Controlled Mass Flow Rate Source (MA)

Generate time-varying mass flow rate

• Library:
• Simscape / Foundation Library / Moist Air / Sources

• Description

The Controlled Mass Flow Rate Source (MA) block represents an ideal mechanical energy source in a moist air 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 moist air to flow from port A to port B.

The equations describing the source use these symbols.

 cp Specific heat at constant pressure h Specific enthalpy ht Specific total enthalpy $\stackrel{˙}{m}$ Mass flow rate (flow rate associated with a port is positive when it flows into the block) p Pressure ρ Density R Specific gas constant s Specific entropy T Temperature Φwork Power delivered to the moist air flow through the source

Subscripts A and B indicate the appropriate port.

Mass balance:

$\begin{array}{l}{\stackrel{˙}{m}}_{A}+{\stackrel{˙}{m}}_{B}=0\\ {\stackrel{˙}{m}}_{wA}+{\stackrel{˙}{m}}_{wB}=0\\ {\stackrel{˙}{m}}_{gA}+{\stackrel{˙}{m}}_{gB}=0\end{array}$

Energy balance:

${\Phi }_{A}+{\Phi }_{B}+{\Phi }_{work}=0$

If the source performs no work (Power added parameter is set to None), then ${\Phi }_{work}=0$.

If the source is isentropic (Power added parameter is set to Isentropic power), then

${\Phi }_{work}={\stackrel{˙}{m}}_{A}\left({h}_{tB}-{h}_{tA}\right)$

where

$\begin{array}{l}{h}_{tA}={h}_{A}+\frac{1}{2}{\left(\frac{{\stackrel{˙}{m}}_{A}}{{\rho }_{A}{S}_{A}}\right)}^{2}\\ {h}_{tB}={h}_{B}+\frac{1}{2}{\left(\frac{{\stackrel{˙}{m}}_{B}}{{\rho }_{B}{S}_{B}}\right)}^{2}\end{array}$

The mixture-specific enthalpies, hA = h(TA) and hB = h(TB), are constrained by the isentropic relation, that is, there is no change in entropy:

${\int }_{{T}_{A}}^{{T}_{B}}\frac{1}{T}dh\left(T\right)=R\mathrm{ln}\left(\frac{{p}_{B}}{{p}_{A}}\right)$

The quantity specified by the input signal of the source is

${\stackrel{˙}{m}}_{A}={\stackrel{˙}{m}}_{specified}$

Assumptions and Limitations

• There are no irreversible losses.

• There is no heat exchange with the environment.

Ports

Input

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

Conserving

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Moist air conserving port. A positive mass flow rate causes moist air to flow from port A to port B

Moist air conserving port. A positive mass flow rate causes moist air to flow from port A to port B.

Parameters

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Select whether the source performs work on the moist air flow:

• Isentropic power — The source performs isentropic work on the moist air 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.