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The dependence of the mobility of ions in air on the relative humidity
Abstract
The relationship between relative humidity and the mobility of negative ions in air at atmospheric pressure has been examined with a view to possible applications in hygrometric measurements. The method employed was a modification of Zeleny's original method, the end of a wind channel being closed by a disc of gauze fitted with a guard ring through which a steady stream of air of definite humidity was pumped.
The motion of the negative ions due to the action of the air stream was balanced by a counter potential gradient, and the mobility was deduced from the critical potential required to produce a balance. The rate of air flow was measured by means of a Ewing ball and tube flowmeter, a hollow glass sphere being used to make it suitable for low air rates. Efforts were made to construct a direct indicating instrument by amplifying the current sufficiently to obtain deflections on a robust moving-coil indicator, but the variations in the amplification factor were found to be too serious.
... Actually, an excellent agreement between estimates and experimental results on corona current was achieved by using in (2) the values of 1.57x10 -4 m 2 /Vs and 1.62 m 2 /Vs for positive and negative ion mobility, respectively. These values are within the range of ion mobility (1.0x10 -4 ≤ μ i+ (m 2 /Vs) ≤ 2.0x10 -4 , 1.45x10 -4 ≤ μ i-(m 2 /Vs) ≤ 4.34x10 -4 ) as reported in literature [25]- [33]. Moreover, as humidity increases the ion mobility decreases [25]- [27], [29], [31]- [33]; this is more pronounced for negative ion mobility [27], [29], [33]. ...
... These values are within the range of ion mobility (1.0x10 -4 ≤ μ i+ (m 2 /Vs) ≤ 2.0x10 -4 , 1.45x10 -4 ≤ μ i-(m 2 /Vs) ≤ 4.34x10 -4 ) as reported in literature [25]- [33]. Moreover, as humidity increases the ion mobility decreases [25]- [27], [29], [31]- [33]; this is more pronounced for negative ion mobility [27], [29], [33]. Considering that the absolute humidity during the experiments varied between 18.0-22.1 gm -3 , the relatively low value of negative ion mobility of 1.62x10 -4 m 2 /Vs used in (2) could be justified. ...
Negative DC corona on conductor bundles is experimentally investigated in the coaxial configuration. The dependence of the corona characteristics, namely inception voltage and current, thus also inception field and power losses, on bundle radius and number of conductors in the bundle is assessed. The corona inception voltage of conductor bundles is highest at a bundle radius that corresponds to the minimum electric field strength at the conductor surface. The corona inception field strength of conductor bundles can be considered, with reasonable accuracy, as equal to that of the single conductor. Polarity effects on DC corona characteristics are assessed through comparisons with positive DC corona. For both polarities of applied voltage, the corona current can be accurately estimated through a modified Townsend quadratic formula using appropriate values for ion mobility.
... Usually, ion mass and mobility are used as independent parameters. Ion properties depend on the gas composition; for instance, alcohol vapor (Liu and Pui 1975) and water vapor (Griffiths and Awbery 1928;Davison and Gentry 1984;Jung and Kittelson 2005) attach to the ions, reducing their mobility and increasing their mass. It is, therefore, not surprising that there is no consensus on the values of the ion properties used in the literature. ...
Introduction Unipolar Diffusion Chargers Faraday Cage Electrometer Detection Diffusion Charging-Based Sensors Mobility Spectrometers with Electrical Detection Electrical Low Pressure Impactors List of Symbols References
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