SIZE AND SHAPE RELATED CHARACTERISTICS OF ALFALFA GRIND

Particle size distribution of a commercial alfalfa grind was determine d by sieving test. Shape characteristics of alfalfa grind were examine d using scanning electron microscope and image processing technique. T he particle size was best described by the log-normal distribution bas ed on the curve fitting results of various distribution functions. The median size (geometric mean diameter) of alfalfa grind was 238 mu m w ith a standard deviation of 166 mu m. Particle density measured by air comparison pycnometer ranged from 1390 to 1599 kg/m(3) (average 1453 +/- 62 kg/m(3)). Surface area of the alfalfa grind measured using the BET method with nitrogen sorption and calculated following the ASAE S3 19.2 was 0.750 +/- 0.259 m(2)/g and 0.0215 m(2)/g, respectively. Scann ing electron micros copy (SEM) and computer-aided image analysis were used to characterize the particles retained on individual test sieves of nominal apertures from 20 to 850 mu m. It was found that the mean p article projection length ranged from 0.242 to 0.979 mm, width from 0. 034 to 0.425 mm, area from 0.002 to 0.295 mm(2), perimeter from 0.188 to 2.421 mm, and sphericity (roundness) from 0.54 to 0.64. A statistic al regression analysis showed that these parameters were linear with s ieve openings.