Fundamentals of particle charging by free electrons in electrical coronas

气溶胶的带电在许多技术应用和气溶胶测量中是一个重要的过程。基于扩散带电和场带电的气溶胶正负离子带电动力学是众所周知的。但在某些情况下，气雾剂的充电速度要比预期快得多，水平也比预期高得多。一般来说，这种效应可以归因于自由电子对气溶胶的充电。这种所谓的气溶胶“电子充电”现象，特别是在电负性气体浓度较低或温度较高的情况下会出现。在这些情况下，负气体离子的形成被推迟或不发生。因此，电晕放电中的电流输运将部分或几乎完全由自由电子发生。在静电场中，自由电子将达到很高的(非平衡)电子温度，气溶胶粒子通过电子扩散充电可以达到很高的带电水平。到目前为止，还缺乏对气溶胶带电的系统研究。此外，缺乏对技术上相关的混合气体中的电子充电进行理论预测所需的基本数据。在该项目内，应提供和验证用于对电晕放电中气溶胶的电子充电进行定量建模的基本原理。这将首先使用作为技术上相关的混合气体模型的系统N_2-O_2-H_2O和亚微米气溶胶来完成。对于电荷载流子动力学的测量，经典的漂移管实验将适应这种条件。同时，气溶胶充电动力学的测量将首先在均匀静电场中的漂移管中进行。进一步的验证将在线管几何形状的电晕放电中进行。

The electrical charging of aerosols is an important process in many technical applications and in aerosol measurements. The kinetics of aerosol charging by positive and negative gas ions based on the mechanisms of diffusion charging and field charging is well known. But in some situations aerosols are being charged much faster and to a much higher level than expected. As a rule, this effect can be attributed to aerosol charging by free electrons. This so called “Electronic Charging” of aerosols is to be found especially with low concentrations of electronegative gases or with elevated temperatures. In these cases the formation of negative gas ions is delayed or does not take place. Hence, the current transport in a corona discharge will occur in part or almost completely by free electrons. In electrostatic fields, the free electrons will reach very high (non-equilibrium) electron temperatures, and aerosol particles can reach very high charging levels by electronic diffusion charging. So far, there is a lack of systematic investigations on electronic charging of aerosols. In addition, there is a lack of basic data which would be needed for a theoretical prediction of electronic charging in technically relevant gas mixtures. Within the project, the fundamentals for modelling quantitatively the electronic charging of aerosols in corona discharges shall be provided and validated. This will be done first with the system N2-O2-H2O as a technically relevant gas mixture model and with submicron aerosols. For measurements of the charge carrier kinetics, classical drift tube experiments will be adapted to the conditions. As well, measurements of aerosol charging kinetics will be done first in a drift tube within a homogeneous electrostatic field. Further validations will be done with corona discharges in a wire-tube-geometry.