Free Courses Fluids Structures 3D Design Electronics Materials Photonics Student Teams STEM Python Missions Optical Installation Indo Kursus My Courses

[FAQ]

Some gases are rare or have low vapour pressure and so measurements of transport properties may not be available from the literature. Dynamic Viscosity ============== Transport properties can still be estimated based on the kinetic theory of gases. For example, Poling. Prausnitz and O’Connell, “The Properties of Gases and Liquids” lists critical constants for many substances. Then from Bird, Stewart and Lightfoot, “Transport Phenomena”, Wiley NY 1960, p22-23, for spherical non-polar molecules, we can estimate the Lennard-Jones parameters: epsilon/k = 0.77*Tc where the critical temperature, Tc is in K, the characteristic diameter, sigma in Angstroms, = 0.841*Vc^(1/3) with the critical volume, Vc in cm3/mol (or sigma = 2.44(Tc/pc)^(1/3) with the critical pressure, pc, in atm). The dynamic viscosity for a gas at low density is then given by: Mu = 2.6693×10^-6*(MT)^(1/2)/sigma^2*Omega in kg/m/s, where M is the molecular weight in kg/kmol and Omega can be found as a function of epsilon /k in Table B-2, p746. Specific Heat Capacity ================= The specific heat at constant pressure, Cp, is usually easily found in the literature, for example, Alexander Burcat and Branko Ruscic, Ideal Gas Thermochemical Database with updates from Active Thermochemical Tables in ftp://ftp.technion.ac.il/pub/supported/aetdd/thermodynamics mirrored at http://garfield.chem.elte.hu/Burcat/burcat.html has NASA polynomials for many materials in the form of two-range NASA polynomials (S. Gordon and B.J. McBride, “Computer Program for Calculation of Complex Chemical Equilibrium Composition, Rocket Performance, Incident and Reflected Shocks and Chapman-Jouguet Detonations”, NASA SP-273 (1971)),. So for example, THERMO 200.0 1000.0 6000.0 Br J6/82BR 1 0 0 0G 200.000 6000.000 1 2.08851053E+00 7.12118611E-04-2.70003073E-07 4.14986299E-11-2.31188294E-15 2 1.28568767E+04 9.07351144E+00 2.48571711E+00 1.50647525E-04-5.37267333E-07 3 7.20921065E-10-2.50205558E-13 1.27092168E+04 6.86030804E+00 1.34535890E+04 4 END The lower polynomial is valid for 200K < T < 1000K: Cp = R/M*(a1+a2*T+a3*T^2+a4*T^3+a5*T^4), where a1 = 2.48571711E+00 a2 = 1.50647525E-04 a3 = -5.37267333E-07 a4 = 7.20921065E-10 a5 = -2.50205558E-13 and the upper for 1000K < T < 6000K a1 = 2.08851053E+00 a2 = 7.12118611E-04 a3 = -2.70003073E-07 a4 = 4.14986299E-11 a5 = -2.31188294E-15 and R is the universal gas constant (8314.41 J/kmol/K) and M is the molecular weight. Thermal Conductivity ================ You can estimate k from Bird, Stewart and Lightfoot, p257. the Eucken formula gives k = (Cp + 5/4*R/M)*Mu, which for monotonic gases can be simplified to k = 15/4*(R/M)*Mu.