## 1 Introduction
### Background
Successful simulation of magnetohydrodynamic (MHD) problems, in order to analyze or to design MHD systems (in the form of a channel), in the application field of electric power generation may require applying the computational fluid dynamics (CFD) method to numerically solve a set of various partial differential equations that govern the spatial distribution and the temporal variations in density, pressure, velocity vector, temperature, electric potential, and electric current density vector for the plasma gas flowing through the MHD system [20; 21; 22]. In this field of MHD and plasma gases, ordinary combustion product gases that are electrically non-conductive (not ionized) can be made electrically conductive by adding a small amount of a gas (or a compound of it) that is partly ionized at typical combustion product temperatures without other sophisticated ionization methods. This additive ionizable substance (also called the seed) can be cesium vapor, potassium vapor, or a compound containing either of them. Some of the electrons in the seed atoms are liberated under the influence of the high temperature of the carrier combustion product gases, making the gaseous mixture electrically conductive, thus making it a plasma gas [23]. Knowing the chemical composition and the electric conductivity of this plasma gas is an important step during the CFD modeling, which eventually allows for predicting the electric power output that can be extracted from the flowing plasma gas inside the MHD system, which acts as a very powerful source of electricity. Therefore, there is a relationship between CFD, MHD, combustion, and plasma simulation. In a CFD model for MHD problems, the spatial zone (the MHD channel) of high-speed (possibly supersonic speed) traveling plasma may be discretized into thousands or even millions of small finite volumes (called computational cells) or into a huge number of nodes [24; 25; 26], and the electric conductivity in each cell or node is computed as a plasma property, among other properties (such as thermal conductivity and viscosity). This is further repeated in order to advance the solution in time or to ultimately reach a steady condition, where it becomes possible to estimate how much electric power the MHD system can supply to a connected external load. It is highly advantageous that the plasma electric conductivity can be calculated by knowing only the local temperature, the local pressure (which allows knowing the number density of particles or the mass density of their species), and the local chemical composition, because these are readily obtained variables during an ongoing CFD simulation. Thus, expressing the electron-neutral collision cross sections for each involved species as a simple function of the electron temperature avoids the need for additional complex computations in case these cross sections are further modeled as depending also on electron thermal speed (speed due to temperature), which is traditionally subject to the Maxwell-Boltzmann probability distribution [27; 28]. Approximating the electron-neutral collision cross sections for a given chemical gaseous species as a function of temperature, as the only independent variable, greatly simplifies the process of computing the electric conductivity later. This simplification is common and has been adopted in different plasma studies, where a monoenergetic (electron-speed-dependent) distribution is replaced with a single constant (mean or effective) value [29; 30; 31].