Parameters of air flow over the upper sieve in the cleaning chamber

摘要

The value and direction of the resultant vector of the airflow coming out of the upper sieve, depending on changes in the gap between the blinds in purification of the combine harvester, is assessed. The volume and direction of the resultant vector of the airflow, as well as its components were evaluated in the study. Dynamic pressure was measured over a sieve with Pitot tubes in 6 points along the length, in each section at a distance of 50 mm from the blinds mounting axes. During the purification with a serial sieve by S_(VT) = 7...13 mm speed is almost constant, but when Sw >13 mm, it intensively reduces from 4 to 2.50 m/s. This mentioned pattern of speed changes of serial sieves affects undoubtedly negatively on the separation of grain. In fact, by increasing of the supply of straw heap, S￥r gap between the louvers is increased to reduce static resistance of network. However the increase of S_(VT) reduces the air flow speed and its loosening impact on heap. Thus, one reason for intensive grain losses increase in empty glume by higher feed rates of heap of straw is a decrease in the function v (Sw). Under the influence of the vertical component of velocity and vibrations of sieves the heap layer comes into a quasi-fluid state and the factional force between particles decreases. It facilitates the passage of grains through the layer. During the tests in purification units of harvesters measurements of air flow velocity over the sieves were made.