Indirect dry cooling, natural draft, horizontal array
Cools a condenser's circulating water in bundles lying in the inlet of a natural-draft tower.
A circulating-water loop cooled in A-frame bundles lying in the inlet plane of a natural-draft tower, the arrangement of Kröger's Section 7.1. The loop node gives the water mass flow rate and its inlet temperature, or closes the loop on a condenser stated by its terminal temperature difference or its conductance, which gives the back pressure.
Pack: Natural 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
- 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 and water outlet temperature of an indirect tower with a horizontal array | Kröger's worked Example 7.3.1 | Heat transfer rate within 0.024%, air mass flow rate within 0.010%, both outlet temperatures within 0.005 K |
| Discretised transient | Water temperature, air temperature inside the tower and heat transfer rate through a start-up or a load change | The measured cold start of the 20 m Gatton tower (Dong et al., 2021) | Water temperature within 2.7 K RMS and the air inside the tower within 4.1 K over 2 000 s |
Its limits
Crosswind on a natural-draft tower is represented by the method of Kröger, Vol. 2, Section 9.2: mean inlet and outlet pressure coefficients in the draft equation and a maldistribution factor on the heat transfer rate, fitted on horizontal bundles filling the inlet. The heat transfer rate lost per unit of air flow is where the CFD literature disagrees, by 0 to 18% from 6 m/s upward, and every report of a windy case states this. On an indirect tower whose tube wall is resolved, the factor acts through a multiplier on the air-side conductance, solved so the one-cell relation gives Kröger's corrected heat transfer rate, so the walls and the air carry it. Not modelled for this system: fouling that develops in service and degradation (a stated fouling resistance is carried as given), freezing and freeze protection, hybrid or adiabatic inlet assistance, 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
- Measurement, rigDong et al. 2021The Gatton tower's start-up from cold
- Measurement, rigDong et al. 2021The Gatton tower's steady end-state, from a second campaign
- Worked exampleKröger Example 7.3.1 closed on its own heat transfer rate: the loop returns his water temperature
- Measurement, plantKendal under crosswind: the printed method against a full-scale plant, and against its own author's model
- Worked exampleKröger Example 7.3.1Indirect natural-draft tower, horizontal array
- Worked exampleKröger Example 9.2.1The same tower with its A-frames laid flat
- Worked exampleKröger Example 9.2.2The horizontal array under a 6 m/s crosswind
- Measurement, rigGatton 20 m NDDCT: the best system case in the library, and why it still cannot carry model-form uncertainty