Environmental Engineering Reference
In-Depth Information
water. Langmuir observed a strong repulsive force between separate hydrophilic surfaces.
To dehydrate hydrophilic surfaces is to remove the strongly held layers of water of hydra-
tion, and this requires doing substantial work against these forces, called hydration forces.
These forces are very large but decrease rapidly over a range of a nanometer or less. They
are important in biology, particularly when cells are dehydrated by exposure to dry atmo-
spheres or to extracellular freezing.
We note how photosynthesis is used to produce starches and the complex molecule
chains starting from basic elements in the form of minerals and nutrients and convert
these into sugars and complex carbohydrates, from water and the energy provided by the
sun, drawing water up against gravity to bring these nutrients from the moist soil up and
through the roots and to the stems of plants and trees.
Owing to adhesion and surface tension, water exhibits capillary action whereby it rises
into a narrow tube against the force of gravity. Water adheres to the inside wall of the tube
and surface tension tends to straighten the surface, causing a surface rise and more water
being pulled up through cohesion. The process continues as the water lows up the tube
until there is enough water such that gravity balances the adhesive forces. Surface tension
and capillary action are important in biology. For example, when water is carried through
xylem of stems in plants, the strong intermolecular attractions (cohesion) hold the water
column together and adhesive properties maintain the water attachment to the xylem and
prevent tension rupture caused by transpiration pull. We note also how chemosynthesis
works by extracting sulfur from deep-water chimney stacks or little volcanoes, for plant
or animal life in the depths of our oceans that will never see the sun or any kind of light.
6.3 Cavitation
Viktor Schauberger, born in Austria in the 1880s, did pioneering work by systematically
studying, observing, and describing nature by thinking purely about how ish swam or
how birds lew with such effortless eficiency, and began applying these notions to solve
technical problems needed for the industrial applications during his own time. In the spe-
ciic case of cavitation, the original idea of Schauberger to work with vortices, especially in
water, comes from his own thorough studies of animals and nature. Reproducing many
of these resulted in various applications and inventions during his lifetime, including sev-
eral types of water treatment devices. We have come a long way since Schauberger in our
capacity to generate a vortex that has evolved by the availability of new precision equip-
ment and machining methods, and with the availability of new materials, instrumenta-
tion, and fabrication processes.
To gain some understanding of how cavitation works in water, we keep in mind that
water actually contains dissolved gases, and tap water for instance contains nitrogen and
oxygen similarly as found in air, but in proportions that are different from that of the
existing concentrations of the atmospheric air we breathe on land. By supplying mechani-
cal and/or electromagnetic forces to matter being accelerated, such as a body or a sound
wave moving through water, we can induce a set of controlled variations or pressure luc-
tuations events to enable cavitation to occur, or a temporary “delaminating” of a water
structure or surrounding medium. This is a common occurrence in ship or airplane pro-
pellers or impellers, and can be readily noticed when accelerating too quickly makes the
propeller lose “grip” with the water and air seems to get into the water, making engine
