase change, and property variation are excluded.
- Mechanical and code design are outside scope.
Reference
Key terms
- LMTD
- Log-mean terminal temperature difference for the stated flow arrangement.
- Correction factor F
- Configuration adjustment applied to countercurrent LMTD.
- Overall U
- Aggregate heat-transfer coefficient per area and temperature difference.
Important note
Use a qualified thermal and mechanical design for equipment selection; this page is a transparent preliminary area check.
Frequently asked questions
Why enter LMTD?
It must be calculated from the actual terminal temperatures and arrangement, which this preliminary page does not infer.
Is fouling already in U?
Do not double count it; use U and area allowance on a clearly documented basis.
What if hot-side duty differs?
Reconcile flow, properties, temperatures, losses, and phase behavior before sizing.