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 The MathWorks, Inc.

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

    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 = [
        0.537480914463376
        1.37059832527040
        ...
        16.4965444877527
        16.6206369090880]; % Log of water vapor saturation pressure vector in Pa

    h_w_vap_TLU = {[
        2836.88241275372
        2837.81392500514
        ...
        1027.62017777647
        892.733785613825], 'kJ/kg'}; % Water specific enthalpy of vaporization vector

    h_a_TLU = {[
        342.416126230579
        349.005511058471
        ...
        747.258774447567
        757.813011774199], 'kJ/kg'}; % Dry air specific enthalpy vector

    h_w_TLU = {[
        2396.55944251649
        2408.68643343608
        ...
        3155.43043805905
        3175.80160435813], 'kJ/kg'}; % Water vapor specific enthalpy vector

    h_g_TLU = {[
        342.416126230579
        349.005511058471
        ...
        747.258774447567
        757.813011774199], 'kJ/kg'}; % Trace gas specific enthalpy vector

    mu_a_TLU = {[
        14.2568883320012
        14.6140127728333
        ...
        31.2307628592324
        31.5791070262086], 'uPa*s'}; % Dry air dynamic viscosity vector

    mu_w_TLU = {[
        6.81365662228272
        7.04953750742707
        ...
        21.1317199525111
        21.4937680016671], 'uPa*s'}; % Water vapor dynamic viscosity vector

    mu_g_TLU = {[
        14.2568883320012
        14.6140127728333
        ...
        31.2307628592324
        31.5791070262086], 'uPa*s'}; % Trace gas dynamic viscosity vector

    k_a_TLU = {[
        19.8808489374933
        20.4162454629695
        ...
        46.7832370779530
        47.3667074066625], 'mW/(m*K)'}; % Dry air thermal conductivity vector

    k_w_TLU = {[
        11.4628821597600
        11.9419974889350
        ...
        43.1675775109350
        44.0380174089350], 'mW/(m*K)'}; % Water vapor thermal conductivity vector

    k_g_TLU = {[
        19.8808489374933
        20.4162454629695
        ...
        46.7832370779530
        47.3667074066625], 'mW/(m*K)'}; % Trace gas thermal conductivity vector

    cp_a_coeff = {[
        1.02664779928781
        -0.000177515573577911
        3.66581785159269e-07], 'kJ/(kg*K)'}; % Dry air specific heat polynomial coefficients

    cp_w_coeff = {[
        1.47965047747103
        0.00120021143370507
        -3.86145131678391e-07], 'kJ/(kg*K)'}; % Water vapor specific heat polynomial coefficients

    cp_g_coeff = {[
        1.02664779928781
        -0.000177515573577911
        3.66581785159269e-07], 'kJ/(kg*K)'}; % Trace gas specific heat polynomial coefficients

    Pr_a_TLU = [
        0.720986465349271
        0.719589372441350
        ...
        0.704694042255749
        0.705614770118245]; % Dry air Prandtl number pressure vector

    Pr_w_TLU = [
        1.02327757654022
        ...
        1.01351190334830
        1.01402827396757]; % Water vapor Prandtl number pressure vector

    Pr_g_TLU = [
        0.720986465349271
        0.719589372441350
        ...
        0.704694042255749
        0.705614770118245]; % Trace gas Prandtl number pressure vector

    int_dh_T_a_TLU = {[
        0
        0.0299709934765051
        ...
        1.05826245662507
        1.07533673877425], 'kJ/(kg*K)'}; % Dry air integral of dh/T vector

    int_dh_T_w_TLU = {[
        0
        0.0551581028022933
        ...
        1.96804836665268
        2.00100413885432], 'kJ/(kg*K)'}; % Water vapor integral of dh/T vector

    int_dh_T_g_TLU = {[
        0
        0.0299709934765051
        ...
        1.05826245662507
        1.07533673877425], 'kJ/(kg*K)'}; % Trace gas 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

    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  = {1.00611201935459, 'kJ/(kg*K)'}; % Dry air specific heat at reference condition
    k_a_atm   = {25.8738283029331, 'mW/(m*K)' }; % Dry air thermal conductivity at reference condition
end

variables
    p   = {0.1, 'MPa'}; % Pressure
    T   = {300, 'K'  }; % Temperature
    x_w = 0;            % Specific humidity
    x_g = 0;            % Trace gas mass fraction
end

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

  • 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

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. 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 

See Also

Related Topics