Extracting freshwater from the air is the only way to meet all our freshwater needs

The Earth has a finite amount freshwater and nature has made sure that we do not run out of it. We can waste freshwater, contaminate it and misuse it but we cannot destroy even a drop of it. All we can do and have done is tap its supply to the extent that our demand exceeds nature's freshwater supply.  


The Water Cycle

The Hydrological Cycle
Source - Britannica.com

Known in scientific circles as the Hydrological Cycle, this cycle continuously delivers freshwater into the atmosphere, rivers, streams, lakes and underground aquifers. This renewing supply is a continuous one and mankind has developed ways to extract freshwater from every source except the atmosphere. 


Freshwater in the atmosphere
There are approximately 10.5 billion acre-feet of freshwater in the atmosphere.
2% of this freshwater exists as liquid droplets while 98% exists as water vapor. 
The freshwater in the air is more than 6 times the freshwater in all the rivers in the world.


Mankind is appropriating 54% of all Freshwater from traditional sources

Source - unwater.org

At the global level, 70% of the freshwater is used for agriculture, 22% by industry and 8% by people for drinking, cooking, sanitation etc.
At a population of 6 billion, mankind is appropriating 54% of all the freshwater in rivers, lakes and underground aquifers.
Our freshwater use has grown at a rate that is twice the rate of population growth. Thus, if these rates of increase continue, when the human population hits 9 billion in 2050, we will be appropriating more than 81% of all the freshwater in all the rivers, lakes and underground aquifers.


Difficult Choices
Thus, we have, simply speaking, just two options:
- Dramatically reduce the amount of freshwater we use, or
- Create or open up a new supply source for freshwater


This blog's efforts are focussed on tapping Nature's hydrological cycle at its freshwater source - the atmosphere.

Tears of Wine

Wine, a mixture of water and ethanol (a type of alcohol), exhibits a phenomenon that could be a part of the process to extract water vapor from air.


What is Air?
Air, is the name we have given to the atmosphere that is closest to the ground that contains a mixture (not chemical compound) of gases and water (in vapor, liquid and ice crystal form) that sustain and promote life, as we know it, on planet Earth.

Drops & Rivulets in a glass of wine
Source- www.monashscientific.com

Tears of Wine
Mixtures, that are physical and not chemical in nature, contain interfaces between the mixed materials. An example can be found by looking up in the air (an exaggerated one, I admit) - an interface exists between a cloud and the air around it. 
When an interface exists between materials that have very different surface tension forces, mass transfer occurs along their interface. 
The amount of mass transfer is impacted by a number of factors that include, amongst others,  the differing surface tension forces, temperature, pressure and evaporation rates.
This effect can be clearly seen in a glass of wine, in the formation of drops and rivulets on the insides of the glass surface above the wine surface.

Drops and rivulets in a wine glass
Source - newzstuff.blogspot.com

These drops and rivulets are the result of the different surface tensions of water and ethanol that constitute wine, and the fact that ethanol evaporates much faster than water does.
The scientific name for this phenomenon is: The Marangoni Effect.
In wine, as water and alcohol are not mixed completely homogeneously, different regions exist with different concentrations of water and of alcohol. 
In regions, where concentration of alcohol is greater, this alcohol pulls on the regions around it (where water concentration is greater) because the surface tension of alcohol is greater than the surface tension of water. The primary result is a movement of water away from alcohol and an increase in the separation between alcohol and water.

Moving a glass or
holding it at an angle
Source - 123rf.com

While this phenomenon was discovered and explained in the 1850s and 1860s, wine drinkers just know that they need to continuously move the wine glass in a circular pattern of motion to make the wine taste consistent and the one they had when the wine was pored from a freshly uncorked bottle.
This circular motion is really only focused on creating a more homogeneous mixture of alcohol and water. 
This motion does encourage increase in alcohol evaporation, and increased aeration (detrimental to taste and aroma?) but, hopefully, the wine is consumed before too much alcohol evaporates or too much air gets added to the mixture of water and alcohol.
Surface Tension Values Between Water and Air

Surface Tension
Interface	Temperature	milliNewtons per meter γ in (mN·m–1)
Water - air	20 °C	72.86±0.05[1]
Water - air	21.5 °C	72.75
Water - air	25 °C	71.99±0.05[1]

A Water Drop is Usually a Sphere but Never Shaped like a Tear-Drop

The shape of a "free" drop (or droplet) of water varies with the volume contained in the drop but is never shaped like a "tear-drop" that we are all familiar with and use to represent water.

Possible Source of the Tear-drop Shape

Common Representation of a water drop
Source - free.clipartof.com

The widely recognized representation of a water drop, in the shape of a tear-drop (shown on the right) simply does not exist except in our mind's eye. This shape probably originated from our observation of the appearance of water clinging to a surface or immediately before dropping from a surface (like a dripping tap). 

Water dripping from a Tap
Source - head-first.co.uk

Tiny drops of water
Source- Photography-on-the-net

The Primary Shape of a Water Drop is a Sphere

Water drops, smaller than 2 mm in size, take the shape of a perfect sphere. 

The drop takes this shape as a sphere is the geometric shape that has the smallest surface area for a given volume (see April 9, 2011 post). 

Also, the mass of water contained in a drop of this small size does not experience enough gravitational force for the shape to be impacted significantly. Simply speaking, the gravitational force is much less than the force of the Hydrogen Bonds in a drop of water.

The Shape of Raindrops depends on the size of the drop

Shapes of Raindrops of fifferent size
Source - http://en.wikipedia.org/wiki/Drop_(liquid)

As raindrops fall through the air they experience resistance from the air. This resistance is larger for larger drops and is insignificant, like the force of gravity, on drops less than 2mm in size.

As raindrop size grows,however, from the  combination of individual raindrops, the air resistance and gravity increase till they force the breakup of the large raindrops into smaller raindrops. These smaller raindrops again start exhibiting the spherical shape and combine into larger drops once again. This process of starting with tiny drops that combine to form larger drops which then break up into smaller drops, only stops when  raindrops reach the ground or some structure on the ground.

Why Does Water Form Drops?

Water forms drops whenever water molecules are attracted to each other by a force that is stronger than the attraction between water molecules and other molecules.

Water Beads into Drops in Air

2 water molecules conned by a "Hydrogen Bond"
Source-sweetwordsfromasourpatch.wordpress.com

Water molecules are made up of 2 hydrogen atoms and 1 atom of oxygen. These atoms are  arranged in a particular configuration that is unique to water molecules.

This arrangement of atoms produces a net charge (positive and negative) in different parts of the water molecule. This attribute of a water molecule is known as "polarity".

The existence of the negative and positive charges creates attraction (known as "hydrogen bonds") between water molecules.

In environments, like air, this bond is much stronger between water molecules than between a water molecule and any other negatively or positively charged molecule in air.

Water molecules forming 3-D structure of a drop
Source - ifm.liu.se

The result is the clustering of  a large number of water molecules together in a wide variety of configurations to form a 3-D structure, that we see and call a "water drop"

The shape is influenced by surface tension. More in my next post.

Surfaces Tailored to Extract Specific Dissolved Material

The human lung is an example of a 'surface' that has been designed to extract oxygen dissolved in air. A by-product of this process is the loss of water that occurs when we breathe.


The Human Lung
Resembling a sponge, the human lung contains over 70 square feet of surface area for 

A microscopic view inside the human lung
Source-www.environmentalgraffiti.com-image 8292

absorption of oxygen from the air we breathe. 

In an unstressed but not totally relaxed state, an adult typically takes 16 breaths a minute that process nearly 2000 gallons of air in a day.

During such 'normal' breathing, the inhaled air travels at a rate of about 50 mph to the lungs and over the inner surfaces in the lung.

Composition of Inhaled and Exhaled breath

Only a fraction of the oxygen inhaled is extracted by the lungs (Source-Users.ren.com)

Component	Inhaled Atmospheric Air (% volume)	Exhaled Air (% volume)
N2 (plus inert gases)	78.62	74.9
O2	20.85	15.3
CO2	0.03	3.6
H2O	0.5	6.2
	100.0%	100.0%

Exhaled air contains 120 times the moisture in the inhaled air. The typical human, thus, looses about half a liter of water through the act of breathing every day. This exhaled breath has a relative humidity of over a 100% and contains moisture picked up by the air from the moist surfaces of the lungs breathing passages.

Fish Gills

Source-http://www.oup.co.uk 

Just like human lungs are designed to extract oxygen from the air, fish gills are designed to extract oxygen dissolved in water.

When compared to water, air has over 20 times as much oxygen. Fish gills do their job in the oxygen-sparse water successfully, because the amount of oxygen required by a cold-blooded fish is very very small compared to that required by warm-blooded humans. 

It is for this reason, that whales who are warm-blooded need to surface periodically and 'breathe' the air.

And, it is for this same reason, that human lungs cannot breathe in water because human lungs do not have adequate surface area to extract necessary volumes of dissolved oxygen from water. Of course, evolution also is to blame as the linings of our lungs are probably not designed to function under water as they do in air.

Liquivent 

One way to help humans breathe under water would be to increase the amount of dissolved 

oxygen in water. Liquivent is just such a product in clinical testing - it is made up of per-fluorocarbons that can dissolve very large amounts of oxygen. It is expected that human lungs will be able to extract greater volumes of Oxygen without undue difficulty from per-fluorocarbons leading to smaller shoulder-tanks to breathe underwater.

Extracting water from air and wind may simply require the creation of a Liquivent-equivalent for water.