Dyehouse Heat Exchanger Fouling & Thermal Loss Predictor

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 10 inputs are read from the form on every keystroke: Clean Heat Transfer Coefficient, Fouling Resistance, Heat Transfer Area, Hot Side Inlet, Hot Side Outlet, Cold Side Inlet, Cold Side Outlet, Operating Hours per Year, Average Load Factor and Heat Cost.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Fouled Heat Transfer Coefficient together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Clean Duty, Fouled Duty, Capacity Lost, Log Mean Temperature Difference, Energy Not Recovered and Annual Cost of Fouling — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

The tool loads with this case already solved — the Fouled Heat Transfer Coefficient shown above is its answer. Change one value and the difference from this baseline is the sensitivity of the result to that variable.

How to use it

1. Work through the input groups in order — Exchanger and Duty & Cost. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Fouled Heat Transfer Coefficient in the dark results panel — that is the headline figure, expressed in W/m²K.
4. Check the supporting rows underneath (Clean Duty, Fouled Duty, Capacity Lost, Log Mean Temperature Difference, Energy Not Recovered and Annual Cost of Fouling) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Fouled Heat Transfer Coefficient before a trial is booked, so machine time and material in Advanced Utility & Power Quality are committed against a calculated figure rather than an estimate.
• Costing and quotation — Fouled Heat Transfer Coefficient is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Clean Heat Transfer Coefficient) shows how much of the gap in Fouled Heat Transfer Coefficient each variable explains.
• Teaching and study — the accepted ranges bracket normal Advanced Utility & Power Quality practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Assumptions and limits

• Duty is computed at fixed terminal temperatures, which is the design case rather than what a fouled exchanger actually does — in service the outlet temperatures move instead and the true shortfall must come from measured temperatures on both sides. The load factor matters more than any other input for the cost figure and should be taken from flow logs, not assumed. Counter-current flow is assumed for the LMTD; a co-current or multi-pass arrangement needs its own correction factor. Fouling resistance itself grows over a cleaning cycle rather than sitting at one value, so run this at the end-of-cycle figure to size the cost of deferring a clean.
• Every input is bounded to the range normal practice occupies (Clean Heat Transfer Coefficient 200 to 8000 W/m²K, Fouling Resistance 0 to 0.005 m²K/W and Heat Transfer Area 0.5 to 500 m², and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Questions people ask