Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Water Content shopping experience:
1. Compare - without doubt the biggest advantage that the Water Content offers shoppers today is the ability to compare thousands of Water Content at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Water Content? Wrong! If the Water Content is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Water Content then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Water Content? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Water Content and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Water Content wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Water Content then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Water Content site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Water Content, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Water Content, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
Water content or
moisture content is the quantity of
water contained in a material, such as soil (called
soil moisture), Rock (geology),
ceramics, or wood on a volumetric or gravimetric basis. The property is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials'
porosity at saturation.
Volumetric water content, θ, is defined mathematically as:
\theta = \frac{V_w}{V_b}
where V_w is the volume of water and V_b (or V_s for soil) is the bulk material volume. Water content may also be based on its mass or weight, thus the
gravimetric water content is defined as:
u = \frac{m_w}{m_b}
where m_w is the mass of water and m_b (or m_s for soil) is the bulk material mass.
To convert gravimetric water content to volumetric water, multiply the gravimetric water content by the bulk density of the material.
Measurement
Direct methods
Volumetric water content can be directly measured using a known volume of the material, and a drying oven. Volumetric water content, θ, is calculated using:
\theta = \frac{m_{wet}-m_{dry-->{\rho_w \cdot V_b}
where
m_{wet} and m_{dry} are the
masses of the sample before and after drying in the oven;
\rho_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
wood, the water content,
u, is expressed in terms of the mass of water per unit mass of the moist specimen:
u = \frac{m_{wet} - m_{dry-->{m_{wet-->
Laboratory methods
Other methods that determine water content of a sample include chemical titrations (for example the
Karl Fischer titration), determining mass loss on heating (perhaps in the presence of an inert gas), or after freeze drying. In the food industry the
Dean-Stark apparatus is also commonly used.
From the Annual Book of ASTM (American Society for Testing and Materials) Standards, the total evaporable moisture content in Aggregate (C 566) can be calculated with the formula:
p = 100(W-D)/D
where:
p = total evaporable moisture content of sample, percent,W = mass of original sample, g, andD = mass of dried sample, g.
Geophysical methods
There are several Geophysics methods available that can approximate
in situ soil water content. These methods include: time-domain reflectometry (TDR),
neutron probe, frequency domain sensor,
capacitance probe, electrical resistivity tomography, and others that are sensitive to the Water (molecule). Geophysical sensors are often used to monitor soil moisture continuously in agricultural and scientific applications.
Satellite Remote Sensing Method
Satellite microwave remote sensing is used to estimate soil moisture based on the large contrast between the dielectric properties of wet and dry soil. The data from microwave remote sensing satellite such as: WindSat, AMSR-E, RADARSAT, ERS-1-2 are used to estimate surface soil moisture .
Classification and uses
Moisture may be present as adsorbed moisture at internal surfaces and as capillary condensed water in small pores. At low relative humidities, moisture consists mainly of adsorbed water. At higher relative humidities, liquid water becomes more and more important, depending on the pore size. In wood-based materials, however, almost all water is adsorbed at humidities below 98% RH.
In biological applications there can also be a distinction between physisorbed water and free water — the physisorbed water being that closely associated with and relatively difficult to remove from a biological material. The method used to determine water content may affect whether water present in this form is accounted for.
Water molecules may also be present in materials closely associated with individual molecules, as "water of crystallization", or as water molecules which are static components of protein structure.
Earth and agricultural sciences
In
soil science, hydrology and
agricultural sciences, water content has an important role for
groundwater recharge, agriculture, and
soil chemistry. Recent research has aimed toward a predictive-understanding of water content over space and time. In general, observations have revealed that spatial variance tends to increase as water content increases in semiarid regions, to decrease as water content increases in humid regions, and to peak at intermediate water contents in temperature regions .
There are four standard water contents that are routinely measured and used, which are described in the following table:
{]|-| Field capacity|align="center"| θpwp or θwp|align="right"| −1500|align="center"| 0.01–0.25| minimum soil moisture at which a plant wilts|-| Residual water content|align="center"|θr|align="right"| −∞|align="center"| 0.001–0.1| Remaining water at high tension|}
And lastly the [Available water capacity, θa, which is equivalent to:
θa ≡ θfc − θpwp
which can range between 0.1 in
gravel and 0.3 in
peat.
Agriculture
When a soil gets too dry, plant
transpiration drops because the water is becoming increasingly bound to the soil particles by suction. Below the
wilting point plants are no longer able to extract water. At this point they wilt and cease transpiring altogether. Conditions where soil is too dry to maintain reliable plant growth is referred to as agriculture drought, and is a particular focus of
irrigation management. Such conditions are common in
arid and semi-arid environments.
Some agriculture professionals are beginning to use environmental measurements such as soil moisture to schedule irrigation. This method is referred to as "Smart Irrigation."
Groundwater
In saturated groundwater aquifers, all available Porosity spaces are filled with water (volumetric water content =
porosity). Above a capillary fringe, pore spaces have air in them too.
Most soils have a water content less than porosity, which is the definition of unsaturated conditions, and they make up the subject of vadose zone hydrogeology. The capillary fringe of the
water table is the dividing line between
Aquifer#Saturated vs. unsaturated conditions. Water content in the capillary fringe decreases with increasing distance above the phreatic surface.
One of the main complications which arises in studying the vadose zone, is the fact that the unsaturated hydraulic conductivity is a function of the water content of the material. As 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.
A water retention curve is the relationship between water content and the water potential of the porous medium. It is characteristic for different types of porous medium. Due to hysteresis, different wetting and drying curves may be distinguished.
Normalized volumetric water content
The normalized water content, \Theta, (also called effective saturation or S_e) is a dimensionless value defined by van Genuchten as:
\Theta = \frac{\theta - \theta_r}{\theta_s-\theta_r}
where \theta is the volumetric water content; \theta_r is the residual water content, defined as the water content for which the gradient d\theta/dh becomes zero; and, \theta_s is the saturated water content.
See also
References
Water content or
moisture content is the quantity of water contained in a material, such as
soil (called
soil moisture),
Rock (geology), ceramics, or
wood on a volumetric or gravimetric basis. The property is used in a wide range of scientific and technical areas, and is expressed as a ratio, which can range from 0 (completely dry) to the value of the materials'
porosity at saturation.
Volumetric water content, θ, is defined mathematically as:
\theta = \frac{V_w}{V_b}
where V_w is the volume of water and V_b (or V_s for soil) is the bulk material volume. Water content may also be based on its mass or weight, thus the
gravimetric water content is defined as:
u = \frac{m_w}{m_b}
where m_w is the mass of water and m_b (or m_s for soil) is the bulk material mass.
To convert gravimetric water content to volumetric water, multiply the gravimetric water content by the bulk density of the material.
Measurement
Direct methods
Volumetric water content can be directly measured using a known volume of the material, and a drying oven. Volumetric water content, θ, is calculated using:
\theta = \frac{m_{wet}-m_{dry-->{\rho_w \cdot V_b}
where
m_{wet} and m_{dry} are the
masses of the sample before and after drying in the oven;
\rho_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
wood, the water content,
u, is expressed in terms of the mass of water per unit mass of the moist specimen:
u = \frac{m_{wet} - m_{dry-->{m_{wet-->
Laboratory methods
Other methods that determine water content of a sample include chemical titrations (for example the
Karl Fischer titration), determining mass loss on heating (perhaps in the presence of an inert gas), or after freeze drying. In the food industry the Dean-Stark apparatus is also commonly used.
From the Annual Book of ASTM (American Society for Testing and Materials) Standards, the total evaporable moisture content in Aggregate (C 566) can be calculated with the formula:
p = 100(W-D)/D
where:
p = total evaporable moisture content of sample, percent,W = mass of original sample, g, andD = mass of dried sample, g.
Geophysical methods
There are several
Geophysics methods available that can approximate
in situ soil water content. These methods include: time-domain reflectometry (TDR), neutron probe, frequency domain sensor,
capacitance probe,
electrical resistivity tomography, and others that are sensitive to the
Water (molecule). Geophysical sensors are often used to monitor soil moisture continuously in agricultural and scientific applications.
Satellite Remote Sensing Method
Satellite microwave remote sensing is used to estimate soil moisture based on the large contrast between the dielectric properties of wet and dry soil. The data from microwave remote sensing satellite such as: WindSat, AMSR-E, RADARSAT, ERS-1-2 are used to estimate surface soil moisture .
Classification and uses
Moisture may be present as adsorbed moisture at internal surfaces and as capillary condensed water in small pores. At low relative humidities, moisture consists mainly of adsorbed water. At higher relative humidities, liquid water becomes more and more important, depending on the pore size. In wood-based materials, however, almost all water is adsorbed at humidities below 98% RH.
In biological applications there can also be a distinction between physisorbed water and free water — the physisorbed water being that closely associated with and relatively difficult to remove from a biological material. The method used to determine water content may affect whether water present in this form is accounted for.
Water molecules may also be present in materials closely associated with individual molecules, as "water of crystallization", or as water molecules which are static components of protein structure.
Earth and agricultural sciences
In soil science, hydrology and agricultural sciences, water content has an important role for groundwater
recharge, agriculture, and soil chemistry. Recent research has aimed toward a predictive-understanding of water content over space and time. In general, observations have revealed that spatial variance tends to increase as water content increases in semiarid regions, to decrease as water content increases in humid regions, and to peak at intermediate water contents in temperature regions .
There are four standard water contents that are routinely measured and used, which are described in the following table:
{]|-| Field capacity|align="center"| θpwp or θwp|align="right"| −1500|align="center"| 0.01–0.25| minimum soil moisture at which a plant wilts|-| Residual water content|align="center"|θr|align="right"| −∞|align="center"| 0.001–0.1| Remaining water at high tension|}
And lastly the [Available water capacity, θa, which is equivalent to:
θa ≡ θfc − θpwp
which can range between 0.1 in
gravel and 0.3 in
peat.
Agriculture
When a soil gets too dry, plant transpiration drops because the water is becoming increasingly bound to the soil particles by suction. Below the
wilting point plants are no longer able to extract water. At this point they wilt and cease transpiring altogether. Conditions where soil is too dry to maintain reliable plant growth is referred to as
agriculture drought, and is a particular focus of irrigation management. Such conditions are common in arid and semi-arid environments.
Some agriculture professionals are beginning to use environmental measurements such as soil moisture to schedule irrigation. This method is referred to as "Smart Irrigation."
Groundwater
In saturated groundwater
aquifers, all available
Porosity spaces are filled with water (volumetric water content =
porosity). Above a
capillary fringe, pore spaces have air in them too.
Most soils have a water content less than porosity, which is the definition of unsaturated conditions, and they make up the subject of
vadose zone hydrogeology. The capillary fringe of the water table is the dividing line between Aquifer#Saturated vs. unsaturated conditions. Water content in the capillary fringe decreases with increasing distance above the phreatic surface.
One of the main complications which arises in studying the vadose zone, is the fact that the unsaturated hydraulic conductivity is a function of the water content of the material. As 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.
A water retention curve is the relationship between water content and the
water potential of the porous medium. It is characteristic for different types of porous medium. Due to hysteresis, different wetting and drying curves may be distinguished.
Normalized volumetric water content
The normalized water content, \Theta, (also called effective saturation or S_e) is a dimensionless value defined by van Genuchten as:
\Theta = \frac{\theta - \theta_r}{\theta_s-\theta_r}
where \theta is the volumetric water content; \theta_r is the residual water content, defined as the water content for which the gradient d\theta/dh becomes zero; and, \theta_s is the saturated water content.
See also
References
Anglian Water Services -
Anglian Water is one of the leading providers of water and wastewater services in the UK. ... privacy policy © Anglian Water Services Ltd 2005 Registered in England No. 2366656 ...
Anglian Water Services - alerts
Anglian Water is one of the leading providers of water and wastewater services in the UK. ... privacy policy © Anglian Water Services Ltd 2005 Registered in England No. 2366656 ...
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Water content - Wikipedia, the free encyclopedia
Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, or wood on a volumetric or gravimetric ...
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