| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 99 === Cavitation in a valve leads to many troubles and inconvenience for factories. It ruins valves in a piping system so that replacing those valves every several months is required. In order to reduce the cost caused by cavitation in a valve, a cage is utilized to make cavitation occur only in the region adjacent to the cage itself. Therefore, it only requires to replace the cage rather than the valve. To validate the design of a cage, simulation of the turbulent flow field inside globe valve and the occurrence of cavitation are necessary for a valve designer. To reach this purpose, prediction of the cavitation inside the globe valve with and without a cage is undertaken in this study. A cavitation model is established in this study. The percentage of vapors in each computational cell is calculated using the proposed cavitation model. Two various cages, the one-stage perforated cage and the one-stage step cage, are considered in this study.
Pressure contours and streamtraces show that the main flow passes through the plug and directly impinges the bottom of a globe valve without a cage in the present numerical results. Consequently, a high pressure region happens at the bottom of the valve. Vortices occur inside the valve body and at the downstream region of the globe valve without a cage while the vortex inside the globe valve with those two cages shrinks. The high pressure region at the bottom of the valve is reduced as well. It is observed that a steep pressure occurs when fluids flow through those cages, but the pressure variation at the
downstream region becomes milder in comparison to the result of the globe valve without a cage. It is found that vapor due to cavitation appears in the vortices existing inside the valve and at the downstream region of the globe valve without a cage. Nevertheless, vapor does not occur in those regions in the globe valve with those two cages. Vapors mainly appear at the exits of the flow passages of those cages. In other words, cavitation inside the globe valve with those two cages mostly occurs in the vicinity of the cages. It prevents that cavitation ruins the valve body and downstream region as those two cages
are installed in the globe valve. In addition to the globe valve, the proposed cavitation model can be applied to prediction of cavitation in other control valve as well.
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