# choked flow

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## Choked flow

Fluid flow through a restricted area whose rate reaches a maximum when the fluid velocity reaches the sonic velocity at some point along the flow path. The phenomenon of choking exists only in compressible flow and can occur in several flow situations. See Compressible flow

#### Through varying-area duct

Choked flow can occur through a convergent flow area or nozzle attached to a huge reservoir. Flow exits the reservoir through the nozzle if the back pressure is less than the reservoir pressure. When the back pressure is decreased slightly below the reservoir pressure, a signal from beyond the nozzle exit is transmitted at sonic speed to the reservoir. The reservoir responds by sending fluid through the nozzle. Further, the maximum velocity of the fluid exists at the nozzle throat where the area is smallest.

When the back pressure is further decreased, fluid exits the reservoir more rapidly. Eventually, however, the velocity at the throat reaches the sonic velocity. Then the fluid velocity at the throat is sonic, and the velocity of the signal is also sonic. Therefore, further decreases in back pressure are not sensed by the reservoir, and correspondingly will not induce any greater flow to exit the reservoir. The nozzle is thus said to be choked, and the mass flow of fluid is a maximum. See Mach number, Sound

#### With friction

Choked flow can also occur through a long constant-area duct attached to a reservoir. As fluid flows through the duct, friction between the fluid and the duct wall reduces the pressure acting on the fluid. As pressure is reduced, other fluid properties are affected, such as sonic velocity, density, and temperature. The maximum Mach number occurs at the nozzle exit, and choked flow results when this Mach number reaches 1.

A reservoir with a constant-area duct attached may also be considered in the case that the flow through the duct is assumed to be frictionless but heat is added to the system along the duct wall. See FLuid flow, Gas dynamics

## choked flow

[¦chōkt ′flō]
(fluid mechanics)
Flow in a duct or passage such that the flow upstream of a certain critical section cannot be increased by a reduction of downstream pressure.
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Earlier in the day, the defence minister also said that the move to scrap high-value currency notes choked flow of funds to the terrorists and reduced stone-pelting incidents in the Jammu and Kashmir.
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If it is accepted that the gas injection unit and part are analogous to a convergent nozzle and pressure vessel system, a choked flow condition exists when the ratio of the pressure on the supply side of the nozzle and on the part side of the nozzle exceeds 0.
The material is written by experts in their specific fields and will include chapters on the following topics: Multiphase flow, Bubble columns, Sparged stirred vessels, Macroscale modelling, Microscale modelling, Runaway conditions, Behaviour of vessel contents, Choked flow, Measurement techniques.
A thermocouple measures temperature for fluid density correction and vapor pressure to predict choked flow.

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