Gatton 20 m NDDCT: the best system case in the library, and why it still cannot carry model-form uncertainty
Tier 2: measurement on a controlled rig.
System: Indirect dry cooling, natural draft, horizontal array
- What was compared
- The heat transfer rate, the air mass flow rate and the air temperature rise of a 20 m natural-draft dry cooling tower with a horizontal array of round finned tubes, at the eleven of fourteen measured steady points the model solves over an ambient of 11.6 to 30.4 °C, with the water inlet temperature and flow set from each point.
- Against
- Measurements on the operating tower at Gatton by Li et al. (2017, Tables 2 to 5), with every sensor accuracy stated and a reference uncertainty of 6.1%; a measurement on a plant.
- The agreement
- On the default air-side relations the model over-predicts the heat transfer rate by 17.9% and the air mass flow rate by 19.2% on average, while the air temperature rise is within 1.1%, so the error lies in the draft. With the paper's own bundle loss coefficient the over-predictions fall to 5.9% and 3.0%, and with Ganguli's loss relation (Kröger, Eq. 5.5.9) to 8.9% and 6.9%.
- What it shows
- The case records a disagreement of known size, attributed to the bundle loss relation, the draft framework and an unmodelled leak at the bundle seals, and it contributes nothing to a model-form uncertainty band. The tower's in-line bundle runs below the Reynolds number range of every bundle loss relation with a measured accuracy, and every air-side relation available was fitted to staggered bundles.
- Source
- X. Li, S. Duniam, H. Gurgenci, Z. Guan, A. Veeraragavan, 'Full scale experimental study of a small natural draft dry cooling tower for concentrating solar thermal power plant', Applied Energy 193 (2017) 15-27Sections 2.1-2.4 and 3.3, and Tables 1-5. Section 4's power-cycle model and the refined 1-D model of Section 3.4 are not used - the latter cannot be reproduced, because its fitted leak factor is never printed.