what am i doing wrong???

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David Bento
David Bento 2022-5-23
编辑： Prathamesh 2025-7-30
I'm trying to create a simscape component in which when placing the ernergy flow it calculates the mass flow by multiplying a factor, as well as increasing the temperature of the fluid leaving the component.
component My_HeatLoad
% Mass Flow Rate Source (TL)
% This block represents an ideal mechanical energy source in a thermal
% liquid network that can maintain a constant mass flow rate regardless of
% the pressure differential. There is no flow resistance and no heat
% exchange with the environment. A positive mass flow rate causes liquid to
% flow from port A to port B.
nodes
A = foundation.thermal_liquid.thermal_liquid; % A:left
B = foundation.thermal_liquid.thermal_liquid; % B:right
end
parameters
commanded_Phi_flow = {10000, 'W'}; % Q_dot_equipment
area = {0.01, 'm^2' }; % Cross-sectional area at ports A and B
end
parameters (Access=private)
F_r = { 0.045 , 's^2/m^2' }; % Flow rate [kg/s per kW]
% ControlTemperature = {300, 'K'}; % Temperature
end
variables
T_I = {value = {298 , 'K' }, priority = priority.high}; % Temperature initial of liquid
p_I = {value = {0.101325e6, 'Pa'}, priority = priority.high} % Pressure inicial of liquid
end
% Parameter checks
equations
assert(area > 0)
end
variables (Access = protected)
% Through variables
mdot_A = {0, 'kg/s'}; % Mass flow rate into port A
mdot_B = {0, 'kg/s'}; % Mass flow rate into port B
Phi_A = {0, 'W' }; % Energy flow rate into port A
Phi_B = {0, 'W' }; % Energy flow rate into port B
end
branches
mdot_A : A.mdot -> *;
mdot_B : B.mdot -> *;
Phi_A : A.Phi -> *;
Phi_B : B.Phi -> *;
end
intermediates (Access = private, ExternalAccess = none)
% Liquid density
rho_A = convection_A.rho;
rho_B = convection_B.rho;
rho_avg = (rho_A + rho_B)/2;
% Across Variables
T_A = A.T;
T_B = B.T;
% Domain parameters
T_TLU = A.T_TLU;
p_TLU = A.p_TLU;
cp_TLU = A.cp_TLU;
% liquid properties table lookup
cp_I = tablelookup (T_TLU, p_TLU, cp_TLU, T_I, p_I, interpolation = linear, extrapolation = linear);
end
equations
let
Phi_A = commanded_Phi_flow;
in
% Commanded mass flow rate
mdot_B == F_r* Phi_A;
% Mass balance
mdot_A + mdot_B == 0;
% Energy balance
Phi_A == Phi_B;
% Temperature in B
T_B == T_A + Phi_B/(mdot_B*cp_I);
end
end
% Internal components that calculate energy convection at ports A and B
components (ExternalAccess = none)
convection_A = foundation.thermal_liquid.port_convection(flow_area = area, length_scale = sqrt(4*area/pi));
convection_B = foundation.thermal_liquid.port_convection(flow_area = area, length_scale = sqrt(4*area/pi));
end
connections
connect(A, convection_A.port)
connect(B, convection_B.port)
end
% Equate variables for internal components that calculate energy convection at ports A and B
equations
convection_A.mdot == mdot_A;
convection_A.Phi == Phi_A;
convection_B.mdot == mdot_B;
convection_B.Phi == Phi_B;
convection_B.T == T_B;
convection_A.u_I == convection_B.u_I;
end
end
what are missing?

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回答（1 个）

Prathamesh
Prathamesh 2025-7-30
编辑：Prathamesh 2025-7-30
Hi @David Bento,
I understand that the customer is trying to create a simscape component in which when placing the ernergy flow it calculates the mass flow by multiplying a factor, as well as increasing the temperature of the fluid leaving the component.
Below are required changes:
  • Change “F_r” from “s^2/m^2 (or implied kg/s per kW)” to “{0.045 / 1000, 'kg/(s*W)'}“ to correctly calculate mass flow rate in “kg/s” when multiplied by “commanded_Phi_flow” in “Watts”.
  • Modified the energy balance equation from “Phi_A == Phi_B” to “Phi_B == Phi_A + commanded_Phi_flow” to accurately model the heat (commanded_Phi_flow) being added within the component.
  • Updated the temperature calculation to “T_B == T_A + commanded_Phi_flow / (mdot_B * cp_A)“ from “Phi_B/(mdot_B*cp_I)” to use the actual added heat and the dynamic specific heat capacity “(cp_A)”, including an if condition to handle zero mass flow.
Hope this helps.

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