PTV measurement of drag coefficient of fibrous particles with large aspect ratio

The aerodynamic behaviour of long aspect ratio nylon fibrous particles has been investigated experimentally while settling in air under super dilute conditions without any influence of secondary flows and at fibre Reynolds numbers of 0.5–2 based on fibre diameter. A method for laser-based measurement of the orientations and velocities of fibrous particles is also presented. The experimental apparatus employs a two-dimensional Particle Tracking Velocimetry (PTV) to calculate orientation and velocity based on the two end-points. The controlling length scale in the relationship between Reynolds number and drag coefficient was investigated and the equivalent diameter of settling fibre in air was reported. Finally the influence of volume fraction and fibre straightness were assessed.

Experimental arrangement (not to scale). The settling fibrous particles were illuminated by the laser sheet at regular intervals of time and the CCD camera used to record two images of the fibres separated by a delay of about 2.5 ms. The orientations and velocities of fibrous particles were calculated based on the two end-points.Figure optionsDownload as PowerPoint slideHighlights
► Fibre's mean settling velocity increases monotonically with volume fraction.
► Fibre's mean orientation decreases with volume fraction.
► Fibre's equivalent diameter when settling in air is investigated.
► The equations above highlights are presented.