Air Volume
Control volume element of Air
Description
Equations
Variables
Connections
Parameters
See Also
The Air Volume component models a generic control volume for the lumped thermal fluid simulation of Air. This component calculates mainly the mass and energy conservation.
The calculation is changed based on parameter values of Fidelity of properties and Dynamics of mass in the Air Settings component.
Fidelity of properties = Constant and Dynamics of mass = Static
If Type of Branch is a⇒b+c+d (Branching), Mass conservation is calculated with:
NumOfRoute=∑x=b,c,d{1.0port__x on=true0.0port__x on=false
`port_x.mflow`=−1NumOfRoute⋅`port_a.mflow` if port__x on=true x=b,c,d
`port_a.p`=p
`port_x.p`=p if port__x on=true x=b,c,d
If Type of Branch is a+c+d⇒b (Confluence), Mass conservation is calculated with:
NumOfRoute=1.0+∑x=c,d{1.0port__x on=true0.0port__x on=false
`port_b.mflow`=−(`port_a.mflow`+∑x=c,d{`port_x.mflow`port__x on=true0.0port__x on=false)
p=−1NumOfRoute⋅∑x=a,c,d{`port_x.p`port__x on=true0.0port__x on=false
`port_b.p`=p
Energy conservation is calculated with:
c__p⋅M⋅ⅆTⅆ t=`port_a.mflow`⋅ActualStream`port_a.hflow` +∑x=b,c,d{`port_x.mflow`⋅ActualStream`port_x.hflow`port__x on=true0.0port__x on=false+{`heat.Q_flow`useHeatPort=true0.0useHeatPort=false
State equation:
p=ρ⋅R__gas⋅T
Relationship of mass:
u=UM
M=ρ⋅V
Definition of Enthalpy:
hflow=Function__hflowT
u=hflow−pρ
Port definitions:
`port_a.hflow`=hflow
`port_x.hflow`=hflow if port__x on=true x=b,c,d
`port_a.rho`=ρ
`port_x.rho`=ρ if port__x on=true x=b,c,d
`port_a.T`=T
`port_x.T`=T if port__x on=true x=b,c,d
v1=`port_a.mflow`ActualStream`port_a.rho`⋅A1
vi=`port_x.mflow`ActualStream`port_x.rho`⋅Ai if port__x on=true x=b,c,d,the order of vector is b=2,c=3,d=4
`heat.T`=T
(*) Regarding the value of properties, see more details in Air Settings.
Fidelity of properties = Constant and Dynamics of mass = Dynamic
Mass conservation is calculated with:
ⅆρⅆ t=`port_a.mflow`+∑x=b,c,d{`port_x.mflow`port__x on=true0.0port__x on=falseV
ⅆUⅆ t=`port_a.mflow`⋅ActualStream`port_a.hflow` +∑x=b,c,d{`port_x.mflow`⋅ActualStream`port_x.hflow`port__x on=true0.0port__x on=false+{`heat.Q_flow`useHeatPort=true0.0useHeatPort=false
c__p−R__gas⋅ⅆTⅆ t=ⅆUⅆ tρ⋅V−U⋅ρ2⋅V
(*) Regarding the values and equations of properties, see more details in Air Settings.
Fidelity of properties: Ideal Gas (NASA Polynomial) and Dynamics of mass = Static
Function__cpT⋅M⋅ⅆTⅆ t=`port_a.mflow`⋅ActualStream`port_a.hflow` +∑x=b,c,d{`port_x.mflow`⋅ActualStream`port_x.hflow`port__x on=true0.0port__x on=false+{`heat.Q_flow`useHeatPort=true0.0useHeatPort=false
(*) The properties are defined with NASA polynomials and coefficients. For details, see Air Settings.
Fidelity of properties: Ideal Gas (NASA Polynomial) and Dynamics of mass = Dynamic
Function__cpT−R__gas⋅ⅆTⅆ t=ⅆUⅆ tρ⋅V−U⋅ρ2⋅V
Symbol
Units
Modelica ID
p
Pa
Pressure
T
K
Temperature
ρ
kgm3
Density
rho
hflow
Jkg
Specific enthalpy
u
Specific energy
U
J
Energy
M
kg
Mass
mflow
kgs
Mass flow rate
NumOfRoute
−
Number of valid routes
v
ms
Velocity of flow
Name
Condition
port__a
Air Port
port_a
port__b
if port_c on is true.
port_b
port__c
if port_d on is true.
port_c
port__d
if port_b on is true.
port_d
states
if Internal states output is true.
Internal states output. The breakdown list of output variables in states are the followings:
[1] : Pressure [2] : Temperature
[3] : Density [4] : Specific enthalpy
[5] : Velocity of port_a
[6] : Velocity of port_b
[7] : Velocity of port_c
[8] : Velocity of port_d
heat
if Heat port is true.
Heat Port
Default
Airsimulationsettings
AirSettings1
Specify a component of Air simulation settings
Settings
V
0.001
m3
Volume of the node
A
Pi400,Pi400,Pi400,Pi400
m2
Flow area of each port
1 : port_a, 2 : port_b
3 : port_c, 4 : port_d
port__b on
false
If true, port_b is valid
sw_b
port__c on
If true, port_c is valid
sw_c
port__d on
If true, port_d is valid
sw_d
p__start
101325
Initial condition of Pressure
p_start
T__start
293.15
Initial condition of temperature
T_start
Internalstatesoutput
If true, the output of the internal states is valid. The breakdown list of output variables in states are the followings:
[5] : Velocity of port_a [6] : Velocity of port_b
[7] : Velocity of port_c [8] : Velocity of port_d
useStates
Heat port
If true, Heat port is valid
useHeatPort
Type ofBranch
a⇒b+c+d
Branch type setting only for Static mass flow simulation, when Dynamics of mass option of Air Setting is Static.
a⇒b+c+d :
The input flow is split into 3 ports
a+c+d⇒b
The input flows from 3 ports are confluent
TypeOfBranch
Heat Transfer Library Overview
Air Overview
Air Basic Overview
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