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A comparative study of the flow field and heat transfer characteristics between swirl and impingement of mist/air cooling on blade leading edge is carried out to find a better cooling configuration for phase transition cooling. The Eulerian–Lagrangian particle tracking technique is used to investigate mist/air cooling. Comparisons are made between these two cooling forms in such aspects as vortex structure, heat transfer enhancement, pressure loss, and thermal uniformity with and without mist injection. The influences of mist ratio and Reynolds numbers on these parameters are studied in this paper. Results show that heat transfer is enhanced while pressure loss and thermal uniformity are improved by the swirl flow created by vortex impingement. The heat transfer performance increases by about 46.2 and 51.9%, respectively, for impingement and swirl cooling with 8% mist injection, and the pressure loss coefficient increases by 19%. The difference of heat transfer coefficient between swirl and impingement cooling with and without mist injection at high Reynolds number is larger than that at low Reynolds number. In addition, the heat transfer nonuniform coefficient of swirl cooling is about 15% lower than for impingement cooling. [ABSTRACT FROM PUBLISHER]

Jet impingement cooling is usually used in zones with extremely high thermal loads. The major factor that limits impingement heat transfer uniformity is the crossflow. The impingement cooling with return hole is applied to reduce the negative effect of crossflow on the target surface heat transfer in present paper. The influences of jet-to-plate spacing (H / D), impingement target surface curvature (α), temperature ratio (TR) and Reynolds number on flow field and heat transfer performance are investigated in detail. The results indicate that the correlation between the overall area average Nusselt number of target surface and H / D , the overall area average Nusselt number decreases by approximately 5.76% with H / D increases by one unit. Increasing the impingement target surface curvature is beneficial to expand the spanwise heat transfer. The overall area average Nusselt number increases by 295.5% for Reynolds number varying from 10,000 to 50,000 at TR = 0.910, and the overall area average Nusselt number increases by 8.68% for the TR varying from 0.668 to 0.910 at Re = 30,000. The results indicate that impingement cooling with return hole can achieve high heat transfer coefficient and uniform heat transfer distribution. [ABSTRACT FROM AUTHOR]

• Applicability of fluid dynamics theory to helium is demonstrated. • Flow characteristics with Reynolds number of helium boundary layer are performed. • Effect of FST on transitional helium boundary are investigated. • Similarities and differences between the helium and air boundary layers are researched. This paper investigates the fundamental flow behaviors of helium, aiming at supporting the helium turbomachinery design optimization in generation Ⅳ nuclear power station. The applicability of hydrodynamics theory to helium has been discussed from many aspects including continuous medium, Newtonian fluid, Stokes hypotheses, and perfect gas state. The Reynolds average N-S method (RANS) with the γ-θ transition model is used for solving the compressible helium boundary layer. The influence of the Reynolds number on the helium boundary layer transition is explored. With the increasing Reynolds number, the transition of boundary layer occurs in advance on the plate. On the other side, the boundary layers under different Reynolds numbers have uniformity in the comparison of dimensionless parameters. The free stream turbulence (FST) is a main influence factor on the transition. Both the enhanced turbulence intensity and the large turbulence scale can make the transition be triggered in advance and reduce the onset Reynolds number. For the fluids with different specific heat ratios, the helium transition lags behind the air under the same Mach number. When under the same Reynolds number, the helium boundary layer is identical to the air. They share the same mean velocity profile and agree with the theory solution and experimental data simultaneously. [ABSTRACT FROM AUTHOR]