Abstract
The physical characteristics of particles (seeds and fertilisers) can strongly influence their movements both in seeding and spreading machines and in the air. It is therefore essential to study these particles when constructing such machines. In this respect the size, shape, coefficient of friction and aerodynamic resistance of particles are of great importance.Due to their irregular shape, determining the size of particles is a troublesome process. A precise description of particles has to include several sizes and can be obtained from their screen size. Many physical properties of particles are relevant during movement in the air, but the aerodynamic resistance coefficient is the most important (Hofstee et al., 1990). Two types of wheat and four types of fertiliser particles were investigated (supported by the National Scientific Foundation OTKA, T-026482). An elutriator was designed and constructed (Csizmazia et al., 2000), in which an airflow is supplied by a centrifugal fan. Air velocity was measured with a thermal sensor. Particle sizes, mass and terminal air velocity were measured. The influence of the aerodynamic resistance coefficient on the particles’ motion is also discussed.
Highlights
There have been experiments in the Department of Agricultural Engineering of the Centre of Agricultural Sciences, Faculty of Agronomy of Debrecen University for years to determine the physical characteristics of fertilisers, seed-corns and materials used in agriculture and the even and accurate application of seed-corns and fertilisers
The critical air velocity of the grains was measured and the seeds were divided into 7-17 groups, according to their critical air velocity
The aerodynamic resistance coefficient k, and the terminal velocity plotted against ma values were calculated
Summary
We tried to identify the factors influencing the movement of grains in the air. Thousand seed weight and grain sizes differed significantly among the groups, formed on the basis of critical air velocity. − The thousand seed weight, generally used in practice, is an average figure representing grains with significantly different masses. − For the various wheat types, we measured different thousand seed weights for the same critical air velocity. − For the various wheat types, we measured different grain sizes for the same critical air velocity. − We can conclude that the grain’s movement in the air is influenced by others factors than thousand seed weight and grain size. The particle sizes and mass, terminal air velocity was measured. The aerodynamic resistance coefficient k, and the terminal velocity plotted against ma values were calculated
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