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Fluid Mechanics
Published in Yeong Koo Yeo, Chemical Engineering Computation with MATLAB®, 2020
When a compressible fluid is stored in a vessel at high pressure, it can escape the vessel at very high velocity to a low-downstream-pressure environment. If the pressure difference between the vessel and the downstream environment is high, the fluid will escape at sonic velocity, which is called a choked flow.43 The flow of a compressible fluid flow can be expressed as follows: Q=53.64Yd2p1∆pKTsg where
Fluid Flow and Pumping Concepts
Published in Marsbed H. Hablanian, High-Vacuum Technology, 2017
Choked flow occurs when sonic velocity is reached in a flow restriction between two pressure regions. For example, if an orifice or a nozzle is installed between two chambers, flow will begin when the pressure in the downstream chamber is lowered. When the ratio of the pressures is approximately 2:1 (for common gases) sonic velocity is established at the orifice or at the throat of the nozzle. Then the volumetric flow through the restriction will remain constant. If the pressure in the upstream chamber is kept constant, the mass flow through the orifice will be at a maximum (for that pressure). The flow-pressure relationship is then simply Q∼P1.
Containment Buildings and the Nuclear Steam Supply System
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
Differential pressure levels in the subcompartment will usually reach a peak value between 25 and 30 PSI. However, the local values of the pressure may be somewhat higher immediately in the vicinity of the pipe break itself. In order to keep these pressure levels from exceeding their maximum design limits, most reactor subcompartments within the containment building are designed with what is known as a blowdown panel. When the pressure level in the subcompartment exceeds the maximum design pressure (which is usually determined by the difference between the maximum pressure and the ambient pressure), the blowdown panel allows the excess pressure to escape to the next largest subcompartment in the reactor containment building. This effectively limits the rate and speed of propagation of the LOCA. One other interesting effect that occurs during a PWR LOCA is that the hot two-phase mixture that leaves the pipe break does so at such a high rate of speed that the flow becomes choked. When this occurs, the rate of propagation of the shock wave cannot exceed the local Mach number Ma = v/c for the water–steam mixture, where v is the velocity of the flow and c is the speed of sound of the mixture. In other words, the velocity of the escaping fluid is limited to a Mach number Ma less than or equal to 1.0 (v ≤ Maof 1.0). In fluid mechanics, this condition is sometimes referred to as choked flow. When the flow becomes choked, the mass flow rate dm/dt from the pipe break is no longer a function of the square root of the pressure difference between the inside and the outside of the pipe.
Effects of blocking ratio and Mach number on aerodynamic characteristics of the evacuated tube train
Published in International Journal of Rail Transportation, 2020
Peng Zhou, Jiye Zhang, Tian Li
Combining (13) and (15) equations, variation curve of throat ratio to Mach number in the critical choked flow state can be plotted as shown in Figure 2. For a certain critical throat ratio corresponding to the incoming flow Mach number, the velocity increase of the incoming flow can inevitably result in the choked flow. In other words, for a critical Mach number, an increase in the throat ratio will inevitably result in the choked flow. By comparing the two limits, it is easily found that isentropic limit and Kantrowitz limit are stricter for subsonic incoming flow and supersonic incoming flow, respectively. Obviously, there will inevitably be choked flow as the Mach number of the incoming flow is about 1.0. In this study, the incoming flow Mach number mainly varies from 0.5 to 1.0, corresponding to the isentropic limit.
The flow and cavitation characteristics of cage-type control valves
Published in Engineering Applications of Computational Fluid Mechanics, 2021
Zhi-xin Gao, Yang Yue, Jia-yi Wu, Jun-ye Li, Hui Wu, Zhi-jiang Jin
Control valves are key components used to regulate flow and pressure in many process industries, such as the nuclear power and thermal power stations. Usually, the volume flow rate of control valves increases monotonously as the pressure drop between the valve inlet and the valve outlet increases, but a choked flow appears when the pressure drop is large. For incompressible working fluid, cavitation or flashing phenomenon is the main reason for choked flow, which can eventually result in valve vibration, noise, or even valve damage.
Sizing charts of helical capillary tubes used in refrigeration and air conditioning
Published in Science and Technology for the Built Environment, 2019
Sukkarin Chingulpitak, Omid Mahian, Ahmet Selim Dalkilic, Lazarus Godson Asirvatham, Somchai Wongwises
The calculation for each section along the capillary tube is performed section by section until the maximum value of entropy is received. At this point, the velocity of fluid is equal to local speed of sound, which is choked flow condition. The pressure of the element, where the entropy reached the maximum value (Pi)s max, is then compared to the evaporator pressure (Pevap) as follows: