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Linear Instability Analysis of a Water Sheet Trailing from a Wet Spacer Grid in a Rod Bundle
강한옥,Fan-Bill Cheung 한국원자력학회 2013 Nuclear Engineering and Technology Vol.45 No.7
The reflood test data from the rod bundle heat transfer (RBHT) test facility showed that the grids in the upper portion ofthe rod bundle could become wet well before the arrival of the quench front and that the sizes of liquid droplets downstream ofa wet grid could not be predicted by the droplet breakup models for a dry grid. To investigate the water droplet generationfrom a wet grid spacer, a viscous linear temporal instability model of the water sheet issuing from the trailing edge of the gridwith the surrounding steam up-flow is developed in this study. The Orr–Sommerfeld equations along with appropriateboundary conditions for the flow are solved using Chebyshev series expansions and the Tau–Galerkin projection method. Theeffects of several physical parameters on the water sheet oscillation are studied by determining the variation of the temporalgrowth rate with the wavenumber. It is found that a larger relative steam velocity to water velocity has a tendency todestabilize the water sheet with increased dynamic pressure. On the other hand, a larger ratio of steam boundary layer to thehalf water sheet thickness has a stabilizing effect on the water sheet oscillation. Droplet diameters downstream of the spacergrid predicted by the present model are found to compare reasonably well with the data obtained at the RBHT test facility aswell as with other data recently reported in the literature.
LINEAR INSTABILITY ANALYSIS OF A WATER SHEET TRAILING FROM A WET SPACER GRID IN A ROD BUNDLE
Kang, Han-Ok,Cheung, Fan-Bill Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.7
The reflood test data from the rod bundle heat transfer (RBHT) test facility showed that the grids in the upper portion of the rod bundle could become wet well before the arrival of the quench front and that the sizes of liquid droplets downstream of a wet grid could not be predicted by the droplet breakup models for a dry grid. To investigate the water droplet generation from a wet grid spacer, a viscous linear temporal instability model of the water sheet issuing from the trailing edge of the grid with the surrounding steam up-flow is developed in this study. The Orr-Sommerfeld equations along with appropriate boundary conditions for the flow are solved using Chebyshev series expansions and the Tau-Galerkin projection method. The effects of several physical parameters on the water sheet oscillation are studied by determining the variation of the temporal growth rate with the wavenumber. It is found that a larger relative steam velocity to water velocity has a tendency to destabilize the water sheet with increased dynamic pressure. On the other hand, a larger ratio of steam boundary layer to the half water sheet thickness has a stabilizing effect on the water sheet oscillation. Droplet diameters downstream of the spacer grid predicted by the present model are found to compare reasonably well with the data obtained at the RBHT test facility as well as with other data recently reported in the literature.