KEVOS® MAKEOS · Hydraulics
Heat Exchanger LMTD and Area
What log mean temperature difference and area does this heat exchanger need for the duty?
Log mean temperature difference for counter-flow or parallel-flow exchange, the area needed for a heat duty at an overall coefficient, and a temperature-cross check.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Hot fluid in | °C | Inlet temperature of the hot fluid. |
| Hot fluid out | °C | Outlet temperature of the hot fluid. |
| Cold fluid in | °C | Inlet temperature of the cold fluid. |
| Cold fluid out | °C | Outlet temperature of the cold fluid. |
| Flow arrangement | choice | Flow arrangement (shell-and-tube with several passes needs a correction factor, not included). |
| Heat duty | kW | Heat to transfer. |
| Overall heat transfer coefficient | W/(m²·K) | Overall coefficient for the exchanger type and fluids (oil to water about 200–600 W/m²K). |
Method and formulas
- Counter-flow: ΔT₁ = Th,in − Tc,out; ΔT₂ = Th,out − Tc,in. Parallel: ΔT₁ = Th,in − Tc,in; ΔT₂ = Th,out − Tc,out.
- LMTD = (ΔT₁ − ΔT₂) ÷ ln(ΔT₁ ÷ ΔT₂).
- Area = Q ÷ (U × LMTD).
- Example: the default temperatures give LMTD = 29.72 K and need 1.6824 m² for 20 kW.
Limitations
- Pure counter-flow or parallel flow; multi-pass exchangers need the F correction factor.
- Fouling must be included in U.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size an oil cooler or plate heat exchanger
- Check an existing exchanger for a new duty
- Compare counter-flow and parallel flow
Who it is for
- Process engineers
- Maintenance engineers
- Design engineers
What you get
- Terminal temperature differences
- LMTD
- Area required
Interpreting the result
- Counter-flow needs less area and allows the cold outlet to exceed the hot outlet.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–378. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
