Marzouk Osama A
College of Engineering, University of Buraimi, Al Buraimi, Sultanate of Oman.
Heliyon. 2024 May 22;10(11):e31697. doi: 10.1016/j.heliyon.2024.e31697. eCollection 2024 Jun 15.
A complete model for estimating the electric conductivity of combustion product gases, with added cesium (Cs) or potassium (K) vapor for ionization, is presented. Neutral carrier gases serve as the bulk fluid that carries the seed material, as well as the electrons generated by the partial thermal (equilibrium) ionization of the seed alkali metal. The model accounts for electron-neutral scattering, as well as electron-ion and electron-electron scattering. The model is tested through comparison with published data. The model is aimed at being utilized for the plasma within magnetohydrodynamic (MHD) channels, where direct power extraction from passing electrically conducting plasma gas enables electric power generation. The thermal ionization model is then used to estimate the electric conductivity of seeded combustion gases under complete combustion of three selected fuels, namely: hydrogen (H), methane (CH), and carbon (C). For each of these three fuels, two options for the oxidizer were applied, namely: air (21 % molecular oxygen, 79 % molecular nitrogen by mole), and pure oxygen (oxy-combustion). Two types of seeds (with 1 % mole fraction, based on the composition before ionization) were also applied for each of the six combinations of (fuel-oxidizer), leading to a total of 12 different MHD plasma cases. For each of these cases, the electric conductivity was computed for a range of temperatures from 2000 K to 3000 K. The smallest estimated electric conductivity was 0.35 S/m for oxy-hydrogen combustion at 2000 K, with potassium seeding. The largest estimated electric conductivity was 180.30 S/m for oxy-carbon combustion at 3000 K, with cesium seeding. At 2000 K, replacing potassium with cesium causes a gain in the electric conductivity by a multiplicative gain factor of about 3.6 regardless of the fuel and oxidizer. This gain factor declines to between 1.77 and 2.07 at 3000 K. Based on the findings of this research study, the four analyzed factors to increase the electric conductivity of MHD plasma can be listed by their significance (descending order) as (1) type of additive seed type (cesium is better than potassium), (2) temperature (the higher the better), (3) carbon-to-hydrogen ratio of the fuel (the higher the better), and finally (4) the oxidizer type (air is generally better than pure oxygen). The relative size of the two electric conductivity components (due to neutrals scattering and Coulomb scattering) at various plasma conditions are discussed, and a threshold of 10 (0.001 %) electrons mole fraction is suggested to safely neglect Coulomb scattering.
本文提出了一个完整的模型，用于估算燃烧产物气体的电导率，该气体添加了铯（Cs）或钾（K）蒸汽用于电离。中性载气作为携带种子材料以及由种子碱金属的部分热（平衡）电离产生的电子的主体流体。该模型考虑了电子 - 中性散射以及电子 - 离子和电子 - 电子散射。通过与已发表的数据进行比较对该模型进行了测试。该模型旨在用于磁流体动力学（MHD）通道内的等离子体，在该通道中，从通过的导电等离子体气体中直接提取电能可实现发电。然后使用热电离模型来估算三种选定燃料（即氢气（H）、甲烷（CH）和碳（C））完全燃烧情况下种子燃烧气体的电导率。对于这三种燃料中的每一种，应用了两种氧化剂选项，即空气（按摩尔计含21%分子氧、79%分子氮）和纯氧（富氧燃烧）。对于（燃料 - 氧化剂）的六种组合中的每一种，还应用了两种类型的种子（基于电离前的组成，摩尔分数为1%），从而产生总共12种不同的MHD等离子体情况。对于这些情况中的每一种，在2000K至3000K的温度范围内计算电导率。估计的最小电导率是在2000K时钾种子化的氢氧燃烧情况下的0.35S/m。估计的最大电导率是在3000K时铯种子化的氧碳燃烧情况下的180.30S/m。在2000K时，无论燃料和氧化剂如何，用铯代替钾会使电导率增加约3.6的倍增增益因子。该增益因子在3000K时降至1.77至2.07之间。基于本研究的结果，按重要性（降序）列出的用于提高MHD等离子体电导率的四个分析因素为：（1）添加剂种子类型（铯比钾好），（2）温度（越高越好），（3）燃料的碳氢比（越高越好），最后是（4）氧化剂类型（空气通常比纯氧好）。讨论了在各种等离子体条件下两个电导率分量（由于中性散射和库仑散射）的相对大小，并建议10（0.001%）电子摩尔分数的阈值以安全地忽略库仑散射。
