Calculators › Operations, maintenance and commissioning Heat-transfer restoration ratio calculator
Heat-transfer restoration ratio
Use Q = UA × LMTD under the same exchanger geometry and comparable flow regime. Raw heat duty alone cannot establish cleaning effectiveness when the driving temperature difference changes.
Units IP (US) SI (metric)
U A rel = Q after × Δ T lm,clean Δ T lm,after × Q clean \mathrm{UA}_{\text{rel}} = \frac{Q_{\text{after}} \times {\Delta T_{\text{lm,clean}}}}{{\Delta T_{\text{lm,after}}} \times Q_{\text{clean}}} UA rel = Δ T lm,after × Q clean Q after × Δ T lm,clean U A rel = Q after × Δ T lm,clean Δ T lm,after × Q clean \mathrm{UA}_{\text{rel}} = \frac{Q_{\text{after}} \times {\Delta T_{\text{lm,clean}}}}{{\Delta T_{\text{lm,after}}} \times Q_{\text{clean}}} UA rel = Δ T lm,after × Q clean Q after × Δ T lm,clean
Calculator
Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.
Worked example
Given
Q after Q_{\text{after}} Q after 400,000 Btu/h Δ T lm,after {\Delta T_{\text{lm,after}}} Δ T lm,after 20 °F Q clean Q_{\text{clean}} Q clean 550,000 Btu/h Δ T lm,clean {\Delta T_{\text{lm,clean}}} Δ T lm,clean 25 °F U A rel = 400 , 000 × 25 20 × 550 , 000 ≈ 0.9091 \mathrm{UA}_{\text{rel}} = \frac{400{,}000 \times 25}{20 \times 550{,}000} \approx 0.9091 UA rel = 20 × 550 , 000 400 , 000 × 25 ≈ 0.9091
Given
Q after Q_{\text{after}} Q after 160 kW Δ T lm,after {\Delta T_{\text{lm,after}}} Δ T lm,after 16 K Q clean Q_{\text{clean}} Q clean 240 kW Δ T lm,clean {\Delta T_{\text{lm,clean}}} Δ T lm,clean 24 K U A rel = 160 × 24 16 × 240 = 1 \mathrm{UA}_{\text{rel}} = \frac{160 \times 24}{16 \times 240} = 1 UA rel = 16 × 240 160 × 24 = 1
Symbols and units
Symbol Meaning Unit
U A rel \mathrm{UA}_{\text{rel}} UA rel restored-to-clean heat-transfer conductance ratio Q after Q_{\text{after}} Q after heat duty after maintenance Btu/h Δ T lm,after {\Delta T_{\text{lm,after}}} Δ T lm,after post-maintenance log-mean temperature difference °F Q clean Q_{\text{clean}} Q clean clean-reference heat duty Btu/h Δ T lm,clean {\Delta T_{\text{lm,clean}}} Δ T lm,clean clean-reference log-mean temperature difference °F
Symbol Meaning Unit
U A rel \mathrm{UA}_{\text{rel}} UA rel restored-to-clean heat-transfer conductance ratio Q after Q_{\text{after}} Q after heat duty after maintenance kW Δ T lm,after {\Delta T_{\text{lm,after}}} Δ T lm,after post-maintenance log-mean temperature difference K Q clean Q_{\text{clean}} Q clean clean-reference heat duty kW Δ T lm,clean {\Delta T_{\text{lm,clean}}} Δ T lm,clean clean-reference log-mean temperature difference K
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