Abstract
For the large scale air-cooled heat exchanger of a natural draft dry cooling system (NDDCS) in power plants, its thermo-flow characteristics are basically dominated by crosswinds. Unfortunately however, the detailed mechanisms of the crosswind effects have yet to be fully uncovered. Therefore, in this research, the local flow and heat transfer performances of the cooling deltas, which are also termed as the fundamental cells of the large-scale air-cooled heat exchanger, are specifically investigated with full consideration for the cell structure and the water-side temperature distribution at various wind speeds. A 3D CFD method with a realizable k-ε turbulence model, heat exchanger model, and porous media model is developed, and the accuracy and credibility of the numerical model are experimentally validated. With the numerical simulation, the overall 3D outlet air temperature of the large-scale air-cooled heat exchanger, and the corresponding local air velocity and temperature fields of the cooling deltas are qualitatively analyzed. Furthermore, the air-mass flow rate and heat rejection are also quantitatively studied at both the global and local views. The results depict that with an increase in the wind speed, the air mass flow rate and heat rejection will increase greatly for the frontal deltas; however, they will drop dramatically for the middle-front deltas. As for the middle- as well as the middle-rear deltas, the thermo-flow performances vary markedly at various wind speeds, which behave in the most deteriorated manner at a wind speed of 12 m/s. The rear deltas show the best thermo-flow performances at a wind speed of 12 m/s, but the worst at 16 m/s. A detailed analysis of the variable fields for each cooling delta may contribute to the performance improvement of the large-scale air-cooled heat exchanger of NDDCS.
Highlights
In thermal and nuclear power plants, the natural draft-dry cooling system (NDDCS) has been adopted throughout the world, which shows significant water conservation, compared with the wet-cooling system, with a closed circulating water circulation [1,2]
The wind effects on the thermo-flow characteristics of natural draft dry cooling system and corresponding approaches have been thoroughly investigated, the aforementioned studies only focused on the overall analysis of the large scale air-cooled heat exchanger, and they have not yet determined the detailed velocity or temperature fields of the cooling deltas for various air-cooled sectors been fully disclosed at various wind speeds
With the macro heat exchanger model, the 3D overall outlet temperature fields are presented for for a large-scale air-cooled heat exchanger, and the quantitative thermo-flow performances are a large-scale air-cooled heat exchanger, and the quantitative thermo-flow performances are compared at various wind speeds
Summary
In thermal and nuclear power plants, the natural draft-dry cooling system (NDDCS) has been adopted throughout the world, which shows significant water conservation, compared with the wet-cooling system, with a closed circulating water circulation [1,2]. The wind effects on the thermo-flow characteristics of natural draft dry cooling system and corresponding approaches have been thoroughly investigated, the aforementioned studies only focused on the overall analysis of the large scale air-cooled heat exchanger, and they have not yet determined the detailed velocity or temperature fields of the cooling deltas for various air-cooled sectors been fully disclosed at various wind speeds. In this research, the macro heat exchanger model for the finned tube bundles are adopted, so as to investigate the thermo-flow characteristics of the air-cooled sectors and cooling deltas with the numerical method, which differs from the CFD method with the previous radiator model. This research provides quite a comprehensive investigation of the large-scale air-cooled heat exchanger, which may contribute to more targeted approaches towards the performance improvement of the natural draft dry cooling system
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