How to estimate the transport properties: dynamic viscosity, thermal conductivity and diffusivity of a gas, if measurements are not available?
Tagged: 16, cfx, fluiddynamics, General, General  CFX, materialproperties


January 25, 2023 at 7:16 amFAQParticipant
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, p2223, for spherical nonpolar molecules, we can estimate the LennardJones 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 B2, 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 tworange NASA polynomials (S. Gordon and B.J. McBride, “Computer Program for Calculation of Complex Chemical Equilibrium Composition, Rocket Performance, Incident and Reflected Shocks and ChapmanJouguet Detonations”, NASA SP273 (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 7.12118611E042.70003073E07 4.14986299E112.31188294E15 2 1.28568767E+04 9.07351144E+00 2.48571711E+00 1.50647525E045.37267333E07 3 7.20921065E102.50205558E13 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 = 1.50647525E04 a3 = 5.37267333E07 a4 = 7.20921065E10 a5 = 2.50205558E13 and the upper for 1000K < T < 6000K a1 = 2.08851053E+00 a2 = 7.12118611E04 a3 = 2.70003073E07 a4 = 4.14986299E11 a5 = 2.31188294E15 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.

Introducing Ansys Electronics Desktop on Ansys Cloud
The Watch & Learn video article provides an overview of cloud computing from Electronics Desktop and details the product licenses and subscriptions to ANSYS Cloud Service that are...
How to Create a Reflector for a Center HighMounted Stop Lamp (CHMSL)
This video article demonstrates how to create a reflector for a center highmounted stop lamp. Optical Part design in Ansys SPEOS enables the design and validation of multiple...
Introducing the GEKO Turbulence Model in Ansys Fluent
The GEKO (GEneralized KOmega) turbulence model offers a flexible, robust, generalpurpose approach to RANS turbulence modeling. Introducing 2 videos: Part 1 provides background information on the model and a...
Postprocessing on Ansys EnSight
This video demonstrates exporting data from Fluent in EnSight Case Gold format, and it reviews the basic postprocessing capabilities of EnSight.
 How to overcome the model information incompatible with incoming mesh error?
 How to create and execute a FLUENT journal file?
 What are the requirements for an axisymmetric analysis?
 How can I Export and import boxes / Systems from one Workbench Project to another?
 How can I select interior faces and other entities that are inside the model?
 Lefthanded faces troubleshooting
 What is a .wbpz file and how can I use it?
 Skewness in ANSYS Meshing
 Error: Update failed for the Mesh component in Fluid Flow (Fluent). Error updating cell Mesh in system Fluid Flow (Fluent). View the messages in the Meshing editor for more details.
 Running Python Script from Workbench
© 2024 Copyright ANSYS, Inc. All rights reserved.