Heat Exchanger Fouling & Derating Calculator
Determine clean versus fouled overall U-values, total fouling resistance (Rf), required excess surface area over-design margin, and cleanliness factors per TEMA.
Clean Heat Transfer Coefficient
TEMA Fouling Resistances (Rf)
Fouled Derating Performance
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Frequently Asked Questions
What is a fouling factor (Rf) in heat exchanger design?
The fouling factor (Rf) is the thermal resistance caused by the accumulation of deposits, mineral scale, algae, biological slime, or corrosion products on heat transfer surfaces over time, expressed in hr·ft²·°F/BTU (or m²·K/W). It derates the overall heat transfer coefficient: 1/U_fouled = 1/U_clean + Rf.
Why should heat exchangers not be excessively oversized for fouling?
While adding extra surface area compensates for future fouling, oversizing a heat exchanger increases internal cross-sectional area and lowers fluid velocity. Lower fluid velocity (< 3 to 4 ft/s) drastically accelerates sediment settling and biofouling, causing the unit to foul much faster than an optimally sized unit.
What is the Cleanliness Factor (CF)?
Cleanliness Factor is the ratio of the fouled overall heat transfer coefficient to the clean coefficient expressed as a percentage: CF = (U_fouled / U_clean) × 100%. Power plant surface steam condensers typically specify a design Cleanliness Factor of 85%.