| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 101 === The purpose of this study is focused on the volume suitability of portable test vessel for a safety valve. When the pressure within the container has reached its limit, the safety valve quickly releases the excess pressure to protect the container from explosion due to overpressure; therefore, the safety valve is very important pressure equipment on the high pressure container. The safety valve should be removed from the test vessel and calibrated by the licensed manufacture or institution periodically; and it is convenient to have a portable testing equipment for the on-site inspection or test. Therefore, the volume suitability of the portable vessel for safety valve is needed to increase the accessibility of the on-site testing and will be the focus of the present study.
By assuming a steady, one-dimensional, inviscid and compressible flow with isentropic process through a convergent-divergent nozzle, the control volume analysis based on the mass conservation and the energy equations is employed to derive the time elapse of a specific blown-down condition for various sizes and shapes of the pressure vessel. The theoretical predictions and the experimental results will be compared to make a proper decision on the volume and shape suitability for the purpose of on-site testing. By retrieving the blown-down pressure curve, there are various processes such as "acute drop", "acute rise", "irregular run-out", "chattering", "run-out" and irregular run-out and regular oscillation before the disk of the pressure valve closes. The irregularity run-out and chatter of the blown-down pressure curve shall be avoided in order not to damage the disk and the valve seat of the safety valve. The blown-down pressure curves based on the theoretical predictions and the experiments coincide quite well with suitable overpressure. Among the models tested, the volume suitability of the pressure vessel is selected based on examining the characteristics of blown-down pressure curve and the size or weight of the vessel.
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