New Particle Surface Area

Ideally, size reduction energy could be based on particle sizes to provide comparative measures when different particle size spectra were encountered. One approach is to use “new particle surface area” as the basis.

An approach to calculate surface area was examined. Oak wood chips samples before and after grinding (hammer mill) were sieved with 2-mm and 1-mm sieves. Three sub-samples were obtained: > 2mm(sieve), 1-2 mm (sieve), < 1mm (sieve). These sub samples were individually analyzed, and data were pooled based on mass fractions to calculate representative particle sizes for samples before and after grinding.

For the second method the effect of particle shape and size was examined in determining particle surface area:

For particle assumption 1, the > 2mm subsample particles were assumed flat rectangle with assumed major dimensions of the square root of upper sieve size times lower sieve opening width, with upper sieve assumed as 3 mm. Particle thickness was measured as 0.289 mm for > 2mm particles. 1-2mm and <1mm subsamples were assumed as spherical of diamater size determined as the square root of upper sieve size times lower sieve opening width. 

For particle assumption 2, subsample > 2mm particles were assumed flat rectangle with assumed major dimensions of the square root of upper sieve size times lower sieve opening width, with upper sieve assumed as 3 mm. Particle thickness was measured as 0.289 mm for > 2mm particles. Subsample 1-2 mm were assumed as flat rectangle of measured particle thickness, length and width of assumed sieve representative size which equals to the square root of product of upper and low seive sizes, Particle on seive  < 1mm were assumed as flat rectangle of measured particle thickness, length and width of assumed sieve representative size which equals to the square root  of product of upper and low seive sizes.

For particle assumption 3, subsample > 2mm particles were assumed flat rectangle with assumed major dimensions of the square root of upper sieve size times lower sieve opening width, with upper sieve assumed as 3 mm. Particle thickness was measured as 0.289 mm for > 2mm particles. Subsample 1-2 mm were assumed as flat rectangle of one-half (1/2) measured particle thickness, length and width of assumed sieve representative size which equals to the square root of product of upper and low seive sizes, Particle on seive  < 1mm were assumed as flat rectangle of one-half (1/2) measured particle thickness, length and width of assumed sieve representative size which equals to the square root  of product of upper and low seive sizes.

Using the ASAE standard method to calculate the new generated area, the area is 10.87 (m2/kg) of before grinding and 11.93 (m2/kg) of after grinding, the new generated surface area per weight increases 9.8%.

Particle assumptions for input and output are shown in Tables 1 and 2 for the second area calculation method based on particle shapes.