GIFSQ Tools · Module 17 — Food Processing, Thermal Engineering & Utilities · Tool 333 of 500
Work out the overall heat transfer coefficient U of a heat exchanger from its duty, area and the hot and cold stream temperatures, using the log mean temperature difference.
Try sample values — fills the form with the worked example below.
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LMTD (°C)
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U (W/m²·K)
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Heat flux (kW/m²)
Equation: LMTD = (ΔT₁ − ΔT₂) ÷ ln(ΔT₁ / ΔT₂), with ΔT₁ = hot in − cold out and ΔT₂ = hot out − cold in; U = Q ÷ (A × LMTD).
Method: Log mean temperature difference method for heat exchangers (Incropera and DeWitt, Fundamentals of Heat and Mass Transfer).
Assumptions: steady state; constant overall coefficient; counter-current or co-current flow with the stated end differences; no phase change.
Limitations: multipass and cross-flow exchangers need an LMTD correction factor F, which this tool does not apply; fouling lowers the real U over time.
Rounding: LMTD, U and heat flux to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Log mean temperature difference method for heat exchangers (Incropera and DeWitt, Fundamentals of Heat and Mass Transfer).
Assumptions: steady state; constant overall coefficient; counter-current or co-current flow with the stated end differences; no phase change.
Limitations: multipass and cross-flow exchangers need an LMTD correction factor F, which this tool does not apply; fouling lowers the real U over time.
Rounding: LMTD, U and heat flux to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 500 kW over 20 m², hot 90 → 60 °C, cold 20 → 50 °C: both end differences are 40 °C, so LMTD = 40.00 °C and U = 625.00 W/m²·K.
Enter values above to see results.
Typical U: water-to-water 1000–2500, steam-to-water 1500–4000, viscous food to water 200–1000 W/m²·K. Tool 333 of 500 — GIFSQ
