Indirect dry cooling, natural draft, vertical bundles
Cools a condenser's circulating water in bundles standing around the inlet of a natural-draft tower.
The same loop cooled in bundles standing around the tower inlet, as the direct system arranges them. The air crosses the bundles horizontally, the buoyancy datum is their mid-height, and the vena contracta of the ring costs more at the inlet than a lintel does. Built, but not yet verified against a worked example.
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 vertical bundles | An independent implementation of the same specification (another model, not a measurement) | Air mass flow rate within 0.7%, heat transfer rate within 0.2% |
| 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. On a vertical ring the draft-side coefficients carry a multiplier of 0.5, measured on the air mass flow rate of four CFD series. 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
- Another modelKong's conventional indirect ring under crosswind: the air flow of an indirect ring wants the same k = 0.5
- Another modelIndirect natural-draft tower with vertical bundles, against an independent implementation
- Measurement, rigWei's wind tunnel on a Heller ring: the pressure coefficients want 0.62, the heat-side correction wants nothing
- Another modelZhao's Heller tower under crosswind at constant loadA third family, and a third multiplier