Terminal Velocity of Corn Stover Stem Fractions

Abstract

Highlights Terminal velocity was measured for small, standardized sizes of corn stover stem fractions with a vertical wind tunnel built to aerodynamically suspend particles. Mean terminal velocity ranged from 2.84 m s-1 to 7.74 m s-1 for dry pith-internode and wet rind-node fractions, respectively. Anticipated separation of corn stover stem particles using terminal velocity differences was viable for dry (11% w.b.) particles of pith, rind, node, and internode. But, many wet (43% w.b.) fractions had similar terminal velocities, thereby reducing separation propensity. Abstract. Terminal velocity of corn stover stem fractions was determined for particles standardized to match particle sizes (1.3 cm long x 0.31 cm diameter) of switchgrass nodes and internodes. The practical application was to measure the potential aerodynamic conditions for sorting and separating size-reduced anatomical components of pith versus rind, node versus internode, and at two moisture contents (11% and 43%, wet basis). Terminal velocities grouped by dry pith, wet pith, dry rind, and wet rind resulted in a trend of increased mean terminal velocities of 3.28, 5.31, 6.38, and 7.68 m s-1, respectively, when averaged across node and internode. The increased moisture and the selection of the rind component had increased terminal velocity that was attributed to increased particle density. Terminal velocity for a node was generally statistically greater than that of an internode for a given condition, except for the statistically-equal terminal velocities for node and internode of wet rind. Also, terminal velocity for internode of dry pith and of wet pith were statistically equal. Thus, exceptions to the general trends were discovered. Mean terminal velocity ranged from 2.84 m s-1 to 7.74 m s-1 for dry pith-internode and wet rind—node particles, respectively. Practical separation of corn stover stem particles using terminal velocity differences was viable for dry (11% w.b.) particles of pith, rind, node, and internode. Many terminal velocities of wet (43% w.b.) fractions were statistically equal leaving only wet pith-internode available at this moisture for aerodynamic separation. Particle density varied almost 10-fold for the experiment, and this was attributed to the various anatomical component and range of moisture content. Highly significant correlations of particle density with terminal velocity may have represented a cause-and-effect factor. Keywords: Anatomical component, Biomass property, Corn Stover, Physical experiment, Separation, Sorting, Vertical wind tunnel.