Heat exchanger fouling and cleaning
Actual U and fouling resistance from a field test — and how much duty, money and time the fouling is costing you.
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Need the full version for your plant?
The Shell and Tube Heat Exchanger Performance and Fouling Excel tool does everything here and more: actual U, fouling resistance and cleanliness from plant readings — with the duty lost to fouling, its yearly cost and the best cleaning interval. Print-ready report, any units, visible formulas, no macros.
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How this calculator works
From your test readings, the calculator works out the duty, the corrected mean temperature difference and the actual overall coefficient: U = duty ÷ (area × F × LMTD). The fouling resistance is the difference between the actual and the clean resistance: Rf = 1/Unow − 1/Uclean.
To see what fouling costs, the exchanger is re-rated by the effectiveness-NTU method at the clean U with the same flows and inlet temperatures. The difference in duty is the heat lost to fouling. Valued at your fuel or steam price, it gives a yearly cost and the number of days a cleaning takes to pay back.
The example uses the same heat-recovery exchanger as the LMTD calculator, 80 m², clean U 600 W/m²·K. The test gives U = 408 W/m²·K (68 % of clean) and Rf = 0.00078 m²·K/W — more than twice the 0.00035 allowed in design. A clean exchanger would recover about 350 kW more, worth about USD 89,000 a year at USD 30/MWh, so a USD 6,000 cleaning pays back in under a month.
Limits: fouling assumed to be the only change since the clean U; constant specific heats, no phase change. References: Perry's Chemical Engineers' Handbook §11; Kern, Process Heat Transfer; Heat Exchanger Design Handbook; TEMA Standards (fouling resistances).