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Calculation of Transport Properties of Dense Fluids Using Modified Enskog Theory (MET) and Appropriate Equation of State (EoS)

Ansari, Parisa | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44040 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Parsafar, Gholam Abbas
  7. Abstract:
  8. In this research, a method based on the modified Enskog theory (MET) and some equations of state has been used to calculate the transport properties of some dense fluids. The main limitation to using the MET is the lack of experimental data for the co-volume, b0, that are substituted from the hard sphere (HS) theory, and the zero density transport properties that are substituted from the kinetic theory of gases for the HS in the MET expression, because of the fact that dense fluids behave more and less like a HS fluid. So a quadratic expression for both ηY/(√T ρ) and λY/(ρ√T) (C_(V,m)+ (9/4)R) in terms of Y at high densities (ρ > ρc) for each isotherm is expected, where Y = (T (∂p/∂T))/ρRT – 1. In order to evaluate the quadratic expressions mentioned above for the viscosity and thermal conductivity, we have used experimental values for densities and the transport properties to calculate Y from the differentiation of pressure given by the empirical equation of state, equation III, LIR , LIR(2) and LIR(3) . We have applied these EoSs to calculate the transport properties by plotting the deviation curves for thermal pressure, viscosity and thermal conductivity. Since both ηY/(√T ρ) and λY/(ρ√T) (C_(V,m)+ (9/4)R) in terms of the calculated Y from the empirical EoS and EoS III fall onto a common curve for different isotherms and the minimum relative errors are obtained for EoS III in the deviation curves. EoS III which predicts many properties of the dense systems that no deviation is observed for and doesn’t have any limitation for temperature and density expect near the critical point, can be an appropriate EoS to predict the transport properties. In the next section, we have found that a, b, c, i, j, and k- coefficients of the quadratic equations- may be temperature dependent for real fluids. As a result the dependency of the obtained coefficients from the empirical EoSs to temperature for spherical molecules like methane and argon can be introduced by the third-order polynomial equations; however for non-spherical molecules like water the third-order equations can’t be used. The dependency of the coefficients to temperature decreases by increasing the temperature. Owing to the fact that spherical real fluids behave like the HS fluids at very high temperatures, such observations are expected; Because the coefficients are related to the HS diameter and are independent of temperature for an HS fluid. We have used this approach to predict the coefficients of the quadratic equations for methane, argon, oxygen, nitrogen and water at different densities (ρ > ρ_c) and temperatures (T > T_c ), using appropriate EoSs. So by using the experimental data obtained for the transport properties for one fluid and the equation III used to calculate Y for a spherical dense fluid, we may be able to calculate the transport properties of that fluid
  9. Keywords:
  10. Transport Properties ; Linear Isotherm Regularity ; Cubic State Equations ; Modified Enskog Theory (MET)

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