Air-cooled heat exchanger, induced draft
Cools a process fluid in horizontal finned-tube bundles, with fans above drawing the air through them.
The same bay with its fans above the bundles, drawing the heated air. The shaft power is higher for the same heat transfer rate and the air distribution is more uniform.
Pack: Mechanical draft. In the plans: Pro (as its one pack), Expert, Enterprise and Academic. Plans
The analyses it offers
- RatingThe plant at one condition, solved once.
- DesignFix a target and solve for one dimension.
- Parametric sweepThe rating repeated along one or more axes.
- Annual runThe rating once per weather point over a year.
- Transient simulationThe plant after an event.
The transient scenarios
- Fan start from rest
- Fan stop
- Step on one boundary channel
- Step in the ambient temperature
- The ambient temperature following a profile
What it predicts, and what that was compared with
The app's capability statement for this system, as every report prints it.
| Analysis | Predicts | Compared with | Agreement |
|---|---|---|---|
| Steady rating, and the sweep, design and annual runs built on it | Air mass flow rate, heat transfer rate, fan power and outlet temperatures of a fan-driven bay or bank, still or under wind | Kröger's worked Examples 8.1.1 and 8.1.2, and 9.3.1 and 9.3.2 under wind | Air mass flow rate within 0.10%, heat transfer rate and fan power within 0.04%, temperatures within 0.04 K; under wind within 1.5% and 0.5% |
| Discretised transient | Fluid outlet temperature, heat transfer rate and air mass flow rate through a fan ramp or a load change | Its own steady rating, the state it settles to; no measured start-up or run-down | Settles to the steady rating within 0.1% on the air mass flow rate and the heat transfer rate |
Its limits
Wind on a fan-driven bank is Kröger's Section 9.3 procedure on Duvenhage's CFD tables, held constant beyond 3 m/s at 5.7 m, without any representation of the site. Not modelled for this system: hot-air recirculation between streets, fouling that develops in service and degradation (a stated fouling resistance is carried as given), freezing and freeze protection, and the plume. Every correlation is a fit over a declared range; the report lists any excursion at the solved state, and a result outside a declared range is an extrapolation and not a prediction.
The validation cases of this system
- Worked exampleKröger Example 8.1.2Induced-draft air-cooled heat exchanger bay