Simcape two phase fluid custom component

I am trying to write a custom component for a non-isentropic compressor in Simscape. However, I saw a convection term that I don't understand. A snippet of the source code from the controlled_mass_flow_rate_source is shown below:

    % Specific total enthalpy for outflow
    ht_out_A == convection_A.ht_I;
    ht_out_B == convection_B.ht_I;    

    % Equate variables for internal components that calculate energy convection at ports A and B
    convection_A.mdot == mdot_A;
    convection_A.Phi  == Phi_A;
    convection_B.mdot == mdot_B;
    convection_B.Phi  == Phi_B;

    convection_A.ht_I == convection_B.ht_I;

What is the convection_A, convection_B, and the ht_I term?

Thank you!

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I will also include a snippet of my code:

% 1 is the input and 2 is the output of the block
% NI is the isentropic efficiency
% _isen indicates the case for the isentropic efficiency

% isentropic relationship
s_1 == s_2_isen;

% isentropic efficiency balance
NI*(ht_2-ht_1) == (ht_2_isen-ht_1);

% power calculation
power == mdot_A*(ht_2-ht_1);

% Specific total enthalpy for outflow
% not sure which one to use to balance the equations
(ht_2+ht_1)/2 == convection_B.ht_I;
%ht_2 == convection_B.ht_I;
%ht_1 == convection_A.ht_I;

% Equate variables for internal components that calculate energy convection at ports A and B
convection_A.mdot == mdot_A;
convection_A.Phi  == Phi_A;
convection_B.mdot == mdot_B;
convection_B.Phi  == Phi_B;

convection_A.ht_I == convection_B.ht_I;

As shown above, I am not sure what the ht_I, convection_A, and convection_B terms do.

Answer 1

[Yifeng Tang]

The convection_A & convection_B are two components that defines the behavior at the "port" or boundary of this block. If you look further down the source code, you should find something like:

% Internal components that calculate energy convection at ports A and B
components (ExternalAccess=none)
    convection_A = foundation.two_phase_fluid.port_convection(flow_area = area_A, length_scale = sqrt(4*area_A/pi));
    convection_B = foundation.two_phase_fluid.port_convection(flow_area = area_B, length_scale = sqrt(4*area_B/pi));
end

That "foundation.two_phase_fluid.port_convection" is a 2P module that defines the upwind scheme at the ports. All fluids domains have a similar component. You can select "foundation.two_phase_fluid.port_convection" and do a Ctrl+D to read its source code. The idea behind the upwind scheme maybe found on this Documentation page:

https://www.mathworks.com/help/releases/R2021a/physmod/hydro/ug/simscape-fluids-numerical-scheme.html?s_tid=doc_srchtitle

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Got it, thanks for the reply! I'll look into them.