Yunus A. Çengel,
University of Nevada, Reno
Michael A. Boles,
North Carolina State University
| Back pressure | is the pressure applied at the nozzle discharge region.
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| Bernoulli's equation | is a form of the conservation of momentum principle for steady-flow control volumes.
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| Converging-diverging nozzles | are ducts in which the flow area first decreases and then increases in the direction of the flow.
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| Critical properties | are the properties of a fluid at a location where the Mach number is unity.
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| Critical ratios | are the ratios of the stagnation to static properties when the Mach number is unity.
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| Diffuser efficiency | is a measure of a diffuser's ability to increase the pressure of the fluid. It is expressed in terms of the ratio of the kinetic energy that can be converted to pressure rise if the fluid is discharged at the actual exit stagnation pressure to the maximum kinetic energy available for converting to pressure rise. These two quantities are identical for an isentropic diffuser since the actual exit stagnation pressure in this case becomes equal to the inlet stagnation pressure, yielding an efficiency of 100 percent.
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| Discharge coefficient | a parameter that is used to express the performance of a nozzle, is defined as the ratio of the mass flow rate through the nozzle to the mass flow rate through the nozzle for isentropic flow from the same inlet state to the same exit pressure.
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| Dynamic temperature | is the kinetic energy per unit mass divided by the constant pressure specific heat and corresponds to the temperature rise during the stagnation process.
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| Fanno line | is the locus of all states for frictionless adiabatic flow in a constant-area duct plotted on a T-s diagram.
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| Hypersonic flow | occurs when a flow has a Mach number M >>1.
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| Isentropic stagnation state | is the stagnation state when the stagnation process is reversible as well as adiabatic (i.e., isentropic). The entropy of a fluid remains constant during an isentropic stagnation process.
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| Mach number | named after the Austrian physicist Ernst Mach (1838-1916), is the ratio of the actual velocity of the fluid (or an object in still air) to the velocity of sound in the same fluid at the same state.
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| Normal shock wave | is an abrupt change over a very thin section normal to the direction of flow in which the flow transitions from supersonic to subsonic flow. This abrupt change in the flow causes a sudden drop in velocity to subsonic levels and a sudden increase in pressure. Flow through the shock is highly irreversible, and thus it cannot be approximated as isentropic.
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| Pressure recovery factor | a measure of a diffuser's ability to increase the pressure of the fluid, is expressed in terms of the ratio of the actual stagnation pressure of a fluid at the diffuser exit relative to the maximum possible stagnation pressure.
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| Pressure rise coefficient | a measure of a diffuser's ability to increase the pressure of the fluid, is defined as the ratio of the actual pressure rise in the diffuser to the pressure rise that would be realized if the process were isentropic.
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| Rayleigh line | is the locus of all states for frictionless flow in a constant-area duct with heat transfer plotted on a T-s diagram.
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| Sonic flow | occurs when a flow has a Mach number M =1.
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| Stagnation enthalpy | represents the total energy of a flowing fluid stream per unit mass and represents the enthalpy of a fluid when it is brought to rest adiabatically with no work. The stagnation enthalpy equals the static enthalpy when the kinetic energy of the fluid is negligible.
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| Stagnation pressure | is the pressure a fluid attains when brought to rest isentropically. For ideal gases with constant specific heats, the stagnation pressure is related to the static pressure of the fluid through the isentropic process equation relating pressure and temperature.
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| Stagnation properties | are the properties of a fluid at the stagnation state. These properties are called stagnation temperature, stagnation pressure, stagnation density, etc. The stagnation state and the stagnation properties are indicated by the subscript 0.
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| Stagnation (or total) temperature | is the temperature an ideal gas will attain when it is brought to rest adiabatically.
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| Subsonic flow | occurs when a flow has a Mach number M <1.
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| Supersaturated steam | is steam that exists in the wet region without containing any liquid. This phenomenon would exist due to the supersaturation process.
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| Supersaturation | is the phenomenon owing to steam flowing through a nozzle with the high velocities and exiting the nozzle in the saturated region. Since the residence time of the steam in the nozzle is small, and there may not be sufficient time for the necessary heat transfer and the formation of liquid droplets, the condensation of the steam may be delayed for a little while.
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| Supersonic flow | occurs when a flow has a Mach number M >1.
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| Throat | of a converging-diverging nozzle is located at smallest flow area.
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| Transsonic flow | occurs when a flow has a Mach number M @1.
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| Velocity coefficient | a parameter that is used to express the performance of a nozzle, is defined as the ratio of the actual velocity at nozzle exit to the velocity at nozzle exit for isentropic flow from the same inlet state to the same exit pressure.
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| Velocity of sound | (or the sonic velocity) is the velocity at which an infinitesimally small pressure wave travels through a medium.
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| Wilson line | is the locus of points where condensation will take place regardless of the initial temperature and pressure as steam flows through a high-velocity nozzle. The Wilson line is often approximated by the 4 percent moisture line on the h-s diagram for steam. Therefore, steam flowing through a high-velocity nozzle is assumed to begin condensation when the 4 percent moisture line is crossed.
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| Choked flow | occurs in a nozzle when the mass flow reaches a maximum value for the minimum flow area. This happens when the flow properties are those required to increase the fluid velocity to the velocity of sound at the minimum flow area location.
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2002 McGraw-Hill Higher Education