The effect of cooling conditions on convective heat transfer and flow in a steam-cooled ribbed duct.

This work presents a numerical and experimental investigation on the heat transfer and turbulent flow of cooling steam in a rectangular duct with 90° ribs and studies the effect of cooling conditions on the heat transfer augmentation of steam. In the calculation, the variation range of Reynolds is from 10,000 to 190,000, the inlet temperature varies from 300°C to 500°C and the outlet pressure is from 0.5MPa to 6MPa. The aforementioned wide ranges of flow parameters cover the actual operating condition of coolant used in the gas turbine blades. The computations are carried with four turbulence models (the standard k-ɛ, the renormalized group (RNG) k-ɛ, the Launder-Reece-Rodi (LRR) and the Speziale-Sarkar-Gatski (SSG) turbulence models). The comparison of numerical and experimental results reveals that the SSG turbulence model is suitable for steam flow in the ribbed duct. Therefore, adopting the conjugate calculation technique, further study on the steam heat transfer and flow characteristics is performed with SSG turbulence model. The results show that the variation of cooling condition strongly impacts the forced convection heat transfer of steam in the ribbed duct. The cooling supply condition of a relative low temperature and medium pressure could bring a considerable advantage on steam thermal enhancement. In addition, comparing the heat transfer level between steam flow and air flow, the performance advantage of using steam is also influenced by the cooling supply condition. Changing Reynolds number has little effect on the performance superiority of steam cooling. Increasing pressure would strengthen the advantage, but increasing temperature gives an opposite result. [ABSTRACT FROM AUTHOR]