Air-cooled heat exchanger, forced draft
Cools a process fluid in horizontal finned-tube bundles, with fans below pushing the air through them.
A bay of horizontal bundles above its fans, cooling a process fluid or circulating water. The heat added by the fan reaches the bundle.
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 8.1.1Forced-draft air-cooled heat exchanger bay
- Worked exampleKröger Example 8.3.1A forced-draft bank of six bays
- Worked exampleKröger Example 8.4.1Plume recirculation on a forced-draft bank
- Worked exampleKröger Example 9.3.1The six-bay bank under a 3 m/s crosswind
- Worked exampleKröger Example 9.3.2The six-bay bank under a 3 m/s wind along its axis