50161094 Bulk Density

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Bulk density
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Bulk density is a property of powders, granules and other "divided" solids, especially
used in reference to mineral components (soil, gravel), chemical substances,
(pharmaceutical) ingredients, foddstuff or any other masses of corpuscular or particulate
matter !t is defined as the mass of many particles of the material divided by the total
volume they occupy "he total volume includes particle volume, inter#particle void
volume and internal pore volume
$%&
'ulk density is not an intrinsic property of a material( it can change depending on how
the material is handled For e)ample, a powder poured in to a cylinder will have a
particular bulk density( if the cylinder is disturbed, the powder particles will move and
usually settle closer together, resulting in a higher bulk density For this reason, the bulk
density of powders is usually reported both as "freely settled" (or "poured" density) and
"tapped" density (where the tapped density refers to the bulk density of the powder after a
specified compaction process, usually involving vibration of the container)
Contents
$hide&
• % *oil
• + *ee also
• , -otes
• . /)ternal links
[edit] Soil
"he bulk density of soil depends greatly on the mineral make up of soil and the degree of
compaction "he density of 0uart1 is around +23g4cm5 but the bulk density of a mineral
soil is normally about half that density, between %6 and %2g4cm5 *oils high in organics
and some friable clay may have a bulk density well below %g4cm5
'ulk density of soil is usually determined on 7ore samples which are taken by driving a
metal corer into the soil at the desired depth and hori1on "he samples are then oven
dried and weighed
'ulk density 8 mass of oven dry soil4core volume
"he bulk density of soil is inversely related to the porosity of the same soil: the more pore
space in a soil the lower the value for bulk density 'ulk density of a region in the interior
of the earth is also related to the seismic velocity of waves travelling through it: for 9#
waves, this has been 0uantified with :ardner;s relation "he higher the density, the faster
the velocity
Water content
From Wikipedia, the free encyclopedia
Jump to: navigation, search
*oil composition by phase: s#soil (dry), v#void (pores filled with water or air), w#water,
a#air < is volume, = is mass
Water content or moisture content is the 0uantity of water contained in a material, such
as soil (called soil moisture), rock, ceramics, fruit, or wood Water content is used in a
wide range of scientific and technical areas, and is e)pressed as a ratio, which can range
from 6 (completely dry) to the value of the materials; porosity at saturation !t can be
given on a volumetric or mass (gravimetric) basis
Volumetric water content, >, is defined mathematically as:
where V
w
is the volume of water and V
T
8 V
s
? V
v
8 V
s
? V
w
? V
a
is the total volume
(that is soil volume ? water volume ? air space)
Gravimetric water content
$%&
is e)pressed by mass (weight) as follows:
where m
w
is the mass of water and m
b
is the bulk mass "he bulk mass is taken as the
total mass, e)cept for geotechnical and soil science applications where oven#dried soil
(m
s
, see the diagram) is conventionally used as m
b

"o convert gravimetric water content to volumetric water, multiply the gravimetric water
content by the bulk specific gravity of the material
Contents
$hide&
• % @ther definitions
o %% Aegree of saturation
o %+ -ormali1ed volumetric water content
• + =easurement
o +% Airect methods
o ++ Baboratory methods
o +, :eophysical methods
o +. *atellite remote sensing method
• , 7lassification and uses
o ,% /arth and agricultural sciences
 ,%% Cgriculture
 ,%+ :roundwater
• . *ee also
• 3 Deferences
[edit] Other definitions
[edit] Degree of saturation
!n soil mechanics and petroleum engineering, the term water saturation or degree of
saturation, S
w
is used, defined as
where E 8 V
v
4 V
T
is the porosity and V
v
is the volume of void or pore space
<alues of S
w
can range from 6 (dry) to % (saturated) !n reality, S
w
never reaches 6 or % #
these are ideali1ations for engineering use
[edit] Normalized volumetric water content
"he normalized water content, F, (also called effective saturation or S
e
) is a
dimensionless value defined by van :enuchten
$+&
as:
where > is the volumetric water content( >
r
is the residual water content, defined as the
water content for which the gradient d> 4 dh becomes 1ero( and, >
s
is the saturated water
content, which is e0uivalent to porosity, E
[edit] easurement
[edit] Direct methods
Water content can be directly measured using a known volume of the material, and a
drying oven <olumetric water content, >, is calculated
$,&
using:
where
m
wet
and m
dry
are the masses of the sample before and after drying in the oven(
G
w
is the density of water( and
V
b
is the volume of the sample before drying the sample
For materials that change in volume with water content, such as coal, the water content,
u, is e)pressed in terms of the mass of water per unit mass of the moist specimen:
However, geotechnics re0uires the moisture content to be e)pressed as a percentage of
the sample;s dry weight ie I moisture content 8 u J %66
Where
For wood, the convention is to report moisture content on oven#dry basis (ie generally
drying sample in an oven set at %63 deg 7elsius for +. hours) !n wood drying, this is an
important concept
[edit] Laboratory methods
=ain article: =oisture analysis
@ther methods that determine water content of a sample include chemical titrations (for
e)ample the Karl Fischer titration), determining mass loss on heating (perhaps in the
presence of an inert gas), or after free1e drying !n the food industry the Aean#*tark
method is also commonly used
From the Cnnual 'ook of C*"= (Cmerican *ociety for "esting and =aterials)
*tandards, the total evaporable moisture content in Cggregate (7 322) can be calculated
with the formula:
where p is the fraction of total evaporable moisture content of sample, W is the mass of
the original sample, and D is mass of dried sample
[edit] Geophysical methods
"here are several geophysical methods available that can appro)imate in situ soil water
content "hese methods include: time#domain reflectometry ("AD), neutron probe,
fre0uency domain sensor, capacitance probe, electrical resistivity tomography, ground
penetrating radar (:9D), and others that are sensitive to the physical properties of water
$.&
:eophysical sensors are often used to monitor soil moisture continuously in
agricultural and scientific applications
[edit] Satellite remote sensing method
*atellite microwave remote sensing is used to estimate soil moisture based on the large
contrast between the dielectric properties of wet and dry soil "he microwave radiation is
not sensitive to atmospheric variables, and can penetrate through clouds Clso,
microwave signal can penetrate, to a certain e)tent, the vegetation canopy and retrieve
information from ground surface $%& "he data from microwave remote sensing satellite
such as: Wind*at, C=*D#/, DCACD*C", /D*#%#+, =etop4C*7C" are used to estimate
surface soil moisture $+&
[edit] Classification and uses
=oisture may be present as adsorbed moisture at internal surfaces and as capillary
condensed water in small pores Ct low relative humidities, moisture consists mainly of
adsorbed water Ct higher relative humidities, li0uid water becomes more and more
important, depending on the pore si1e !n wood#based materials, however, almost all
water is adsorbed at humidities below LMI DH
!n biological applications there can also be a distinction between physisorbed water and
"free" water N the physisorbed water being that closely associated with and relatively
difficult to remove from a biological material "he method used to determine water
content may affect whether water present in this form is accounted for For a better
indication of "free" and "bound" water, the water activity of a material should be
considered
Water molecules may also be present in materials closely associated with individual
molecules, as "water of crystalli1ation", or as water molecules which are static
components of protein structure
[edit] Earth and agricultural sciences
!n soil science, hydrology and agricultural sciences, water content has an important role
for groundwater recharge, agriculture, and soil chemistry =any recent scientific research
efforts have aimed toward a predictive#understanding of water content over space and
time @bservations have revealed generally that spatial variance in water content tends to
increase as overall wetness increases in semiarid regions, to decrease as overall wetness
increases in humid regions, and to peak under intermediate wetness conditions in
temperature regions
$3&
"here are four standard water contents that are routinely measured and used, which are
described in the following table:
!ame !otation
Suction
"ressure
#$%kg or
k&a'
(y"ical water
content
#vol%vol'
)escri"tion
*aturated water
content
>
s
6 6+O63
Fully saturated water,
e0uivalent to effective porosity
Field capacity >
fc
P,, 6%O6,3
*oil moisture +O, days after a
rain or irrigation
9ermanent
wilting point
>
pwp
or >
wp
P%366 66%O6+3
=inimum soil moisture at
which a plant wilts
Desidual water
content
>
r
PQ 666%O6%
Demaining water at high
tension
Cnd lastly the available water content, >
a
, which is e0uivalent to:
>
a
R >
fc
P >
pwp
which can range between 6% in gravel and 6, in peat
[edit] *griculture
When a soil gets too dry, plant transpiration drops because the water is becoming
increasingly bound to the soil particles by suction 'elow the wilting point plants are no
longer able to e)tract water Ct this point they wilt and cease transpiring altogether
7onditions where soil is too dry to maintain reliable plant growth is referred to as
agricultural drought, and is a particular focus of irrigation management *uch conditions
are common in arid and semi#arid environments
*ome agriculture professionals are beginning to use environmental measurements such as
soil moisture to schedule irrigation "his method is referred to as smart irrigation or soil
cultivation
$citation needed&
[edit] Groundwater
!n saturated groundwater a0uifers, all available pore spaces are filled with water
(volumetric water content 8 porosity) Cbove a capillary fringe, pore spaces have air in
them too
=ost soils have a water content less than porosity, which is the definition of unsaturated
conditions, and they make up the subSect of vadose 1one hydrogeology "he capillary
fringe of the water table is the dividing line between saturated and unsaturated conditions
Water content in the capillary fringe decreases with increasing distance above the
phreatic surface
@ne of the main complications which arises in studying the vadose 1one, is the fact that
the unsaturated hydraulic conductivity is a function of the water content of the material
Cs a material dries out, the connected wet pathways through the media become smaller,
the hydraulic conductivity decreasing with lower water content in a very non#linear
fashion
C water retention curve is the relationship between volumetric water content and the
water potential of the porous medium !t is characteristic for different types of porous
medium Aue to hysteresis, different wetting
What is *oil =oistureT
*oil moisture is difficult to define because it means
different things in different disciplines For e)ample,
a farmer;s concept of soil moisture is different from
that of a water resource manager or a weather
forecaster :enerally, however, soil moisture is the
water that is held in the spaces between soil particles *urface soil moisture is the water
that is in the upper %6 cm of soil, whereas root 1one soil moisture is the water that is
available to plants, which is generally considered to be in the upper +66 cm of soil
Why is =easuring *oil =oisture !mportantT
7ompared to other components of the hydrologic cycle, the volume of soil moisture is
small( nonetheless, it of fundamental importance to many hydrological, biological and
biogeochemical processes *oil moisture information is valuable to a wide range of
government agencies and private companies concerned with weather and climate, runoff
potential and flood control, soil erosion and slope failure, reservoir management,
geotechnical engineering, and water 0uality *oil moisture is a key variable in controlling
the e)change of water and heat energy between the land surface and the atmosphere
through evaporation and plant transpiration Cs a result, soil moisture plays an important
role in the development of weather patterns and the production of precipitation
*imulations with numerical weather prediction models have shown that improved
characteri1ation of surface soil moisture, vegetation, and temperature can lead to
significant forecast improvements *oil moisture also strongly affects the amount of
precipitation that runs off into nearby streams and rivers Barge#scale dry or wet surface
regions have been observed to impart positive feedback on subse0uent precipitation
patterns, such as in the e)treme conditions over the central U* during the %LMM drought
and the %LL, floods *oil moisture information can be used for reservoir management,
early warning of droughts, irrigation scheduling, and crop yield forecasting
Demote *ensing of *oil =oisture
Aespite the importance of soil moisture information, widespread and4or continuous
measurement of soil moisture is all but none)istent ""he lack of a convincing approach
of global measurement of soil moisture is a serious problem" (-ational Desearch 7ouncil,
%LL+) 7learly, a need e)ists for continuous measurements of surface soil moisture with
global coverage Demote sensing of soil moisture from the vantage point of space is
advantageous because of its spatial coverage and temporal continuity, but this capability
does not yet e)ist Desearch in soil moisture remote sensing began in the mid %LV6;s
shortly after the surge in satellite development *ubse0uent research has occurred along
many diverse paths Wuantitative measurements of soil moisture in the surface layer of
soil have been most successful using passive remote sensing in the microwave region
"he potential e)ists today to retrieve soil moisture estimates from space#based
instruments at fre0uencies of about 2 :H1 (7 band) However, observations at
fre0uencies between % and , :H1 (B band) are best suited for detection of soil moisture
because energy is emitted from a deeper soil layer and less energy is absorbed or
reflected by vegetation
*oil moisture remote sensing is fraught with challenges @nly the moisture in the top few
centimeters of soil can be detected Clgorithm development is complicated by the need
for surface roughness and vegetation corrections, which are based on empirical
relationships of limited breadth /)tending ground#based techni0ues to space#based
systems re0uires innovative antenna technology !n spite of these challenges, recent
advances in aperture synthesis and thinned array technology applied at B band have
shown great promise for soil moisture mapping *cientists that the :lobal Hydrology and
7limate 7enter have been involved in e)periments to address some the challenges we
face in developing this technology

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