Mass flow from the studded roller feeder
Svensson, Jan E.T.
Since 1987 the Dept. of Agricultural Engineering and the Swedish Institute of Agricultural Engineering have been working on a project aiming at increasing the precision in and the effects of fertilizer spreading. This part of the work concerns an investigation of the behaviour of granular flow from a studded roller feeder. Visual studies through a transparent housing of the studded roller feeder indicated that the granular flow could be divided into an active layer (the depth of which equals the stud height), a semi active layer (between the active layer and close to the base, flap) which is dragged along with the active layer, and a passive layer (directly against the base flap) where no continuous flow occurs (see Fig. 2.1). Figure 2.1. Active, semi active and passive layers in a studded roller feeder. Empirical flow models showed that the mean mass flow from the studded roller feeder depended on angular velocity of roller, stud height, base flap setting and median particle size. The empirical models also show that the mass flow will vary with inclination of feeder. Mechanistic flow models based on a theoretical analysis of the flow from the active and the semi active layer in the studded roller feeder showed good correlation with measured data. Analysis of the regression parameters and the residuals indicated that the models give a useful description of the flow from the feeder. The angular velocity of the roller and the stud height was found to have the biggest influence on the magnitude of the mass flow. Stud height changes both the general level of the mass flow at a given setting as well as the response of the mass flow to a change in the angular velocity of the feeder. The base flap setting was found to have a much lesser influence on the mass flow than stud height. A change in base flap setting changed the general level of the mass flow at a given setting of the feeder to a much lesser degree than a corresponding change in stud height. Furthermore, the response of the mass flow to a change in angular velocity of the feeder does not change with base flap setting. The influence of changes in particle size distribution was marginal. An explanation of this is that changes in particle size mean changes in internal friction. Since the internal friction, according to the theoretically based hypotheses, only affects the semi active layer, large changes in mass flow due to moderate changes in particle size distribution cannot be expected. The flow from the studded roller feeder will change as a function of inclination. This is a well established fact in the literature. This work show that the effects of inclination is not neglectable in a high precision spreading system where application rates are varied locally on the field. The empirical models point to a change in mass flow of ca. 0.8% per degree incline. The work also indicates that the mass flow from the feeder is dependent on the angle from the inlet into the feeder to the outlet (see chapter 1 "NOTATION" and Fig. 1.1 for definitions of angles). This angle will change as a function of inclination and as a function of base flap design (eg. base flap length). According to the mechanistic flow models, the main part of the flow stems from the active layer. Mass flow variations due to inclination affect the semi active layer. As a result of the work a new idea for feeding fertilizer with the studded roller feeder was generated. If the semi active layer could be removed, the part of the feeder which is subjected to influence of inclination and friction would probably vanish. By increasing the stud height to provide enough flow and adjusting the base flap setting to zero this idea could be evaluated. The work also identified several areas where knowledge is lacking. Examples of such areas are correlation between angle of repose and angle of internal friction, theory for granular flow and effects of confined spaces on bulk density.
granular flow; fertilizer; studded roller feeder; metering devices
Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet
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