Critical pressure ratio of the hottest safety valv

The critical pressure ratio of safety valve

correctly calculating the displacement of safety valve is an important basis for selecting safety valve reasonably and judging its reliability. From the 400 cases of GB project, there is great potential for electromechanical improvement. Nearly in 1.5 9 "steel pressure vessels", and plug socket, contactor, circuit breaker and other components, according to the different flow state of safety valve, put forward two kinds of displacement calculation formulas. Therefore, judging whether the safety valve is in the critical flow state or subcritical flow state is the premise of correctly selecting the displacement calculation formula. At present, there are two views on the value of the critical pressure ratio of the safety valve: ① in the specifications of various countries, it is considered that the critical pressure ratio of the safety valve is the same as that of the nozzle, and its value is 0.528 [1,2]. ② Many experts and researchers believe that the critical pressure ratio of safety valve is less than that of nozzle, and its value is about 0.2 ~ 0.3 [3]

critical pressure ratio RCR refers to the ratio of inlet and outlet pressure when the airflow velocity reaches the local sound speed at the minimum channel section. In theory, the critical pressure ratio of nozzle can be determined by formula calculation. When the outlet inlet pressure ratio of the nozzle is lower than or equal to the critical pressure ratio of the nozzle, because the outlet section is already sonic flow, the disturbance of the outlet inlet pressure ratio cannot exceed the sonic surface, so the disturbance cannot affect the flow in the nozzle. The gas flow pressure on the outlet section remains unchanged at p2/p1= RCR, the gas flow on the outlet section is still sonic flow, and the relative displacement remains unchanged, that is, w/wmax=1. At this time, the nozzle is in a critical or supercritical flow state [4]. In addition to the nozzle, the critical pressure ratio of other structures often needs to be determined by the test, and the critical pressure ratio determined by the test that CNTs has a very large aspect ratio is called the second critical pressure ratio for distinction

due to the complexity of the safety valve structure, it is difficult to determine the airflow velocity at the minimum channel cross-sectional area of the safety valve, so it is impossible to accurately determine the critical pressure ratio of the safety valve according to whether the minimum channel cross-sectional area reaches sonic speed. At present, the method to judge whether the safety valve reaches the critical flow state is to measure the discharge coefficient of the safety valve. It is believed that as long as the discharge coefficient does not change with the pressure ratio, the safety valve will reach the critical flow state [3]. The measured result is that the displacement of the safety valve always changes with the change of the pressure ratio, but when the pressure ratio of the safety valve is lower than 0.2 ~ 0.3, the displacement of the safety valve changes less with the pressure ratio, and people believe that this small change is caused by the measurement error, so it is judged that the critical pressure ratio of the full open safety valve is about 0.2 ~ 0.3. The theoretical basis of this test method for determining the critical pressure ratio of safety valve is that under critical and supercritical flow conditions, the pressure ratio disturbance cannot exceed the sonic surface, while the relative displacement of nozzle remains unchanged, that is, w/wmax=1. However, in the past few years of critical or supercritical flow state, the flow in the nozzle outlet section has been sonic flow, so that the relative displacement w/wmax remains unchanged. On the contrary, if the relative displacement remains unchanged, it is judged that the flow in the outlet section is sonic flow, and the safety valve is in critical flow state, which lacks theoretical basis and experimental proof. (end)