I have read many research paper analyzing the entropy generation due to heat-mass transfer. In their study they have considered liquid (water, EG, Casson fluid and etc.) as the working fluid. They have use the term gas constant/universal gas constant in entropy term. However, the article entitled " The thermodynamic design of heat and mass transfer processes and devices" discusses the entropy generation by considering gas flow and, hence used the term gas constant/universal gas constant. Is it justified to use the gas constant for liquid flow? Please let me know.
Thank you Ms. Kritika.
Can you suggest some literature that explains the use of a gas constant in the entropy generation using liquid flow?
It is an interesting question that you ask from the standpoint of computational physics. Another equivalent interpretation of the gas constant R is taken from regular thermodynamics. R is the difference between the constant pressure and volume specific heats, i.e., R = Cp - Cv. This form for an equation of state lends itself readily to gases which are very compressible. In a rough approximation, liquids are incompressible. This is really not true because under extreme enough conditions, almost anything is compressible. Still, the perfect gas form,
PV = Rho RT is not suitable for liquids because another assumption for the equation of state is that it ignores intermolecular forces. With the high mean free path distances common to gases (in most cases), this approximation is valid, but for liquids it is not. At high gas pressures/densities, it also fails. The functioning of the equation can be improved by introducing the notion of a covolume, an additional term that provides a sense of intermolecular force. This is manifested in the so-called Virial equation of state, i.e., PV = kbT + , where indicates an average and constitutes the covolume term. Here, the Boltzmann Constant kb acts in lieu of R, but a similar form containing R can be derived. One can work out a connection to entropy via the thermodynamics for the Virial equation of state. You can see the notion of a covolume appear in the Peng-Robinson EOS mentioned by Kritika Singh Somvanshi. I do not know if this will be helpful to you, but it's a great topic for discussion. The reference I use is: Computer Simulation of Liquids, 2nd Edition, Allen, M.P. and Tildesley, D.J., Oxford University Press, 2017. Best wishes.
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