PHYSICAL AND AERODYNAMIC PROPERTIES OF FLAXSEEDS FOR PROPER SEPARATION BY USING AIRSTREAM
Authors: EISSA A.H. AMER 
Published: September 2009

This study aimed to develop simple empirical equations to predict flaxseeds properties. The first part of the present study deals with the physical, aerodynamic and solid flow properties of flaxseeds which were evaluated as a function of change in moisture content from 8.60 to 23.90% dry basis (d.b.); the dimensions of the length, width and thickness varied from 4.14 to 4.32 mm, 2.03 to 2.13 mm and 0.88 to 0.93 mm, respectively. As the moisture content increased from 8.60 to 23.90% d.b., the bulk density, true density and porosity were found to decrease from 46.65 to 44.89 kg/m3, 1,244 to 1,176 kg/m3 and 46.65 to 44.89%, whereas angle of repose and terminal velocity were found to increase from 27.6 to 35.80 and 2.46 to 3.56 m/s, respectively. The static coefficient of friction on various surfaces, namely plywood, stainless steel, galvanized iron, iron and internal also increased linearly with the increase in moisture content. The results of the experimental investigation may help to optimize some engineering parameters of separation equipment.

The present work was carried out to separate flaxseed from light impurities (chaff, other debris from threshed flaxseed since the introduction of harvesting machine). It is difficult to separate seeds from straw and other foreign materials by using primary separation equipment. The difficulty comes from the narrow size and shape, angle for both of natural slope and friction between foreign materials and seeds. The second part was carried out on a series of experiments to specify the optimum conditions of separating operations which insure the highest grade of separation efficiency with minimum losses. Pneumatic separation equipment was manufactured and tested under different combinations of the following factors: airstream velocity, feed rateand sample moisture content. The performance of the equipment was evaluated by using the indices separation efficiency and percentage of seed losses.

The results of the equipment performances showed that the combinations of airstream velocity, feed rate and sample moisture content affected significantly the separation efficiency and grain losses. Airstream velocity of 2–6 m/s combined with 8.5 kg/h feed rate and 8.6% moisture content can be considered the most favorable combination values of these variables. They gave the highest grades of separation efficiency and the minimum grain losses.

PRACTICAL APPLICATIONS

There are several applications of the physical properties data. Physical attributes and aerodynamic properties are required in the design of combines as well as cleaning and grading equipment. Information about solid flow properties is needed to design handling equipment. Physical properties data are needed for the development of sensors to control machines and processes, as well as detect quality. Physical properties of crops are requisite for better design of storage and ventilation system. The physical properties that we are investigating include: (1) physical attributes such as dimensions and densities; (2) aerodynamic properties such as terminal velocity and drag coefficient; and (3) solid flow properties like angles of repose and internal friction.