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Controlled Mass Flow Rate Source (G)

Generate time-varying mass flow rate

  • Library:
  • Simscape / Foundation Library / Gas / Sources

Description

The Mass Flow Rate Source (G) block represents an ideal mechanical energy source in a gas network. The mass flow rate is controlled by the input physical signal at port M. The source can maintain the specified mass flow rate regardless of the pressure differential. There is no flow resistance and no heat exchange with the environment. A positive mass flow rate causes gas to flow from port A to port B.

You can choose whether the source performs work on the gas flow:

  • If the source is isentropic (Power added parameter is set to Isentropic power), then the isentropic relation depends on the gas property model.

    Gas ModelEquations
    Perfect gas(pA)ZR/cpTA=(pB)ZR/cpTB
    Semiperfect gas0TAcp(T)TdTZRln(pA)=0TBcp(T)TdTZRln(pB)
    Real gass(TA,pA)=s(TB,pB)

    The power delivered to the gas flow is based on the specific total enthalpy associated with the isentropic process.

    Φwork=m˙A(hA+wA22)m˙B(hB+wB22)

  • If the source performs no work (Power added parameter is set to None), then the defining equation states that the specific total enthalpy is equal on both sides of the source. It is the same for all three gas property models.

    hA+wA22=hB+wB22

    The power delivered to the gas flow Φwork = 0.

The equations use these symbols:

cpSpecific heat at constant pressure
hSpecific enthalpy
m˙Mass flow rate (flow rate associated with a port is positive when it flows into the block)
pPressure
RSpecific gas constant
sSpecific entropy
TTemperature
wFlow velocity
ZCompressibility factor
ΦworkPower delivered to the gas flow through the source

Subscripts A and B indicate the appropriate port.

Variables

Use the Variables tab in the block dialog box (or the Variables section in the block Property Inspector) to set the priority and initial target values for the block variables prior to simulation. For more information, see Set Priority and Initial Target for Block Variables and Initial Conditions for Blocks with Finite Gas Volume.

Assumptions and Limitations

  • There are no irreversible losses, nor heat exchange with the environment.

Ports

Input

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Input physical signal that specifies the mass flow rate of the gas through the source.

Conserving

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Gas conserving port. A positive mass flow rate causes gas to flow from port A to port B.

Gas conserving port. A positive mass flow rate causes gas to flow from port A to port B.

Parameters

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Select whether the source performs work on the gas flow:

  • Isentropic power — The source performs isentropic work on the gas to maintain the specified mass flow rate, regardless of the pressure differential. Use this option to represent an idealized pump or compressor and properly account for the energy input and output, especially in closed-loop systems.

  • None — The source performs no work on the flow, neither adding nor removing power, regardless of the mass flow rate produced by the source. Use this option to set up the desired flow condition upstream of the system, without affecting the temperature of the flow.

Area normal to flow path at port A.

Area normal to flow path at port B.

Introduced in R2016b

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