Physical basics Aquacontrol 102

As we can try out every morning at breakfast, a liquid, e.g. coffee, rises within a solid body, e.g. sugar cubes, without any external intervention.

Cause of this Phenomens are adhesion (i.e. interfacial adhesion of different substances) and cohesion forces (internal cohesion of molecules). These forces act in the capillaries, whose diameter is less than 0.1 mm and are therefore no longer visible to the naked eye, and cause the water to rise.

The capillary rise height is to be calculated as follows:

b(max) = 4o
(dxpxg)

d- inner diameter of the capillary in m
p- density of water 1000 kg/m3
g- gravity acceleration of the earth, 10 m/s2
o- Surface tension of water 0.075 N/m

With a capillary diameter of 0.01 mm, the climbing height is around 3m, i.e. up to the 1st floor!

The finer the capillaries, the The possible climbing height is higher. The building materials used in the walls also have an influence on this. However, this capillarity is not the only force that enables the transport of liquids in masonry. Other factors such as temperature and pressure differences, saturation, voltage, different pH values, radiation influences, etc. also have an influence. If the salt content in the masonry is very high, moisture will remain in the wall even if new barriers are installed. Pure water is normally non-conductive. However, as it travels through the capillaries of the soil and the wall, it absorbs various salts such as chlorides, phosphates or sulfates. As the salt solution flows past, charge separation occurs at the interfaces of the capillaries and thus a weak electric field with negative polarization is formed above. The salt ions, taking the water molecules with them, strive for this negative pole and so continue to rise upwards. The increase in tension causes a further increase in the climbing height. Anyone can check this themselves using suitable voltage measuring devices in the mV range. A flow potential of approx. 199.5 mV can be detected.

Normal compensation is only achieved in the so-called 0 potential line, just up to 3m above the ground. The entire area underneath is exposed to moisture.

The basic physical principle of enabling mass transport using differences in electrical charge is not new. Discovered over 100 years ago, it can now be found in many applications such as medicine or water technology. The corresponding physical processes have been sufficiently researched and proven in many experiments. The experimental setup is so simple that it can be carried out in virtually any school physics laboratory.

The direction and speed of the electroosmotic fluid flow follows the so-called Coehn's rule (from 1898):

V=(Er x Eo x U x Z)
(Eta xl)
V- speed of solution
Er-rel. Dielectric constant of the substance
Eo- abs. Dielectric constant of the liquid (= 8.86 x 49 251 93139589 A xsx V (-1) xm (-1)
U- applied voltage in volts

The higher the voltage applied, the greater the speed of solution transport. However, the limits are set by safety requirements and the standards and recommendations of electromagnetic compatibility (EMC) and the VDE. The water with the salts (H ) dissolved in it moves towards the cathode.

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