Gas choked flow

Gas blockage flow occurs when the pressure difference across the control valve exceeds the critical pressure difference. When the pressure difference across the control valve is less than the critical pressure difference, it is normal flow ； When the pressure difference across the control valve increases, if it is greater than or equal to the critical pressure difference, choked flow occurs. You can refer to the formula written by Teacher Mingcidi Dong for the specific formula.

Stall flow refers to the maximum flow rate condition (i.e., the limit condition) reached by incompressible or compressible fluids as they pass through a control valve. Under fixed inlet conditions, when the pressure before the valve P1 remains constant and the pressure after the valve P2 is gradually reduced, the flow rate through the control valve increases up to a maximum limit; further reduction of P2 results in no increase in flow rate. This maximum flow rate is known as the choked flow. After the flow blockage occurs, the relationship between flow rate and △P (P1-P2) no longer follows the rules of the formula. When calculated based on the actual pressure difference. It is much larger than the blocked traffic. Therefore, in order to accurately determine the flow rate at this point, the valve pressure drop at the onset of choked flow must be used as the pressure drop for calculation. Figure 1: Graph of the plug flow relationship. Liquids are incompressible fluids; when plug flow occurs, the Pvc value is related to the physical properties of the liquid medium, namely: Pvc = Ff × Pv, where PV represents the saturated vapor pressure of the liquid ； Ff———the critical pressure ratio coefficient of the liquid. Ff is the ratio of the pressure at the constriction under choked flow conditions to the saturated vapor pressure Pv of the liquid at the valve inlet temperature; it is a function of the ratio of Pv to the critical pressure of the liquid. It can be found in the data table, or calculated using the following formula. It can be seen that as long as the PVC value is determined, it is possible to determine whether an incompressible fluid forms a choked flow. Therefore, when △P is greater than or equal to the valve pressure drop, it is a choked flow condition; when △P is less than the valve pressure drop, it is a non-choked flow condition. For compressible fluids, a coefficient called the pressure difference ratio X is introduced, namely X = △P/P1; in other words, the ratio of the valve pressure drop △P to the inlet pressure P1 is known as the pressure difference ratio. Tests have shown that when air is used as the test fluid, for a given control valve, the pressure difference ratio when choked flow occurs is a fixed constant, known as the critical pressure difference ratio. For other compressible fluids, the critical condition for the onset of choked flow is obtained by multiplying the critical pressure difference ratio by a specific heat ratio coefficient.

It was explained in great detail.