NUMERICAL INVESTIGATION OF EFFECT OF HELIX ON HIGH-SPEED STEAM CONDENSATION IN SQUARE/CIRCULAR CHANNELSRenkun Dai 摘要The present study focuses on the effect of helix on condensation in square/circular channels while the steam inlet velocity is as high as 100m·s^{-1}. Three-dimensional physical models with the same axial length and hydraulic diameter but different helical parameters, including helical angles, helical diameters, helical distances, are established. Numerical method based on the VOF(volume of fluid) method, coupled with the SST k-ω turbulent flow model, is adopted. Moreover, a user-defined function defining the phase change is interpreted in the numerical method and the phase interface temperature is correspondingly assumed to be the saturation temperature as the condensation proceeds. Results indicate that the maximum velocity is much higher and the high velocity region is much larger in the helical channel. Outlet steam quality is mainly dependent on helical angle, it declines when the helical angle decreases. Under the same axial length, smaller helical angle results in larger heat exchange area which reinforces the condensation process. With the decrease of helical angle, the condensation heat transfer coefficient increases at first and then decreases, implicating that a best helical angle may exist that could strengthen the heat transfer efficiently. The best helical angle among the square and circular channels is different, hopefully that may provide guidance for industrial applications. |
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