Moist Air Domain

To view the complete domain source file, at the MATLAB^® Command prompt, type:

open([matlabroot '/toolbox/physmod/simscape/library/m/+foundation/+moist_air/moist_air.ssc'])

Abbreviated moist air domain declaration is shown below, with intermediate lookup table values omitted for readability.

domain moist_air
% Moist Air Domain

% Copyright 2017-2024 The MathWorks, Inc.

parameters
    trace_gas_model = foundation.enum.trace_gas_model.none; % Trace gas model
    %                                                         1 - none
    %                                                         2 - track_fraction
    %                                                         3 - track_properties

    enable_droplets = false; % Enable entrained water droplets

    R_a = {287.047, 'J/(kg*K)'}; % Dry air specific gas constant
    R_w = {461.523, 'J/(kg*K)'}; % Water vapor specific gas constant
    R_g = {188.923, 'J/(kg*K)'}; % Trace gas specific gas constant

    T_TLU = {[-56.55, -50:10:-10, -5:1:5, 10:10:350]', 'degC'}; % Temperature vector

    log_p_ws_TLU = {[
    0.537480914463379
    1.37059832527040
    ...
    16.4965784809407
    16.6206520873803], '1'}; % Log of water vapor saturation pressure vector in Pa

    h_w_vap_TLU = {[
    2836.88241275372
    2837.81392500514
    ...
    1027.31658328826
    892.746804215825], 'kJ/kg'}; % Water specific enthalpy of vaporization vector

    h_a_TLU = {[
    -56.8706902211881
    -50.2813451006832
    ...
    347.969511655333
    358.523684329954], 'kJ/kg'}; % Dry air specific enthalpy vector

    h_w_TLU = {[
    -104.361831315495
    -92.2353975846513
    ...
    654.537820276137
    674.908986576967], 'kJ/kg'}; % Water vapor specific enthalpy vector

    h_g_TLU = {[
    -56.8706902211881
    -50.2813451006832
    ...
    347.969511655333
    358.523684329954], 'kJ/kg'}; % Trace gas specific enthalpy vector

    mu_a_TLU = {[
    14.2568884161326
    14.6140128551699
    ...
    31.2307628665438
    31.5791070323335], 'uPa*s'}; % Dry air dynamic viscosity vector

    mu_w_TLU = {[
    6.98864148577410
    7.21462000349698
    ...
    21.9693374358760
    22.3836713303269], 'uPa*s'}; % Water vapor dynamic viscosity vector

    mu_g_TLU = {[
    14.2568884161326
    14.6140128551699
    ...
    31.2307628665438
    31.5791070323335], 'uPa*s'}; % Trace gas dynamic viscosity vector

    k_a_TLU = {[
    19.8808491891482
    20.4162457047568
    ...
    46.7832371087507
    47.3667074352967], 'mW/(m*K)'}; % Dry air thermal conductivity vector

    k_w_TLU = {[
    12.4916816538045
    12.9847788176262
    ...
    47.8689040929333
    48.9770898119082], 'mW/(m*K)'}; % Water vapor thermal conductivity vector

    k_g_TLU = {[
    19.8808491891482
    20.4162457047568
    ...
    46.7832371087507
    47.3667074352967], 'mW/(m*K)'}; % Trace gas thermal conductivity vector

    cp_a_TLU = {[
    1.00608854886677
    1.00592522838662
    ...
    1.05425061343244
    1.05658392149181], 'kJ/(kg*K)'}; % Dry air specific heat vector

    cp_w_TLU = {[
    1.85149054448685
    1.85123731225933
    ...
    2.03428214917861
    2.03995111098726], 'kJ/(kg*K)'}; % Water vapor specific heat vector

    cp_g_TLU = {[
    1.00608854886677
    1.00592522838662
    ...
    1.05425061343244
    1.05658392149181], 'kJ/(kg*K)'}; % Trace gas specific heat vector

    cp_d_TLU = {[
    1.85149054448685
    1.85123731225933
    ...
    2.03428214917861
    2.03995111098726], 'kJ/(kg*K)'}; % Liquid water specific heat vector

    Pr_a_TLU = {[
    0.721482872359986
    0.720044440666024
    ...
    0.703778809351741
    0.704418325698712], '1'}; % Dry air Prandtl number pressure vector

    Pr_w_TLU = {[
    1.03584160950647
    1.02858692718863
    ...
    0.933629708512201
    0.932305193584043], '1'}; % Water vapor Prandtl number pressure vector

    Pr_g_TLU = {[
    0.721482872359986
    0.720044440666024
    ...
    0.703778809351741
    0.704418325698712], '1'}; % Trace gas Prandtl number pressure vector

    int_dh_T_a_TLU = {[
    0
    0.0299708128724171
    ...
    1.05825606477651
    1.07533024233389], 'kJ/(kg*K)'}; % Dry air integral of dh/T vector

    int_dh_T_w_TLU = {[
    0
    0.0551555684988988
    ...
    1.96803192003337
    2.00098769223782], 'kJ/(kg*K)'}; % Water vapor integral of dh/T vector

    int_dh_T_g_TLU = {[
    0
    0.0299708128724171
    ...
    1.05825606477651
    1.07533024233389], 'kJ/(kg*K)'}; % Trace gas integral of dh/T vector

    int_dh_T_d_TLU = {[
    0
    0.0551555684988988
    ...
    1.96803192003337
    2.00098769223782], 'kJ/(kg*K)'}; % Liquid water integral of dh/T vector

    D_w = {25, 'mm^2/s'}; % Water vapor diffusivity in air
    D_g = {1,  'mm^2/s'}; % Trace gas diffusivity in air

    p_min = {1,      'kPa' }; % Minimum valid pressure
    p_max = {inf,    'MPa' }; % Maximum valid pressure
    T_min = {-56.55, 'degC'}; % Minimum valid temperature
    T_max = {350,    'degC'}; % Maximum valid temperature
    properties_range_check = simscape.enum.assert.action.error; % Pressure and temperature outside valid range
    %                                                             0 - none
    %                                                             1 - warn
    %                                                             2 - error

    h_a_ref     = {399.284757014822, 'kJ/kg'}; % Dry air specific enthalpy at reference temperature
    h_w_ref     = {2500.89261781717, 'kJ/kg'}; % Water vapor specific enthalpy at reference temperature
    h_g_ref     = {399.284757014822, 'kJ/kg'}; % Trace gas specific enthalpy at reference temperature
    h_w_vap_ref = {2500.93420564316, 'kJ/kg'}; % Water specific enthalpy of vaporization at reference temperature

    p_atm = {0.101325, 'MPa' }; % Atmospheric pressure
    T_atm = {20,       'degC'}; % Atmospheric temperature

    rho_a_atm = {1.20412924943656, 'kg/m^3'   }; % Dry air density at reference condition
    cp_a_atm  = {1.00615115677232, 'kJ/(kg*K)'}; % Dry air specific heat at reference condition
    k_a_atm   = {25.8738284673185, 'mW/(m*K)' }; % Dry air thermal conductivity at reference condition
end

variables
    p   = {0.1, 'MPa'}; % Pressure
    T   = {300, 'K'  }; % Temperature
    x_w = {0,   '1'  }; % Specific humidity
    x_g = {0,   '1'  }; % Trace gas mass fraction
    r_d = {0,   '1'  }; % Mass ratio of water droplets to moist air
end

variables (Balancing = true)
    mdot   = {0, 'kg/s'}; % Mass flow rate
    Phi    = {0, 'kW'  }; % Energy flow rate
    mdot_w = {0, 'kg/s'}; % Water vapor mass flow rate
    mdot_g = {0, 'kg/s'}; % Trace gas mass flow rate
    mdot_d = {0, 'kg/s'}; % Water droplets mass flow rate
end

end

The domain declaration contains the following variables and parameters:

Across variable p (absolute pressure), in MPa
Through variable mdot (mixture mass flow rate), in kg/s
Across variable T (temperature), in K
Through variable Phi (mixture energy flow rate), in kW
Across variable x_w (specific humidity), unitless
Through variable mdot_w (water vapor mass flow rate), in kg/s
Across variable x_g (trace gas mass fraction), unitless
Through variable mdot_g (trace gas mass flow rate), in kg/s
Across variable r_d (mass ratio of water droplets to moist air), unitless
Through variable mdot_d (water droplets mass flow rate), in kg/s
Parameter p_min, defining the minimum allowable pressure
Parameter p_max, defining the maximum allowable pressure
Parameter T_min, defining the minimum allowable temperature
Parameter T_max, defining the maximum allowable temperature
Parameter p_atm, defining the atmospheric pressure
Parameter T_atm, defining the atmospheric temperature

Parameter trace_gas_model provides a choice of three trace gas models:

foundation.enum.trace_gas_model.none — None
foundation.enum.trace_gas_model.track_fraction — Track mass fraction only
foundation.enum.trace_gas_model.track_properties — Track mass fraction and gas properties

Parameter enable_droplets provides an option to model water droplets suspended in the moist air flow.

In the Foundation Moist Air library, the Moist Air Properties (MA) block serves as the source for domain parameter values, including the selection of the trace gas model and enabling the water droplet tracking. For more information on propagation of domain parameters, see Working with Domain Parameters.

The moist air mixture is composed of three gas species. The default domain parameter values correspond to dry air, water vapor, and carbon dioxide:

R_a = {287.047, 'J/(kg*K)'}; % Dry air specific gas constant
R_w = {461.523, 'J/(kg*K)'}; % Water vapor specific gas constant
R_g = {188.923, 'J/(kg*K)'}; % Trace gas specific gas constant

You can modify these parameter values in the Moist Air Properties (MA) block to model any three-species gas mixture.

The domain declaration also contains sets of parameters that define various dry air, water vapor, and trace gas properties in the form of lookup table data. The table lookup is with respect to the temperature vector, T_TLU. These parameter declarations propagate to the components connected to the Moist Air domain, and therefore you can use them in the tablelookup function in the component equations.

To refer to this domain in your custom component declarations, use the following syntax:

foundation.moist_air.moist_air

Moist Air Domain

See Also

Topics