Flowability testing for aerial lime

Abstract

The Civil Aviation Authority (CAA) requires that topdressing aircraft are capable of jettisoning 80% of the aeroplane’s maximum hopper load within five seconds of the pilot initiating the jettison action. For granulated materials that are nearly uniform in size and of spherical shape, this requirement is not a problem, as such materials have good flowability. Agricultural lime however, is typically a fine powder which can have poor flowability, particularly when wet. Two different devices were tested for their ability to assess lime flowability. Lime from six different sources was evaluated. The lime was dried in an oven, and then water added in discrete amounts, so that the flowability of the lime samples could be assessed at moisture levels from 0 to 5% by mass. Tapping and compressing the lime before testing was used to simulate conditions at the bottom of an aircraft hopper. The dried lime samples were also used for measuring the particle size distribution using an Endecotts sieve shaker. From the sieving data, the only particle size distribution parameter that correlated strongly with flowability test results was the Uniformity Index, a measure of the standard deviation of the size distribution.