Choking condition

Addition of 15% gasoline to methanol to produce M85 fuel is an alternative. At temperatures above —6.7° C, reHable ignition of M85 fuel occurs because the gasoline provides the vapor phase necessary for ignition under choked condition. 

Note that under choked conditions, the exit velocity is V = V = c = V/cKTVM not V/cKT(/M, . Sonic velocity must be evaluated at the exit temperature. For air, with k = 1.4, the critical pressure ratio p /vo is 0.5285 and the critical temperature ratio T /Tq = 0.8333. Thus, for air discharging from 300 K, the temperature drops by 50 K (90 R). This large temperature decrease results from the conversion of internal energy into kinetic energy and is reversible. As the discharged jet decelerates in the external stagant gas, it recovers its initial enthalpy. 

When the flow is choked, G = G is independent of external downstream pressure. Reducing the downstream pressure will not increase the flow The mass flow rate under choking conditions is directly proportional to the upstream pressure. 

DIAGNOSTICS OUTPUTS Compressor Efficiency Lower than Design Compressor Approaching Surge Conditions Compressor Approaching Choke Conditions Dirty Compressor... 

In the analysis of published data on choking conditions in valves of several different types in the size range 50-250 mm. Lush found that when ffoch related to by the following expression good agreement was obtained ... 

Wmax = maximum mass flow at critical or choked conditions, lb/sec... 

Since a downflow in flooding is under the choked condition by the upward-moving void, the void may become stagnant along the wall. Thus the heat transfer... 

The scope of coverage includes internal flows of Newtonian and non-Newtonian incompressible fluids, adiabatic and isothermal compressible flows (up to sonic or choking conditions), two-phase (gas-liquid, solid-liquid, and gas-solid) flows, external flows (e.g., drag), and flow in porous media. Applications include dimensional analysis and scale-up, piping systems with fittings for Newtonian and non-Newtonian fluids (for unknown driving force, unknown flow rate, unknown diameter, or most economical diameter), compressible pipe flows up to choked flow, flow measurement and control, pumps, compressors, fluid-particle separation methods (e.g.,... 

Determine Echoed from Equation 5-64 to confirm operation at choked conditions. 

A simple interpretation of this choking condition is as follows. The gas flows as a result of the pressure difference P — P2. When the gas speed reaches the speed at which a pressure wave propagates relative to the gas, any pressure wave generated will be unable to travel upstream but will remain stationary relative to the pipe. Thus, if the pressure in the reservoir into which the gas discharges is reduced below Pw, the fact cannot be transmitted upstream and so the flow rate will not change. 

An adaptation of Eq. (14.38) for a nozzleless rocket indicates that the port area increases as the burning surface of the propellant regresses, decreases and Aj increases, and so the choked condition is varied. Thus, the thrust generated by the nozzleless rocket is determined by the relationship of the mass generation rate in the port and the mass discharge rate at the rear-end of the port.I - l... 

When the gas injection nozzle is in an unchoked condition, the pressure in the gas generator is equal to the combustion chamber pressure, i. e., pg = p The gas generation rate is determined by the pressure in the combustion chamber. When the gas injection nozzle is in a choked condition, the burning rate is determined by the gas injection nozzle area, A g, and then the pressure in the gas generator, pg, is determined by... 

The exit Mach number M2 may not exceed unity. M2 = 1 corresponds to choked flow sonic conditions may exist only at the pipe exit. The mass velocity G in the charts is the choked mass flux for an isentropic nozzle given by Eq. (6-118). For a pipe of finite length, the mass flux is less than G under choking conditions. The curves in Fig. 6-21 become vertical at the choking point, where flow becomes independent of downstream pressure. 

Under choked conditions, the maximum flux of gas through the valve is q ... 

Introducing the general correlation for the friction factor suggested by Churchill (11), figure 2 shows how the choking conditions now depend on the pipe length for isothermal conditions and variable friction factor. As it is seen, the effect of the variable friction factor is negligible. 

Solution of Eq. (6-114) for G and differentiation with respect to p reveals a maximum mass flux G = pj/Mj,l(RT) and a corresponding exit velocity = VRTTMO) and exit Mach number = 1/w. This apparent choking condition, though often cited, is not physically meaningful for isothermal flow because at such high velocities, and high rates of expansion, isothermal conditions are not maintained. 

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