What is porosity (percentage of void) of powder bed? 

-There are spaces among particles in powder bed, as a result the space 1cm 3 of true density particles actually occupies is more than 1cm 3 . If it is 1.25cm 3 , then the filling degree is 1/1.25=0.8 and therefore the powder bed porosity is 1-0.80=0.20. 



HMK-22 Fisher Sub-Sieve Sizer
http://www.aimsizer.com/particle_size_analyzer_fisher_sub_sieve_sizer_0.2um_50um.html