Error calculating specific heat and constant pressure

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I get an error when compiling my Simscape model using a real gas specification.
Elements of Specific heat at constant pressure table must be greater than (Temperature) * (Specific volume) * (Isothermal bulk modulus) * (Isobaric thermal expansion coefficient)^2.
I verified my real gas data using the expression:
cv_TLU2 = cp_TLU2 - repmat(T_TLU2(:), 1, n) .* alpha_TLU2.^2 .* beta_TLU2 ./ rho_TLU2;
In all cases the value that I get from this is positive and also in all cases Cp is greater than the product "(Temperature) * (Specific volume) * (Isothermal bulk modulus) * (Isobaric thermal expansion coefficient)^2".
In fact I checked the output of that expression against known Cv data for this gas and it it matches exactly so I can't understand how Simscape finds an error with this.

Risposta accettata

TiffyEng
TiffyEng il 1 Feb 2021
This has been resolved. The wrong units were used to generate the Isobaric Thermal Expansion array.
  1 Commento
wwmathchat
wwmathchat il 6 Lug 2021
I'm having the same problem. Could you clarify whether you fixed the problem by changing your inputs or the gas_properties.ssc file?
I'm using MPa for the Isothermal bulk modulus (beta_TLU2). From what I can tell, the units of this equation are not consistent, unless Isothermal bulk modulus is in kPA. Is this correct?
cv_TLU2 = cp_TLU2 - repmat(T_TLU2(:), 1, n) .* alpha_TLU2.^2 .* beta_TLU2 ./ rho_TLU2;

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