Moisture Separator (MA)

Remove water vapor and water droplets from moist air flow

Since R2024b

Libraries:
Simscape / Foundation Library / Moist Air / Elements

Description

The Moisture Separator (MA) block removes a specified fraction of water vapor and water droplets from the flow through the block in a moist air network. The block assumes that method that removes the moisture is mechanical, and that the temperature change of the flow is negligible across the ports.

If the Nominal density parameter, ρ_nom, is greater than zero, then the pressure drop is

$p_{A} - p_{B} = K_{1} {\dot{m}}_{A} \sqrt{{\dot{m}}_{A}^{2} + {(f_{l a m} {\dot{m}}_{n o m})}^{2}} \frac{R T_{i n}}{p_{i n}}$

where:

ṁ_A is the mass flow rate at port A.
ṁ_nom is the value of the Nominal mass flow rate parameter.
f_lam is the fraction of the nominal mixture mass flow rate for the laminar flow transition.
p_in is the inlet pressure, p_A or p_B, depending on flow direction.
T_in is the inlet temperature, T_A or T_B, depending on flow direction.
R is the specific gas constant.

The proportionality constant, K₁, is

$K_{1} = \frac{Δ p_{n o m} ρ_{n o m}}{{\dot{m}}_{n o m}^{2}}$

where ρ_nom is the value of the Nominal density parameter and Δp_nom is the value of the Nominal pressure drop parameter.

If the Nominal density parameter is zero, then the pressure drop is

$p_{A} - p_{B} = K_{2} {\dot{m}}_{A} \sqrt{{\dot{m}}_{A}^{2} + {(f_{l a m} {\dot{m}}_{n o m})}^{2}}$

where the proportionality constant, K₁, is

$K_{2} = \frac{Δ p_{n o m}}{{\dot{m}}_{n o m}^{2}}$

Because the block assumes the flow resistance is adiabatic, the mixture specific total enthalpies are equal,

$h_{A} + \frac{1}{2} {(\frac{{\dot{m}}_{A} R T_{A}}{S p_{A}})}^{2} = h_{B} + \frac{1}{2} {(\frac{{\dot{m}}_{B} R T_{B}}{S p_{B}})}^{2}$

where:

h_A and h_B are the specific enthalpies at ports A and B, respectively.
S is the value of the Cross-sectional area at ports A and B parameter.

Mass and Energy Balance

The mass balance equations for the moist air, water vapor, trace gas, and water droplets are

$\begin{array}{l} {\dot{m}}_{A} + {\dot{m}}_{B} - {\dot{m}}_{w, r e m o v e d} = 0 \\ {\dot{m}}_{w A} + {\dot{m}}_{w B} - {\dot{m}}_{w, r e m o v e d} = 0 \\ {\dot{m}}_{g A} + {\dot{m}}_{g B} = 0 \\ {\dot{m}}_{d A} + {\dot{m}}_{d B} - {\dot{m}}_{d, r e m o v e d} = 0 \end{array}$

where:

ṁ_wA and ṁ_wB are the water vapor mass flow rates at ports A and B, respectively.
ṁ_gA and ṁ_gB are the trace gas mass flow rates at ports A and B, respectively.
ṁ_dA and ṁ_dB are the water droplets mass flow rates at ports A and B, respectively.

The water vapor removal rate is

${\dot{m}}_{w, r e m o v e d} = θ_{w} {\dot{m}}_{M A, i n} x_{w, i n},$

where:

θ_w is the value of the Fraction of water vapor removed parameter.
ṁ_MA,in is the moist air mass flow rate of the inflow port, which can be either port A or B.
x_w,in is the water vapor mass fraction at the inflow port, which can be either port A or B.

The water droplet removal rate is

${\dot{m}}_{d, r e m o v e d} = θ_{d} {\dot{m}}_{M A, i n} r_{d, i n},$

where:

θ_d is the value of the Fraction of water droplets removed parameter.
r_d,in is the mass ratio of water droplets to moist air at the inflow port, which can be either port A or B.

The energy balance equation is

$Φ_{A} + Φ_{B} - Φ_{r e m o v e d} = 0,$

where Φ_A and Φ_B are the energy flow rates through ports A and B, respectively.

Φ_removed is the energy flow rate from the removed water vapor and water droplets. This term does not represent heat or work and only includes the specific enthalpy contributions from the removed the water vapor and water droplets,

$Φ_{r e m o v e d} = {\dot{m}}_{w, r e m o v e d} h_{w, i n} + {\dot{m}}_{d, r e m o v e d} h_{d, i n},$

where h_w,in and h_d,in are the water vapor and water droplet specific enthalpies at the inflow port.

Assumptions and Limitations

The block does not model any physics or thermodynamic effects related to removing water vapor and water droplets.

Ports

Output

expand all

W — Rate of water vapor removed, kg/s
physical signal

Physical signal that outputs the rate of water vapor removed, in kg/s.

D — Rate of water droplets removed, kg/s
physical signal

Physical signal that outputs the rate of water droplets removed, in kg/s.

Conserving

expand all

A — Inlet or outlet
moist air

Moist air conserving port associated with the inlet or outlet of the moisture separator. This block has no intrinsic directionality.

B — Inlet or outlet
moist air

Moist air conserving port associated with the inlet or outlet of the moisture separator. This block has no intrinsic directionality.

Parameters

expand all

Fraction of water vapor removed — Water vapor removal fraction
`0.5` (default) | scalar in the range of [0,1]

Fraction of water vapor removed from the moist air flow through the block.

Removed water vapor condensed to liquid — Whether to condense removed water vapor
`off` (default) | `on`

Option to condense the removed water vapor to liquid. When you select this check box, the block converts water vapor to liquid before removing it, which means that the latent heat of the water vapor remains in the flow. In this case, the temperature change across the block may be more significant.

Fraction of water droplets removed — Water droplet removal fraction
`0.5` (default) | scalar in the range of [0,1]

Fraction of water droplets removed from the moist air flow through the block.

Nominal pressure drop — Pressure drop at nominal operating conditions
`0.001 MPa` (default) | scalar

Pressure drop from the inlet to outlet at nominal operating conditions. The block uses the nominal parameters to calculate the constant of proportionality between the pressure drop and the mass flow rate.

Nominal mass flow rate — Mass flow rate at nominal operating conditions
`0.1 kg/s` (default) | positive scalar

Mass flow rate of the air mixture through the block at nominal operating conditions. The block uses the nominal parameters to calculate the constant of proportionality between the pressure drop and the mass flow rate.

Nominal density — Density at nominal operating conditions
`0 kg/m^3` (default) | positive scalar

Mass density of the moist air mixture inside the flow resistance at nominal operating conditions. The block uses the nominal parameters to calculate the constant of proportionality between the pressure drop and the mass flow rate. Set this parameter to zero to ignore the dependence of the pressure drop on the air mixture density.

Cross-sectional area at ports A and B — Flow area at ports
`0.01 m^2` (default) | positive scalar

Flow area at the ports of the separator. The block assumes that the ports are identical in size.

Fraction of nominal mixture mass flow rate for laminar flow transition — Ratio of threshold to nominal mass flow rates
`1e-3` (default) | positive scalar

Ratio of the threshold mass flow rate to the nominal mass flow rate of the air mixture. The block uses this parameter to set the threshold for the linearization of the pressure drop.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2024b

Moisture Separator (MA)

Description

Mass and Energy Balance

Assumptions and Limitations

Ports

Output

W — Rate of water vapor removed, kg/s
physical signal

D — Rate of water droplets removed, kg/s
physical signal

Conserving

A — Inlet or outlet
moist air

B — Inlet or outlet
moist air

Parameters

Fraction of water vapor removed — Water vapor removal fraction
`0.5` (default) | scalar in the range of [0,1]

Removed water vapor condensed to liquid — Whether to condense removed water vapor
`off` (default) | `on`

Fraction of water droplets removed — Water droplet removal fraction
`0.5` (default) | scalar in the range of [0,1]

Nominal pressure drop — Pressure drop at nominal operating conditions
`0.001 MPa` (default) | scalar

Nominal mass flow rate — Mass flow rate at nominal operating conditions
`0.1 kg/s` (default) | positive scalar

Nominal density — Density at nominal operating conditions
`0 kg/m^3` (default) | positive scalar

Cross-sectional area at ports A and B — Flow area at ports
`0.01 m^2` (default) | positive scalar

Fraction of nominal mixture mass flow rate for laminar flow transition — Ratio of threshold to nominal mass flow rates
`1e-3` (default) | positive scalar

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

See Also

Topics

Moisture Separator (MA)

Description

Mass and Energy Balance

Assumptions and Limitations

Ports

Output

W — Rate of water vapor removed, kg/s physical signal

D — Rate of water droplets removed, kg/s physical signal

Conserving

A — Inlet or outlet moist air

B — Inlet or outlet moist air

Parameters

Fraction of water vapor removed — Water vapor removal fraction 0.5 (default) | scalar in the range of [0,1]

Removed water vapor condensed to liquid — Whether to condense removed water vapor off (default) | on

Fraction of water droplets removed — Water droplet removal fraction 0.5 (default) | scalar in the range of [0,1]

Nominal pressure drop — Pressure drop at nominal operating conditions 0.001 MPa (default) | scalar

Nominal mass flow rate — Mass flow rate at nominal operating conditions 0.1 kg/s (default) | positive scalar

Nominal density — Density at nominal operating conditions 0 kg/m^3 (default) | positive scalar

Cross-sectional area at ports A and B — Flow area at ports 0.01 m^2 (default) | positive scalar

Fraction of nominal mixture mass flow rate for laminar flow transition — Ratio of threshold to nominal mass flow rates 1e-3 (default) | positive scalar

Extended Capabilities

C/C++ Code Generation Generate C and C++ code using Simulink® Coder™.

Version History

See Also

Topics

W — Rate of water vapor removed, kg/s
physical signal

D — Rate of water droplets removed, kg/s
physical signal

A — Inlet or outlet
moist air

B — Inlet or outlet
moist air

Fraction of water vapor removed — Water vapor removal fraction
`0.5` (default) | scalar in the range of [0,1]

Removed water vapor condensed to liquid — Whether to condense removed water vapor
`off` (default) | `on`

Fraction of water droplets removed — Water droplet removal fraction
`0.5` (default) | scalar in the range of [0,1]

Nominal pressure drop — Pressure drop at nominal operating conditions
`0.001 MPa` (default) | scalar

Nominal mass flow rate — Mass flow rate at nominal operating conditions
`0.1 kg/s` (default) | positive scalar

Nominal density — Density at nominal operating conditions
`0 kg/m^3` (default) | positive scalar

Cross-sectional area at ports A and B — Flow area at ports
`0.01 m^2` (default) | positive scalar

Fraction of nominal mixture mass flow rate for laminar flow transition — Ratio of threshold to nominal mass flow rates
`1e-3` (default) | positive scalar

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.