Wetting and capillary movement in human life. Capillary phenomena (physics)

Surface tension is relatively easy to determine experimentally. There are various methods for determining surface tension, which are divided into static, semi-static and dynamic. Static methods are based on capillary phenomena associated with the curvature of the phase interface.

With the appearance of surface curvature between the phases, the internal pressure of the body changes and additional (capillary) Laplace pressure arises R, which can increase or decrease the internal pressure characteristic of a flat surface. This additional pressure can be represented as the resultant of surface tension forces directed to the center of curvature perpendicular to the surface. Curvature can be positive and negative (Fig. 2.2).

Rice. 2.2. Scheme of formation of additional pressure for a surface with positive (a) and negative (b) curvature

A change in the volume of liquid occurs as a result of a spontaneous decrease in surface energy and its conversion into mechanical energy changes in body volume. Moreover, in equation (2.2) for the Helmholtz energy at constant T,n,q only two terms should be considered dF = -pdV + ods. At equilibrium dF = 0, so pdV = ods. In this expression p = P- additional pressure (Lapplace pressure), equal to the pressure difference between the pressure of a body with flat and curved surfaces (AR):

The ratio is called surface curvature.

For a spherical surface. Substituting this expression

into the equation for additional pressure, we obtain the Laplace equation:

in which G- radius of curvature; - curvature or dispersion (Fig. 2.3).

If the surface has irregular shape, use the idea of mean curvature and Laplace’s equation has the form

where Gr /*2 are the main radii of curvature.

Rice. 2.3. Capillary rise of liquid during wetting (a) and non-wetting (O) capillary walls

For surface tension, Laplace's equation can be rewritten in the form showing the proportionality of the surface

tension to the capillary radius G and pressure R, in which a gas bubble escapes from a capillary immersed in a liquid. It is on this proportionality that Rebinder's method of experimental determination of surface tension is based.

The Rehbinder method measures the pressure at which a gas bubble escapes from a capillary immersed in liquid. At the moment the bubble passes through, the measured pressure will be equal to the capillary pressure, and the radius of curvature of the surface will be equal to the radius of the capillary. In experiment, it is almost impossible to measure the radius of a capillary, so relative measurements are made: the pressure in a gas bubble passing through a liquid with a known surface tension (this liquid is called standard) is determined, and then the pressure R in a gas bubble passing through a liquid with a detectable surface tension. Distilled water is usually used as a standard liquid, and double distillate is used for accurate measurements.

The ratio of the surface tension of a standard liquid to the pressure in the bubble that passes through it is called a constant

capillary With a known surface tension

(t 0 and measured pressures and R for the standard and test liquid, the surface tension of the latter is determined by the basic calculation formula of this method:

If the value is known with high accuracy, then the surface tension of the liquid being determined will also be accurate. Rebinder's method gives an accuracy in determining surface tension of up to 0.01 mJ/m 2.

When using the lifting method, the height of the rise (or fall) of the liquid in the capillary is measured and cc is compared with the height of rise of a standard liquid for which the surface tension is known (Fig. 2.4).

Rice. 2.4.

The reason for capillary rise is that the liquid, wetting the walls of the capillary, forms a certain curvature of the surface, and the resulting Laplace capillary pressure raises the liquid in the capillary until the weight of the liquid column balances the acting force. A rise in liquid in a capillary is observed when the curvature of the liquid surface is negative. With a concave meniscus, the Laplace pressure tends to stretch the liquid and lifts it; such capillary rise is called positive, it is characteristic of liquids that wet the walls of the capillary (for example, in the glass - water system). On the contrary, if the curvature of the surface is positive (convex meniscus), then additional pressure tends to compress the liquid and its lowering in the capillary is observed, which is called negative capillary rise. A similar phenomenon is typical for cases where the capillary walls are not wetted by liquid (for example, in a glass-mercury system).

Judging by Fig. 2.4. wetting affects the geometry of the surface and if r is the radius of curvature, then the radius of the capillary itself R connected with it by the relation

Where V- contact angle (acute when the capillary walls are wetted by the liquid). From the last relation it follows that

Substituting this relation into equation (2.4), we obtain

If we take into account that the pressure of the liquid column in the equation pdV = ods related to its height as mgh = V(p-p^)gh, you can get the ratio and then the Jurin formula:

Where h- height of liquid rise in the capillary; R- liquid density; ps- density of its saturated vapor; g- acceleration of gravity.

Provided that the density of the liquid R and its saturated vapor density ps incomparable (R » p s) for surface tension can be written

A more simplified formula also assumes complete wetting of the vessel walls with liquid (cos V = 1):

^ _ 2(7

gR(p-Ps)"

When using the method in practice, surface tension is calculated using the formula

where and h- height of rise in the capillary of the standard and test liquids; r^i r- their density.

This method can be used as an exact method under the condition cos in - const, better V= 0°, which is acceptable for many liquids without additional conditions. In the experiment, it is necessary to use thin capillaries that are well wetted by the liquid. The capillary rise method can also provide high accuracy in determining surface tension, up to 0.01-0.1 mJ/m

If you like to drink cocktails or other drinks from a straw, you have probably noticed that when one of its ends is dipped into liquid, the level of drink in it is slightly higher than in a cup or glass. Why is this happening? Usually people don't think about this. But physicists have long been able to study such phenomena well and even gave them their own name - capillary phenomena. Our turn has come to find out why this happens and how this phenomenon is explained.

Why do capillary phenomena occur?

In nature, everything that happens has a reasonable explanation. If the liquid is wetting (for example, water in a plastic tube), it will rise up the tube, and if it is non-wetting (for example, mercury in a glass flask), it will descend. Moreover, the smaller the radius of such a capillary, the greater the height the liquid will rise or fall. What explains such capillary phenomena? Physics says that they occur as a result of the influence of forces. If you look closely at the surface layer of liquid in a capillary, you will notice that its shape is a kind of circle. Along its border, the so-called surface tension exerts on the walls of the tube. Moreover, for a wetting liquid, its direction vector is directed downward, and for a non-wetting liquid, it is directed upward.

According to the third, it inevitably causes opposing pressure equal in magnitude to it. This is what causes the liquid in a narrow tube to rise or fall. This explains all kinds of capillary phenomena. However, many people probably already have a logical question: “When will the rise or fall of the liquid stop?” This will happen when the force of gravity, or the Archimedes force, balances the force causing the liquid to move through the tube.

How can capillary phenomena be used?

Almost every student is familiar with one of the applications of this phenomenon, which has become widespread in the production of stationery. You probably already guessed that we are talking about

Its design allows you to write in almost any position, and the thin and clear mark on the paper has long made this item very popular among the writing fraternity. also widely used in agriculture to regulate movement and conserve moisture in the soil. As you know, the soil where crops are grown has a loose structure, in which there are narrow spaces between its individual particles. In essence, these are nothing more than capillaries. Through them, water flows to the root system and provides the plants with the necessary moisture and beneficial salts. However, along these paths, soil water also rises and evaporates quite quickly. To prevent this process, capillaries should be destroyed. This is precisely why the soil is loosened. And sometimes the opposite situation arises when it is necessary to increase the movement of water through the capillaries. In this case, the soil is rolled, and due to this the number of narrow channels increases. In everyday life, capillary phenomena are used under a variety of circumstances. The use of blotting paper, towels and napkins, the use of wicks in and in technology - all this is possible due to the presence of narrow long channels in their composition.

Municipal educational institution "Lyceum No. 43"

(natural and technical)

CAPILLARY PHENOMENA
Rozhkov Dmitry

Saransk

2013
Table of contents

Literature review 3

Properties of liquids. Surface tension 3

Plateau Experience 6

Phenomena of wetting and non-wetting. Edge angle. 7

Capillary phenomena in nature and technology 8

Blood vessels 10

Foam in the service of man 11

Practical part 11

“Study of the capillary properties of various porous paper samples” 11

Conclusions and conclusions 13

Bibliography 13

Literature review

Capillary phenomena are physical phenomena caused by surface tension at the interface between immiscible media. Such phenomena usually include phenomena in liquid media caused by the curvature of their surface adjacent to another liquid, gas or its own vapor.

Capillary phenomena cover various cases of equilibrium and movement of the surface of a liquid under the influence of intermolecular interaction forces and external forces (primarily gravity). In the simplest case, when external forces are absent or compensated, the surface of the liquid is always curved. Thus, under conditions of weightlessness, a limited volume of liquid that is not in contact with other bodies takes the shape of a ball under the influence of surface tension. This shape corresponds to the stable equilibrium of the liquid, since the ball has a minimum surface area for a given volume and, therefore, the surface energy of the liquid in this case is minimal. The liquid also takes on the shape of a sphere if it is in another liquid of equal density (the effect of gravity is compensated by the Archimedean buoyancy force).

The properties of systems consisting of many small drops or bubbles (emulsions, liquid aerosols, foams) and the conditions for their formation are largely determined by the curvature of the surface of the particles, that is, capillary phenomena. Capillary phenomena play an equally important role in the formation of a new phase: liquid droplets during condensation of vapors, vapor bubbles during boiling of liquids, and nuclei of the solid phase during crystallization.

When a liquid comes into contact with solids, the shape of its surface is significantly influenced by wetting phenomena caused by the interaction of molecules of the liquid and the solid.

Capillary absorption plays a significant role in the water supply of plants and the movement of moisture in soils and other porous bodies. Capillary impregnation of various materials is widely used in chemical technology processes.

The curvature of the free surface of a liquid under the influence of external forces causes the existence of so-called capillary waves (“ripples” on the surface of the liquid). Capillary phenomena during the movement of liquid interfaces are considered by physicochemical hydrodynamics.

Capillary phenomena were first discovered and studied by Leonardo da Vinci, B. Pascal (17th century) and J. Jurin (Djurin, 18th century) in experiments with capillary tubes. The theory of capillary phenomena was developed in the works of P. Laplace (1806), T. Young (Young, 1805), J.W. Gibbs (1875) and I.S. Gromeki (1879, 1886).

Properties of liquids. Surface tension

The molecules of a substance in a liquid state are located almost close to each other. Unlike solid crystalline bodies, in which molecules form ordered structures throughout the entire volume of the crystal and can perform thermal vibrations around fixed centers, liquid molecules have greater freedom. Each molecule of a liquid, just like in a solid, is “sandwiched” on all sides by neighboring molecules and undergoes thermal vibrations around a certain equilibrium position. However, from time to time, any molecule may move to a nearby vacant location. Such jumps in liquids occur quite often; therefore, the molecules are not tied to specific centers, as in crystals, and can move throughout the entire volume of the liquid. This explains the fluidity of liquids. Due to the strong interaction between closely located molecules, they can form local (unstable) ordered groups containing several molecules. This phenomenon is called short-range order (Fig. 1).

Due to the dense packing of molecules, the compressibility of liquids, i.e., the change in volume with a change in pressure, is very small; it is tens and hundreds of thousands of times less than in gases.

Liquids, like solids, change their volume with changes in temperature. For not very large temperature intervals, the relative change in volume ΔV/V 0 is proportional to the change in temperature ΔT:

The coefficient β is called the temperature coefficient of volumetric expansion. The thermal expansion of water has an interesting and important anomaly for life on Earth. At temperatures below 4°C, water expands. Water has a maximum density ρ in = 10 3 kg/m 3 at a temperature of 4°C.

When water freezes, it expands, so ice remains floating on the surface of a freezing body of water. The temperature of freezing water under the ice is 0°C. In denser layers of water, at the bottom of the reservoir, the temperature is about 4 °C. Thanks to this, life can exist in the water of freezing reservoirs.

The most interesting feature of liquids is the presence of a free surface. Liquid, unlike gases, does not fill the entire volume of the container into which it is poured. An interface is formed between liquid and gas (or vapor), which is in special conditions compared to the rest of the liquid. Molecules in the boundary layer of a liquid, unlike molecules in its depth, are not surrounded by other molecules of the same liquid on all sides. The forces of intermolecular interaction acting on one of the molecules inside a liquid from neighboring molecules are, on average, mutually compensated. Any molecule in the boundary layer is attracted by molecules located inside the liquid (the forces acting on a given liquid molecule from gas (or vapor) molecules can be neglected). As a result, a certain resultant force appears, directed deep into the liquid (Fig. 2)

Fig.2

If a molecule moves from the surface into the liquid, the forces of intermolecular interaction will do positive work. On the contrary, in order to pull a certain number of molecules from the depth of the liquid to the surface (i.e., to increase the surface area of the liquid), it is necessary to expend positive work of external forces ΔA external, proportional to the change ΔS of the surface area:
ΔA external = σΔS.
The coefficient σ is called the surface tension coefficient (σ > 0). Thus, the coefficient of surface tension is equal to the work required to increase the surface area of a liquid at constant temperature by one unit.

In SI, the coefficient of surface tension is measured in joules per square meter (J/m2) or in newtons per meter (1 N/m = 1 J/m2).

Consequently, the molecules of the surface layer of a liquid have excess potential energy compared to the molecules inside the liquid. The potential energy E p of the liquid surface is proportional to its area:
E p = A external = σS.
It is known from mechanics that the equilibrium states of a system correspond to the minimum value of its potential energy. It follows that the free surface of the liquid tends to reduce its area. For this reason, a free drop of liquid takes on a spherical shape (Fig. 3)
.

Fig.3
The liquid behaves as if forces acting tangentially to its surface are contracting (pulling) this surface. These forces are called surface tension forces.

The presence of surface tension forces makes the surface of a liquid look like an elastic stretched film, with the only difference that the elastic forces in the film depend on its surface area (i.e., on how the film is deformed), and the surface tension forces do not depend on the surface area liquids.

Since any system spontaneously passes into a state in which its potential energy is minimal, the liquid must spontaneously transform into a state in which its free surface area has the smallest value. This can be shown using the following experiment.

A movable cross member is attached to a wire bent in the shape of the letter P (Fig. 4). The frame thus obtained is covered with soap film, lowering the frame into a soap solution. After removing the frame from the solution, the crossbar moves upward, i.e., molecular forces actually reduce the free surface area of the liquid.

Fig.4
Since, for the same volume, a sphere has the smallest surface area, the liquid in a state of weightlessness takes the shape of a sphere. For the same reason, small drops of liquid have a spherical shape. The shape of soap films on various frames always corresponds to the smallest free surface area of the liquid.

Plateau Experience

The natural shape of any liquid is a sphere. Typically, gravity prevents the liquid from taking this shape, and the liquid either spreads out in a thin layer, if there is no container, or takes the shape of the container. When inside another liquid of the same density, the liquid takes on a natural, spherical shape.

Fig.5
Olive oil floats in water but sinks in alcohol. You can prepare a mixture of water and alcohol in which the oil will be in equilibrium. Using a glass tube or syringe, introduce a little olive oil into this mixture: the oil will collect into one spherical drop, which will hang motionless in the liquid. If you pass a wire through the center of the oil ball and rotate it, the oil ball begins to flatten, and then, after a few seconds, a ring of small spherical droplets of oil separates from it. This experiment was first carried out by the Belgian physicist Plateau.

On a gigantic scale, this phenomenon can be observed in our star, the Sun, and the giant planets. These celestial bodies rotate around their axis very quickly. As a result of this rotation, the bodies are very strongly compressed at the poles.

Fig.6

Phenomena of wetting and non-wetting. Edge angle.

Wetting and non-wetting - capillary phenomena are widespread in nature and technology. They are important both in Everyday life, and for solving the most important scientific and technical problems. Knowledge on these issues allows you to answer many questions. For example, that capillary phenomena allow the absorption of nutrients and moisture from the soil by the root system of vegetation, that blood circulation in living organisms is based on the capillary phenomenon, what is flotation and where is it used, why some solids are well wetted by liquid, others poorly, etc. .

If you dip a glass rod into mercury and then remove it, there will be no mercury on it. If you put this stick in water, then after pulling it out, a drop of water will remain at its end. This experiment shows that mercury molecules are attracted to each other more strongly than to glass molecules, and water molecules are attracted to each other less than to glass molecules.

If the molecules of a liquid are attracted to each other less than to the molecules of a solid, then the liquid is called wetting this substance. For example, water wets clean glass but does not wet paraffin. If the molecules of a liquid are attracted to each other more strongly than to the molecules of a solid substance, then the liquid is called non-wetting of this substance. Mercury does not wet glass, but it does wet pure copper and zinc.

Let us place a horizontally flat plate of some solid substance and drop the liquid under study onto it. Then the drop will be located either as shown in Fig. 7( A), or as shown in Fig. 7( b).

a) b)

Fig.7.
In the first case, the liquid wets solid, but in the second - no. The angle θ marked in Fig. 5 is called contact angle. The contact angle is formed by the flat surface of a solid and a plane tangent to the free surface of the liquid, where they border solid, liquid and gas; There is always liquid inside the contact angle. For wetting liquids the contact angle is acute, and for non-wetting liquids it is obtuse. To prevent the action of gravity from distorting the contact angle, the drop should be taken as small as possible.

Since the contact angle θ is maintained when the solid surface is in a vertical position, the wetting liquid at the edges of the vessel into which it is poured rises, and the non-wetting liquid sinks

With complete wetting, θ = 0, cos θ = 1.

Fig.8

Capillary phenomena in nature and technology

The rise of the liquid in the capillary continues until the force of gravity acting on the column of liquid in the capillary becomes equal in magnitude to the resulting F n surface tension forces acting along the boundary of contact of the liquid with the surface of the capillary: F t = F n, where F t = mg = ρhπr 2 g, F n = σ2πr cos θ.

This implies:

The curvature of the liquid surface in narrow tubes leads to an apparent violation of the law of communicating vessels.

From the formula it is clear that the height h the larger the smaller the inner radius of the tube r. The rise of water is significant in tubes whose internal diameter is comparable to the diameter of a hair (or even less); Therefore, such tubes are called capillaries (from the Greek “capillaris” - hairy, thin). The wetting liquid in the capillaries rises up (Fig. 9, a), and the non-wetting liquid goes down (Fig. 9, a) b).

Fig.9

Capillary phenomena can be observed not only in tubes, but also in narrow crevices. If you lower two glass plates into water so that a narrow gap forms between them, then the water between the plates will rise, and the higher the closer they are located, the higher. Capillary phenomena play an important role in nature and technology. There are many tiny capillaries in plants. In trees, through capillaries, moisture from the soil rises to the tops of the trees, where it evaporates through the leaves into the atmosphere. The soil has capillaries, which are narrower the denser the soil. Water rises through these capillaries to the surface and quickly evaporates, and the ground becomes dry. Early spring plowing of the land destroys capillaries, i.e. it preserves subsoil moisture and increases the yield.

In technology, capillary phenomena are of great importance, for example, in the processes of drying capillary-porous bodies, etc. Great importance capillary phenomena occur in the construction industry. For example, to prevent a brick wall from becoming damp, a gasket is made between the foundation of the house and the wall from a substance that does not contain capillaries. In the paper industry, capillarity has to be taken into account when producing different grades of paper. For example, when making writing paper, it is impregnated with a special compound that clogs the capillaries. In everyday life, capillary phenomena are used in wicks, in blotting paper, in pens for supplying ink, etc.

Most plant and animal tissues are penetrated by a huge number of capillary vessels. It is in the capillaries that the main processes associated with respiration and nutrition of the body take place; all the complex chemistry of life is closely related to diffusion phenomena. Tree trunks, branches and plant stems are penetrated by a huge number of capillary tubes, through which nutrients rise to the very top leaves. The root system of plants ends in the finest capillary threads. And the soil itself, the source of nutrition for the root, can be represented as a set of capillary tubes through which, depending on the structure and processing, water with substances dissolved in it rises faster or slower to the surface. The smaller the diameter, the greater the height of liquid rise in capillaries. From here it is clear that to preserve moisture, the soil must be dug up, and to drain, it must be compacted.

The role of surface phenomena in nature is varied. For example, the surface film of water provides support for many organisms when moving. This form of movement is found in small insects and arachnids. The most famous are water striders, which rest on the water only with the end segments of their widely spaced legs. The foot, covered with a waxy coating, is not wetted by water; the surface layer of water bends under the pressure of the foot, forming a small depression. Shore spiders of some species move in a similar way, but their legs are not located parallel to the surface of the water, like those of water striders, but at right angles to it.

Some animals that live in water, but do not have gills, are suspended from below to the surface film of water with the help of non-wettable bristles surrounding their respiratory organs. This technique is “used” by mosquito larvae (including malaria ones).

The feathers and down of waterfowl are always richly lubricated with fatty secretions of special glands, which explains their waterproofness. A thick layer of air, enclosed between the duck's feathers and not displaced by water, not only protects the duck from heat loss, but also greatly increases its reserve of buoyancy, acting like a lifebelt.

A waxy coating on the leaves prevents the so-called stomata from flooding, which could lead to disruption of proper plant respiration. The presence of the same waxy coating explains the waterproofness of a thatched roof, haystacks, etc.

The main moisture-consuming organ, where water is constantly needed, including for photosynthesis, is the leaf, located far from the root. In addition, the leaf is surrounded by air, which often “takes away” water from it in order to “be saturated” with water vapor. A contradiction arises: the leaf constantly needs water, but it constantly loses it, and the root constantly has water in excess, although it is not averse to getting rid of it. The solution to this problem is obvious: you need to pump excess water from the root to the leaves. The role of such a water supply system is taken over by the stem. It delivers water to the leaves through special tubes - capillaries. In angiosperms, they are the most perfect and are long (as tall as the plant itself) hollow vessels, the walls of which are lined with cellulose and lignin. The system of such conducting vessels is called xylem (from the Greek xylon - tree, wooden block).

If mineral substances that the root has absorbed from the soil are concentrated in the lumen of the root xylem vessels, water rushes into the xylem from the surrounding root cells through the mechanism of osmosis.

The “water pumping” mechanism consists of two osmotic pumps and the capillary forces of the vessel walls.

Blood vessels

The entire body is penetrated by blood vessels. They are not the same in structure. Arteries are vessels through which blood moves away from the heart. They have dense elastic elastic walls, which contain smooth muscles. As the heart contracts, it pumps blood into the artery under high pressure. Due to their density and elasticity, the artery walls withstand this pressure and stretch.

Large arteries branch as they move away from the heart. The smallest arteries break up into the thinnest capillaries. Their walls are formed by a single layer of flat cells. Through the walls of the capillaries, substances dissolved in the blood plasma pass into the tissue fluid, and from it enter the cells. Cell waste products penetrate through the walls of capillaries from tissue fluid into the blood. There are approximately 150 billion capillaries in the human body. If all the capillaries are drawn into one line, then it can encircle the globe along the equator two and a half times. Blood from capillaries collects into veins - vessels through which blood moves to the heart. The pressure in the veins is low, their walls are thinner than the walls of the arteries.

Foam in the service of man

It was not theory that led to the very idea of flotation, but careful observation of a random fact. At the end of the 19th century. American teacher Currie Everson, while washing oily bags in which copper pyrite was stored, noticed that grains of pyrite floated up with soap foam. This was the impetus for the development of the flotation method. This method is widely used in the mining and metallurgical industry for ore beneficiation, i.e. to increase the relative content of valuable components in them. The essence of flotation is as follows. Finely ground ore is loaded into a vat with water and oily substances, which are capable of enveloping the particles of the useful mineral with a thin film that is not wetted by water. The mixture is vigorously mixed with air, so that many tiny bubbles are formed - foam. In this case, particles of the useful mineral, coated in a thin oily film, when in contact with the shell of the air bubble, stick to it, hang on the bubble and are carried up with it, like on a balloon. Particles of waste rock, not enveloped in an oily substance, do not stick to the shell and remain in the liquid. As a result, almost all of the useful mineral particles end up in foam on the surface of the liquid. The foam is removed and sent for further processing - to obtain the so-called concentrate .

The flotation technique allows, with the proper selection of mixed liquids, to separate the required useful mineral from gangue rock of any composition.

Practical part

“Study of the capillary properties of various porous paper samples”

Goal of the work: study the capillary properties of various samples of porous paper (using the example of paper napkins from different manufacturers).

Devices and materials: paper samples, distilled water, ruler, bath.

Execution method:

Manufacturer's name			Design capillary radius, 10 -5 m
	2,25 2,3	2,25	0,6621	4
BRIZ LLC, Novorossiysk	1,8 1,75	1,78	0,837	3
	1,3 1,25	1,32	1,1286	2
	2,5 2,1	2,26	0,6592	4

I repeated the experiment, replacing the water with milk.

Milk 2.5%;

In the calculations I used the following table values:

 – density of milk (1.03x10 3 kg/m 3);

 – surface tension (for milk at the border with air  = 46x10 -3 N/m)

Manufacturer's name	Liquid lifting height, 10 -2 m	Average height of liquid rise, 10 -2 m	Design capillary radius, 10 -3 m	Assessment of the quality of moisture absorption using a 4-point system
LLC "Russian Paper ALL Products" Bryansk	1,1 1,1	1,09	0,836	4
BRIZ LLC, Novorossiysk	0,8 0,55	0,64	1,424	3
New Technologies LLC, Krasnodar	0,3 0,38	0,31	2,94	2
IP Kitaikin A.B. Novoshakhtinsk, Rostov region.	0,98 1,0	0,97	0,94	4

Conclusions and Conclusions

As a result of the work carried out, an objective assessment of the quality of paper napkins from various manufacturers was obtained.
The best results were shown by samples from the following manufacturers: Russian Paper ALL Products LLC, Bryansk and IP Kitaykin A.B. Novoshakhtinsk, Rostov region.
The worst were napkins from New Technologies LLC, Krasnodar, manufactured for the Magnit chain of stores.
The best napkins can be recommended for use in the canteen of Lyceum No. 43.

Bibliography

Physical encyclopedia. http://enc-dic.com/enc_physics/Kapilljarne-javlenija-911.html
Properties of liquids http://physics.kgsu.ru/index.php?option=com_content&view=article&id=161&Itemid=72#q3
Capillary phenomena. http://seaniv2006.narod.ru/1191.html (03.12.12)

) — force due to capillary phenomena. Capillary phenomena include surface phenomena at the interface of a liquid with another medium, associated with its curvature.

Description

The curvature of the liquid surface at the boundary with the gas phase occurs as a result of the action of surface tension of the liquid, which tends to shorten the interface and give the limited volume of liquid a shape with the lowest potential of surface tension forces. Surface tension forces create additional pressure (capillary pressure) below the phase interface, the magnitude of which is determined by Laplace’s formula:

where is surface tension, and - average radius of curvature of the surface.

In the case of sufficiently large masses of liquid, the effect of surface tension is compensated by gravity, therefore capillary phenomena manifest themselves primarily when the liquid is in narrow channels (capillaries) and porous media.

In a narrow channel, the interface between liquid and gas takes on a curved shape (meniscus), convex in the case of non-wetting of the capillary walls by the liquid and concave in the case of wetting. A convex meniscus creates excess pressure under its surface, while a concave meniscus creates negative pressure (rarefaction). The latter phenomenon causes liquid to flow into capillaries with wetted walls, including against gravity, which plays an important role in many biological processes. Capillary phenomena in porous media are responsible for the spread of groundwater, impregnation of tissues and other fibrous materials with liquids (wick effect). When two rough wetted surfaces interact near local contact spots, liquid menisci appear, leading to the appearance of capillary.

Illustrations

Authors

Goryacheva Irina Georgievna
Shpenev Alexey Gennadievich

Sources

Capillary action // Wikipedia, the free Encyclopedia. -www.en.wikipedia.org/wiki/Capillary_action (access date: 07/26/2010).
Capillary phenomena // Chemical encyclopedia. T. 2. - M.: Soviet Encyclopedia, 1990. P. 310–311.
Capillary phenomena // Great Soviet Encyclopedia. 3rd ed., 1969–1978.

Change the level in tubes, narrow channels of arbitrary shape, porous bodies. A rise in liquid occurs in cases where channels are wetted by liquids, for example, water in glass tubes, sand, soil, etc. A decrease in liquid occurs in tubes and channels that are not wetted by liquid, for example, mercury in a glass tube.

The vital activity of animals and plants, chemical technologies, and everyday phenomena (for example, lifting kerosene along the wick in a kerosene lamp, wiping hands with a towel) are based on capillarity. Soil capillarity is determined by the rate at which water rises in the soil and depends on the size of the spaces between soil particles.

Capillaries are thin tubes, as well as the thinnest vessels in the human body and other animals (see Capillary (biology)).

Literature

Prokhorenko P. P. Ultrasonic capillary effect / P. P. Prokhorenko, N. V. Dezhkunov, G. E. Konovalov; Ed. V. V. Klubovich. 135 p. Minsk: “Science and Technology”, 1981.

Links

Gorin Yu. V. Index of physical effects and phenomena for use in solving inventive problems (TRIZ tool) // Chapter. 1.2 Surface tension of liquids. Capillarity.

Wikimedia Foundation. 2010.

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The word capillary is used to describe very narrow tubes through which liquid can pass. For more details, see the article Capillary effect. Capillary (biology) is the smallest type of blood vessel. Capillary (physics) Capillary... ... Wikipedia

Landau criterion for superfluidity is the relationship between the energies and momenta of elementary excitations of a system (phonons), which determines the possibility of its being in a superfluid state. Contents 1 Formulation of the criterion 2 Conclusion of the criterion ... Wikipedia

External unit of split systems and condensers (fan cooling towers) of commercial refrigeration equipment on one rack Climate and refrigeration equipment equipment based on the operation of refrigeration machines ... Wikipedia

A change in gas temperature as a result of its slow flow under the influence of a constant pressure drop through a throttle; a local obstacle to the gas flow (capillary, valve or porous partition located in the pipe along the way... ...

It is a colorless transparent liquid, boiling at atmospheric pressure at a temperature of 4.2 K (liquid 4He). The density of liquid helium at a temperature of 4.2 K is 0.13 g/cm³. It has a low refractive index, due to... ... Wikipedia

The fountaining effect, the appearance in a superfluid liquid of a pressure difference Δр caused by a temperature difference ΔТ (see Superfluidity). T. e. manifests itself in liquid superfluid helium in the difference in liquid levels in two vessels,... ... Great Soviet Encyclopedia

Each of us can easily recall many substances that he considers liquids. However, it is not so easy to give an exact definition of this state of matter, since liquids have such physical properties that in some respects they... ... Collier's Encyclopedia

Capillarity (from Latin capillaris hair), capillary effect physical phenomenon, which consists in the ability of liquids to change the level in tubes, narrow channels of arbitrary shape, and porous bodies. A rise in fluid occurs in cases of... ... Wikipedia