Biomedical Engineering Reference
In-Depth Information
Apparent density is most commonly used for design calculations because
it is the easiest to measure, and it gives the actual volume occupied by
a particle in a system. Table 3.5 gives typical apparent densities of some
woods.
Bulk Density
Bulk density is based on the overall space occupied by an amount or a group
of biomass particles:
total mass of biomass particles or stack
bulk volume occupied by biomass particles or stack
ρ bulk 5
(3.6)
Bulk volume includes interstitial volume between the particles, and
as such it depends on how the biomass is packed. For example, after
pouring the biomass particles into a vessel, if the vessel is tapped, the
volume occupied by the particles settles to a lower value. The intersti-
tial volume expressed as a function of the total packed volume is known
as bulk porosity,
A b .
To determine the biomass bulk density, we can use standards like the
American Society for Testing of Materials
(ASTM) E-873-06. This
process
involves
pouring
the
biomass
into
a
standard-size
box
(305 mm
305 mm
305 mm) from a height of 610 mm. The box is then
3
3
TABLE 3.5
Apparent Density of Some Wood Species
Shrinkage Green
to Oven-Dry
Volumetric, %
Apparent Density of
Raw Wood, kg/m 3
Type
Wood Species
Softwood
Cedar, yellow
420
6.4
Douglas fir
450
11.9
Balsam fir
340
10.7
Larch, western
550
14
Pine, ponderosa
440
10.5
Spruce, red
380
11.7
Taramack
480
11.2
Hardwood
Birch yellow
370
15.1
Maple, sugar
560
15.7
Oak, red
580
12
Source: Compiled from Mullins and McKnight (1981, p. 75.)
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