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Mass Flow Rate

Mass Flow Rate. Flow rate out of a tank depends on tank temperature, pressure and size of throat. M. 1. Mass Flow Rate. For a Diatomic Gas (e.g.,Air): Mass flow/unit area. M. 1. Mach #-Area Relation. Values of A/A* tabulated over a range of Mach #s). Two values for M at A

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Mass Flow Rate

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  1. Mass Flow Rate Flow rate out of a tank depends on tank temperature, pressure and size of throat. M 1

  2. Mass Flow Rate For a Diatomic Gas (e.g.,Air): Mass flow/unit area M 1

  3. Mach #-Area Relation Values of A/A* tabulated over a range of Mach #s) Two values for M at A One subsonic, One supersonic. Solution depends on p. M=1 A* A

  4. Mach #-Area Relation • If the M = 1 at throat the flow is chocked. • For each value of A/A* there are two solutions, one subsonic, the other supersonic. • If M=1 at the smallest cross-sectional area the mass flow rate is largest. • If M < 1 at minimum area (A > A*), pretend. • If A reduced below A*, decreases.

  5. Converging Nozzle Flow • Steady, adiabatic, reversible, no work flow • If backpressure pB = patm: no flow • As pB is lowered: flow • Assume here pB = pe • Eventually pB so low, (pe/p0=.528), Me = 1 • Nozzle chocked; lowering pB no longer changes conditions in nozzle (message of lower pB cannot pass through sonic throat). Here pB no longer equal pe (see later) Pe Me p0=patm pB

  6. Converging Nozzle Flow • If nozzle chocked, flow rate fixed for given upstream stagnation pressure and temperature. • Use as flow-meter (chocked orifice meter). • Assumed flow from atmosphere to partially evacuated vessel; similar from pressurized vessel to atmosphere or lower pressure vessel

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