Evaluation of Enhanced Heat Transfer Within a Four Row Finned Tube Array of an Air Cooled Steam Condenser

Abstract

Air cooled steam condensers (ACSC) consist of finned-tube arrays bundled in an A-frame structure. Inefficient performance under extreme temperature operating conditions is a common problem in ACSCs. The purpose of this study was to improve the heat transfer characteristics of an annular finned-tube system for better performance in extreme climatic conditions. Perforations were created on the surface of the annular fins to increase heat transfer coefficient (h). Mesh generation and finite volume analyses were performed using Gambit 2.4.6 and Fluent 6.3 with an RNG k–ϵ turbulent model to calculate pressure drop (ΔP), heat flux (q), and heat transfer coefficient (h). Solid (no perforations) finned-tubes were simulated with free stream velocity ranging between 1 m/s–5 m/s and validated with the published data. Computations were performed for perforations at 30° interval starting at ±60°, ±90°, ±120°, ±150°, and ±180° from the stagnation point. Five cases with single perforation and three cases with multiple perforations were evaluated for determining the maximum q and h, as well as minimum ΔP. For the perforated case (perforations starting from 60° at interval of 30°), the fin q and h performance ratios increased by 5.96% and 7.07%, respectively. Consequently, the fin ΔP performance ratio increased by 11.87%. Thus, increased q and h is accompanied with a penalty of higher ΔP. In contrast, a single perforation location at 120° provided favorable results with a 1.70% and 2.23% increase in q and h performance ratios, respectively, while there was a relatively smaller increase (only 1.39%) of ΔP performance ratio. Perforations in the downstream region at ±120°, ±150°, and ±180° also resulted in a similar favorable outcome. Furthermore, the spacing of the fins along the arms of an A-frame ACSC was altered to decrease ΔP across the finned-tube array. Fin spacing in the A-frame structure with sparsely spaced fins in the center resulted in a 1.80% reduction in ΔP. Thus, penalty in ΔP for a perforated fin can possibly be offset by changing the fin spacing along the arms of an A-frame structure.

Acknowledgments

Rupak K Banerjee and Madhura Karve have contributed equally to this article. Madhura Karve implemented the mathematical analyses, numerical calculations, and drafted initial versions of the article under the supervision of Rupak K: Banerjee. Dong Lee, Jong Ha, and Young Cho provided technical insights into this research during model design and numerical data analysis. Madhura Karve could not effectively complete the rebuttal and implement the modifications based on the reviewer's comments within the stipulated time because of her commitment with her new employer. In light of this, Rupak K. Banerjee, with the assistance of Marwan Al-Rjoub, Anup Paul and Kranthi Kolli, completed the rebuttal that was acceptable to the other co-authors.

Notes

*Indicates favorable fin performance values.

*Indicates favorable fin performance values.

*indicates favorable change in ΔP.