Error: No. of variables exceed no. of equations (how to count variables)

Here is my code for a counterflow water/water heat exchanger based on LMTD method.

The error which I am receiving is that no. of variables are exceeding the no. of equations. But I can't think of any equation which I missed as it is a very simple model. Can someone take a look at it and suggest any equation which I have missed.

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component counterflow_HX

% Heat Exchanger

% Ideal Counter flow heat exchanger based on LMTD method

nodes

A1 = foundation.thermal_liquid.thermal_liquid; % A1:left

B1 = foundation.thermal_liquid.thermal_liquid; % B1:left

B2 = foundation.thermal_liquid.thermal_liquid; % B2:right

A2 = foundation.thermal_liquid.thermal_liquid; % A2:right

end

parameters

Cp = { 4.2, 'J/g/K'}; % Specific heat

UA = { 0.34, 'J/s/K'}; % Product of heat transfer coefficient & area

end

variables

M1 = { 0.09, 'kg/s' }; % hot side mass flow

M2 = { 0.275, 'kg/s' }; % cold side mass flow

Phi1 = { 0, 'J/s' }; % hot side duty

Phi2 = { 0, 'J/s' }; % cold side duty

end

branches

M1 : A1.mdot -> B1.mdot;

M2 : A2.mdot -> B2.mdot;

Phi1: A1.Phi -> B1.Phi;

Phi2: A2.Phi -> B2.Phi;

end

    equations

    let

    p_A1 = A1.p;

    T_A1 = A1.T;

    p_A2 = A2.p;

    T_A2 = A2.T;

    p_B1 = B1.p;

    T_B1 = B1.T;

    p_B2 = B2.p;

    T_B2 = B2.T;

    LMTD = ((T_A1 - T_B2) - (T_A2 - T_B1))/ (log ((T_A1 - T_B2) / (T_A2 - T_B1)));

    in

      Phi1 == M1 * Cp * (T_A1 - T_B1)
      Phi2 == M2 * Cp * (T_A2 - T_B2)
      Phi1 == Phi2
      p_A1 == p_B1
      p_A2 == p_B2
      Phi1 == UA * LMTD

    end

end
end

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[Abhiram Bhanuprakash]

Hi Muhammad Zain,

The code which you have posted does not look like MATLAB code. Can you tell which language it is, and what is the relation between this and MathWorks products?

Abhiram

[Muhammad Zain Haider Ali]

Abhiram, This is the SIMSCAPE language, which used to model physical systems.

[Andreas]

Could you share the working code?

Answer 1

[Drew Davis]

It appears you are missing equations for the "M1" and "M2" variables. See this example.